Health effects of electronic cigarettes

When evaluating the health effects of some activity, a reasonable question is "what is the practical alternative?" If the alternatives are worse, then the activity must be measured against the alternatives. If the alternative is smoking, the answer might be different than if the alternative is simply to avoid nicotine. This is because the health impacts of smoking are strongly negative, while the impacts of avoiding nicotine entirely are positive.

E-cigarette vapor does not contain tobacco and does not involve combustion, therefore users do not encounter several harmful constituents of tobacco smoke, such as ash, tar, and carbon monoxide.{{cite journal |vauthors=Smith L, Brar K, Srinivasan K, Enja M, Lippmann S |date=June 2016 |title=E-cigarettes: How "safe" are they? |url=http://www.mdedge.com/jfponline/article/109243/addiction-medicine/e-cigarettes-how-safe-are-they |journal=The Journal of Family Practice |volume=65 |issue=6 |pages=380–385 |pmid=27474819}} A 2014 review concluded that e-cigarette aerosol contains far fewer carcinogens than tobacco smoke, and concluded that e-cigarettes "impart a lower potential disease burden" than traditional cigarettes.{{cite journal |vauthors=Oh AY, Kacker A |date=December 2014 |title=Do electronic cigarettes impart a lower potential disease burden than conventional tobacco cigarettes? Review on E-cigarette vapor versus tobacco smoke |journal=The Laryngoscope |volume=124 |issue=12 |pages=2702–2706 |doi=10.1002/lary.24750 |pmid=25302452 |s2cid=10560264 |doi-access=free}} However, e-cigarette vapor has components not present in traditional cigarettes, which potentially offset some of these benefits.

Smokers can use e-cigarettes for various purposes. As an aid to quitting smoking, vaping is a temporary activity that reduces smoking and terminates once the smoker has completed the transition away from nicotine. To the extent that vaping aids the transition, its health effects are positive.

Alternatively, smokers can substitute vaping for smoking without intending to transition. In this context, vaping is still preferred.{{cite journal |vauthors=Palazzolo DL |date=November 2013 |title=Electronic cigarettes and vaping: a new challenge in clinical medicine and public health. A literature review |journal=Frontiers in Public Health |volume=1 |issue=56 |page=56 |doi=10.3389/fpubh.2013.00056 |pmc=3859972 |pmid=24350225 |doi-access=free|bibcode=2013FrPH....1...56P }}{{CC-notice|cc=by3|url=http://journal.frontiersin.org/article/10.3389/fpubh.2013.00056/full|author(s)=Dominic L. Palazzolo}} However, if vaping is used as a way to get nicotine in situations where smoking is not convenient, vaping may negatively affect health.

Other smoker-transition aids are available and may offer better safety and/or effectiveness{{Cn|date=June 2025}} profiles then vaping. Given equal effectiveness, relatively safety considerations would become paramount.{{cite journal |vauthors=Kalkhoran S, Glantz SA |date=February 2016 |title=E-cigarettes and smoking cessation in real-world and clinical settings: a systematic review and meta-analysis |journal=The Lancet. Respiratory Medicine |volume=4 |issue=2 |pages=116–128 |doi=10.1016/S2213-2600(15)00521-4 |pmc=4752870 |pmid=26776875}} However, a large-scale 2025 analysis indicated that other smoking cessation products are less effective at aiding transition than vaping.

File:JUUL_e-cigarette_with_a_battery_and_differently_flavored_pods.jpg

Vaping presents health risks that are definitionally higher than those of simple abstinence, as no independent health benefits have been reported, while nicotine and cannabis have well-established harms. This comparison is relevant because some never-smokers adopt e-cigarettes for these drugs. Once dependence is established, users may be more likely to take up smoking.

Health effects for non-smokers must be considered in absolute terms for long-term use as well as the risk of transition into traditional cigarettes, while for smokers the relative risks are paramount, and if used as a quitting aid, any short-term effects are most important.

E-cigarettes create nicotine dependence in non-smokers.{{Cite web |last=CDC |date=2024-05-28 |title=Health Effects of Vaping |url=https://www.cdc.gov/tobacco/e-cigarettes/health-effects.html |access-date=2025-01-03 |website=Smoking and Tobacco Use |language=en-us}} E-cigarettes may act as a gateway drug to smoking, particularly among youth.{{Cite journal |last1=Banks |first1=Emily |last2=Yazidjoglou |first2=Amelia |last3=Brown |first3=Sinan |last4=Nguyen |first4=Mai |last5=Martin |first5=Melonie |last6=Beckwith |first6=Katie |last7=Daluwatta |first7=Amanda |last8=Campbell |first8=Sai |last9=Joshy |first9=Grace |date=2022 |title=Electronic cigarettes and health outcomes: systematic review of global evidence |url=https://openresearch-repository.anu.edu.au/items/f48084ef-c1e5-439f-8af2-9d78506ae577 |journal=ANU Research Publications- Open Research Repository |language=en-AU |doi=10.25911/XV0F-6C42}}{{cite web |date=20 January 2016 |title=Headlines about e-cigarettes don't mean they're 'not safer than tobacco' |url=http://scienceblog.cancerresearchuk.org/2016/01/20/headlines-about-e-cigarettes-dont-mean-theyre-not-safer-than-tobacco/ |archive-url=https://web.archive.org/web/20190214174323/https://scienceblog.cancerresearchuk.org/2016/01/20/headlines-about-e-cigarettes-dont-mean-theyre-not-safer-than-tobacco/ |archive-date=14 February 2019 |access-date=13 February 2019 |publisher=Cancer Research UK |vauthors=Smith N}} Pregnant or nursing women and the elderly are more sensitive to nicotine than other individuals.{{cite journal |vauthors=Schraufnagel DE |date=March 2015 |title=Electronic Cigarettes: Vulnerability of Youth |journal=Pediatric Allergy, Immunology, and Pulmonology |volume=28 |issue=1 |pages=2–6 |doi=10.1089/ped.2015.0490 |pmc=4359356 |pmid=25830075}}

Used to transition to abstinence, e-cigarettes end the consumption of nicotine and the other harmful substances in tobacco smoke and later any harmful e-liquid ingredient. However, if abstinence is not achieved, e-cigarettes could mean increased nicotine dependence (by adding vaping to smoking) and ongoing harm from other e-liquid ingredients.{{cite journal |vauthors=Nansseu JR, Bigna JJ |year=2016 |title=Electronic Cigarettes for Curbing the Tobacco-Induced Burden of Noncommunicable Diseases: Evidence Revisited with Emphasis on Challenges in Sub-Saharan Africa |journal=Pulmonary Medicine |volume=2016 |page=4894352 |doi=10.1155/2016/4894352 |pmc=5220510 |pmid=28116156 |doi-access=free}}{{CC-notice|cc=by4|url=https://www.hindawi.com/journals/pm/2016/4894352/|author(s)=Jobert Richie N. Nansseu and Jean Joel R. Bigna}}{{cite journal |vauthors=Jankowski M, Krzystanek M, Zejda JE, Majek P, Lubanski J, Lawson JA, Brozek G |date=June 2019 |title=E-Cigarettes are More Addictive than Traditional Cigarettes-A Study in Highly Educated Young People |journal=International Journal of Environmental Research and Public Health |volume=16 |issue=13 |page=2279 |doi=10.3390/ijerph16132279 |pmc=6651627 |pmid=31252671 |doi-access=free}}{{cite web |year=2013 |title=Electronic Cigarettes – An Overview |url=http://www.dkfz.de/en/presse/download/RS-Vol19-E-Cigarettes-EN.pdf |publisher=German Cancer Research Center}}

Health benefits associated with transitioning from smoking to vaping include decreased post-smoking weight gain and improved exercise tolerance.{{cite journal |vauthors=Sanford Z, Goebel L |year=2014 |title=E-cigarettes: an up to date review and discussion of the controversy |journal=The West Virginia Medical Journal |volume=110 |issue=4 |pages=10–15 |pmid=25322582}}

Even a partially successful transition may allow smokers to reduce their cigarette consumption with related health benefits.{{cite journal |vauthors=Smith L, Brar K, Srinivasan K, Enja M, Lippmann S |date=June 2016 |title=E-cigarettes: How "safe" are they? |journal=The Journal of Family Practice |volume=65 |issue=6 |pages=380–385 |pmid=27474819}} A 2022 Cochrane review concluded that vaping increased quit rates compared to e-cigarettes without nicotine and compared to nicotine replacement therapy, although it did not compare vaping to other methods.{{cite journal |vauthors=Hartmann-Boyce J, Lindson N, Butler AR, McRobbie H, Bullen C, Begh R, Theodoulou A, Notley C, Rigotti NA, Turner T, Fanshawe TR, Hajek P |date=November 2022 |title=Electronic cigarettes for smoking cessation |journal=The Cochrane Database of Systematic Reviews |volume=11 |issue=11 |pages=CD010216 |doi=10.1002/14651858.CD010216.pub7 |pmc=9668543 |pmid=36384212}}{{Update inline|reason=Updated version https://www.ncbi.nlm.nih.gov/pubmed/38189560|date=October 2024}}

The relative safety of electronic versus conventional cigarettes is disputed. 2015{{cite web |date=August 2015 |title=E-cigarettes: an evidence update |url=https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/454516/Ecigarettes_an_evidence_update_A_report_commissioned_by_Public_Health_England.pdf |publisher=Public Health England |pages=1–113 |vauthors=McNeill A, Brose LS, Calder R, Hitchman SC, Hajek P, McRobbie H |location=UK}}{{rp|76}} and 2018 Public Health England (PHE) reports claimed that vaping is "at least 95% less harmful than smoking".{{cite web |date=February 2018 |title=Evidence review of e-cigarettes and heated tobacco products 2018 |url=https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/684963/Evidence_review_of_e-cigarettes_and_heated_tobacco_products_2018.pdf |publisher=Public Health England |pages=1–243 |vauthors=McNeill A, Brose LS, Calder R, Bauld L, Robson D |location=UK}}{{rp|175}} The Royal College of Physicians, the Royal Society for Public Health, and the National Health Service backed these claims.{{cite journal |vauthors=Glantz SA, Bareham DW |date=April 2018 |title=E-Cigarettes: Use, Effects on Smoking, Risks, and Policy Implications |journal=Annual Review of Public Health |volume=39 |issue=1 |pages=215–235 |doi=10.1146/annurev-publhealth-040617-013757 |pmc=6251310 |pmid=29323609}}{{CC-notice|cc=by4|url=http://www.annualreviews.org/doi/pdf/10.1146/annurev-publhealth-040617-013757|author(s)=Stanton A. Glantz and David W. Bareham}} The estimate was limited by "lack of hard evidence for the harms of most products on most of the criteria". The research was funded by EuroSwiss Health and was criticized for its weak methodology,{{cite journal |vauthors=Couch ET, Chaffee BW, Gansky SA, Walsh MM |date=July 2016 |title=The changing tobacco landscape: What dental professionals need to know |journal=Journal of the American Dental Association |volume=147 |issue=7 |pages=561–569 |doi=10.1016/j.adaj.2016.01.008 |pmc=4925234 |pmid=26988178}} lack of specific evidence, and for financial ties to the tobacco industry. The estimate was disputed in medical journals.{{cite journal |vauthors=Camenga DR, Tindle HA |date=July 2018 |title=Weighing the Risks and Benefits of Electronic Cigarette Use in High-Risk Populations |journal=The Medical Clinics of North America |volume=102 |issue=4 |pages=765–779 |doi=10.1016/j.mcna.2018.03.002 |pmid=29933828 |s2cid=49389902}}{{cite journal |vauthors=Drope J, Cahn Z, Kennedy R, Liber AC, Stoklosa M, Henson R, Douglas CE, Drope J |date=November 2017 |title=Key issues surrounding the health impacts of electronic nicotine delivery systems (ENDS) and other sources of nicotine |journal=CA |volume=67 |issue=6 |pages=449–471 |doi=10.3322/caac.21413 |pmid=28961314 |doi-access=free}} Reviews in 2016{{cite journal |vauthors=Bhatnagar A |date=June 2016 |title=Cardiovascular Perspective of the Promises and Perils of E-Cigarettes |journal=Circulation Research |volume=118 |issue=12 |pages=1872–1875 |doi=10.1161/CIRCRESAHA.116.308723 |pmc=5505630 |pmid=27283531}} and 2018 claimed that the harm from e-cigarettes is much higher than the "95% safer" figure.

A 2025 RCP review{{Cite web |date=12 May 2016 |title=Promote e-cigarettes widely as substitute for smoking says new RCP report |url=https://www.rcp.ac.uk/news-and-media/news-and-opinion/promote-e-cigarettes-widely-as-substitute-for-smoking-says-new-rcp-report/ |access-date=2025-01-15 |website=www.rcp.ac.uk |language=en}} reported that e-cigarettes sold in England (which allow nicotine strength{{cite web |author=Katie Hunt |date=17 September 2019 |title=The US and UK see vaping very differently. Here's why |url=https://www.cnn.com/2019/09/17/health/vaping-us-uk-e-cigarette-differences-intl/index.html |website=CNN}} of no more than 20 mg/ml){{cite web |date=12 July 2022 |title=E-cigarettes: regulations for consumer products |url=https://www.gov.uk/guidance/e-cigarettes-regulations-for-consumer-products |website=GOV.UK |language=en}} are unlikely to exceed 5% of the harm of cigarettes for non-pregnant adults. This claim is consistent with the 2018 view of the US National Academies of Sciences, Engineering, and Medicine.{{Cite web|url=https://www.nap.edu/resource/24952/012318ecigaretteHighlights.pdf|title=Public Health Consequences of E-Cigarettes}}

Device defects can result in e.g., battery explosions and may cause burns or other injuries.{{cite journal |vauthors=Ebbert JO, Agunwamba AA, Rutten LJ |date=January 2015 |title=Counseling patients on the use of electronic cigarettes |journal=Mayo Clinic Proceedings |volume=90 |issue=1 |pages=128–134 |doi=10.1016/j.mayocp.2014.11.004 |pmid=25572196 |doi-access=free}}

Concentrated e-liquid exposure can come by leaks or spills.{{cite journal |vauthors=Yang L, Rudy SF, Cheng JM, Durmowicz EL |date=May 2014 |title=Electronic cigarettes: incorporating human factors engineering into risk assessments |journal=Tobacco Control |volume=23 |issue=Supplement 2 |pages=ii47–ii53 |doi=10.1136/tobaccocontrol-2013-051479 |pmc=3995290 |pmid=24732164}} Nicotine poisoning can occur by ingestion, inhalation, or absorption via the skin or eyes.{{cite journal |vauthors=Rom O, Pecorelli A, Valacchi G, Reznick AZ |date=March 2015 |title=Are E-cigarettes a safe and good alternative to cigarette smoking? |journal=Annals of the New York Academy of Sciences |volume=1340 |issue=1 |pages=65–74 |bibcode=2015NYASA1340...65R |doi=10.1111/nyas.12609 |pmid=25557889 |s2cid=26187171}}{{cite journal |vauthors=Kaisar MA, Prasad S, Liles T, Cucullo L |date=July 2016 |title=A decade of e-cigarettes: Limited research & unresolved safety concerns |journal=Toxicology |volume=365 |pages=67–75 |bibcode=2016Toxgy.365...67K |doi=10.1016/j.tox.2016.07.020 |pmc=4993660 |pmid=27477296}}

A 2018 review concluded that exposure to second-hand vapor can reduce lung function.{{cite journal |vauthors=Khan MS, Khateeb F, Akhtar J, Khan Z, Lal A, Kholodovych V, Hammersley J |date=March 2018 |title=Organizing pneumonia related to electronic cigarette use: A case report and review of literature |journal=The Clinical Respiratory Journal |volume=12 |issue=3 |pages=1295–1299 |doi=10.1111/crj.12775 |pmid=29392888 |s2cid=4316261}}

A 2015 review concluded that adverse effects are mostly associated with short-term use and the reported adverse effects decreased over time.{{cite journal |vauthors=Gualano MR, Passi S, Bert F, La Torre G, Scaioli G, Siliquini R |date=September 2015 |title=Electronic cigarettes: assessing the efficacy and the adverse effects through a systematic review of published studies |journal=Journal of Public Health |volume=37 |issue=3 |pages=488–497 |doi=10.1093/pubmed/fdu055 |pmid=25108741 |doi-access=free}}

Many effects on the nervous and the sensory systems are possibly related to nicotine overdose or withdrawal.{{cite journal |vauthors=Lauterstein D, Hoshino R, Gordon T, Watkins BX, Weitzman M, Zelikoff J |year=2014 |title=The changing face of tobacco use among United States youth |journal=Current Drug Abuse Reviews |volume=7 |issue=1 |pages=29–43 |doi=10.2174/1874473707666141015220110 |pmc=4469045 |pmid=25323124}} A 2016 study reported that an e-liquid containing 23% alcohol was linked to reduced performance on the Purdue Pegboard Test.{{cite journal |vauthors=MacLean RR, Valentine GW, Jatlow PI, Sofuoglu M |date=February 2017 |title=Inhalation of Alcohol Vapor: Measurement and Implications |journal=Alcoholism: Clinical and Experimental Research |volume=41 |issue=2 |pages=238–250 |doi=10.1111/acer.13291 |pmc=6143144 |pmid=28054395}} A 2017 study reported harm to neurons along with tremors and spasms.{{cite journal |vauthors=Qasim H, Karim ZA, Rivera JO, Khasawneh FT, Alshbool FZ |date=August 2017 |title=Impact of Electronic Cigarettes on the Cardiovascular System |journal=Journal of the American Heart Association |volume=6 |issue=9 |page=e006353 |doi=10.1161/JAHA.117.006353 |pmc=5634286 |pmid=28855171}}

File:Status_of_E-cigarette_at_Time_of_Fire.png (USFA) report entitled Electronic Cigarette Fires and Explosions. The USFA said that 25 fires and explosions in the US were the result of vaping between 2009 and August 2014.]]

E-cigarettes typically use lithium batteries, which may cause injury if defective{{cite web |year=2016 |title=Know the Risks |url=https://e-cigarettes.surgeongeneral.gov/knowtherisks.html |publisher=Surgeon General of the United States}}{{PD-notice}} or misused. A 2015 PHE report concluded that fire risks from e-cigarettes "appear to be comparable to similar electrical goods".{{rp|83–84}} A 2016 study reported that the explosion risk was low.{{cite journal |vauthors=Paley GL, Echalier E, Eck TW, Hong AR, Farooq AV, Gregory DG, Lubniewski AJ |date=July 2016 |title=Corneoscleral Laceration and Ocular Burns Caused by Electronic Cigarette Explosions |journal=Cornea |volume=35 |issue=7 |pages=1015–1018 |doi=10.1097/ICO.0000000000000881 |pmc=4900417 |pmid=27191672}}

E-liquid ingredients may be flammable.{{cite journal |vauthors=Weaver M, Breland A, Spindle T, Eissenberg T |year=2014 |title=Electronic cigarettes: a review of safety and clinical issues |journal=Journal of Addiction Medicine |volume=8 |issue=4 |pages=234–240 |doi=10.1097/ADM.0000000000000043 |pmc=4123220 |pmid=25089953}}

A 2014 review claimed that some users add more or larger batteries to nonadjustable e-cigarettes, which may lead to battery leakage or explosion.{{cite journal |vauthors=Rowell TR, Tarran R |date=December 2015 |title=Will chronic e-cigarette use cause lung disease? |journal=American Journal of Physiology. Lung Cellular and Molecular Physiology |volume=309 |issue=12 |pages=L1398–L1409 |doi=10.1152/ajplung.00272.2015 |pmc=4683316 |pmid=26408554}}

Another 2016 study assembled reports of 92 explosion, fire, or overheating events, with related injuries in 47 individuals.{{cite journal |vauthors=Vaught B, Spellman J, Shah A, Stewart A, Mullin D |date=March 2017 |title=Facial trauma caused by electronic cigarette explosion |journal=Ear, Nose, & Throat Journal |volume=96 |issue=3 |pages=139–142 |doi=10.1177/014556131709600314 |pmid=28346645 |doi-access=free}} Prominent harms included 2 cervical vertebral fractures, 1 palate fracture, 3 instances of damaged teeth, 33 thermal burns, 4 chemical burns, and 5 lacerations. A 2017 study reported that most e-cigarette fires are triggered by batteries overheating and igniting.{{cite book |url=https://www.nap.edu/resource/24952/012318ecigaretteHighlights.pdf |title=Public Health Consequences of E-Cigarettes |vauthors=Stratton K, Kwan LY, Eaton DL |date=January 2018 |publisher=National Academies of Sciences, Engineering, and Medicine (National Academies Press) |isbn=978-0-309-46834-3 |editor-last1=Stratton |editor-first1=Kathleen |pages=1–774 |doi=10.17226/24952 |pmid=29894118 |editor-last2=Kwan |editor-first2=Leslie Y. |editor-last3=Eaton |editor-first3=David L. |ref={{harvid|Stratton|2018}}}}{{rp|Summary, Conclusion 14-1.; 9}}{{cite journal |vauthors=Serror K, Chaouat M, Legrand MM, Depret F, Haddad J, Malca N, Mimoun M, Boccara D |date=May 2018 |title=Burns caused by electronic vaping devices (e-cigarettes): A new classification proposal based on mechanisms |journal=Burns |volume=44 |issue=3 |pages=544–548 |doi=10.1016/j.burns.2017.09.005 |pmid=29056367}} In 2018 PHE reported six UK case studies involving e-cigarettes with burns.{{rp|144}}

An e-cigarette explosion or fire can induce serious burns and harms.{{rp|149}}{{cite journal |vauthors=Patterson SB, Beckett AR, Lintner A, Leahey C, Greer A, Brevard SB, Simmons JD, Kahn SA |year=2017 |title=A Novel Classification System for Injuries After Electronic Cigarette Explosions |journal=Journal of Burn Care & Research |volume=38 |issue=1 |pages=e95–e100 |doi=10.1097/BCR.0000000000000471 |pmid=27893577 |s2cid=3433324}} Explosions have resulted in lost teeth, neck fractures, and burns from combustion and/or battery acid.{{cite journal |vauthors=Makadia LD, Roper PJ, Andrews JO, Tingen MS |date=August 2017 |title=Tobacco Use and Smoke Exposure in Children: New Trends, Harm, and Strategies to Improve Health Outcomes |journal=Current Allergy and Asthma Reports |volume=17 |issue=8 |page=55 |doi=10.1007/s11882-017-0723-0 |pmid=28741144 |s2cid=22360961}} Reported burns covered from 1% to 8% of body area. They were most commonly reported in the lower extremity, hands, head and neck, and genitalia.{{cite journal |vauthors=Harshman J, Vojvodic M, Rogers AD |date=October 2018 |title=Burns associated with e-cigarette batteries: A case series and literature review |journal=CJEM |volume=20 |issue=S2 |pages=S20–S28 |doi=10.1017/cem.2017.32 |pmid=28566106 |doi-access=free}} Explosions in some cases produced 2nd and 3rd degree burns.{{cite journal |vauthors=Hickey S, Goverman J, Friedstat J, Sheridan R, Schulz J |date=August 2018 |title=Thermal injuries from exploding electronic cigarettes |journal=Burns |volume=44 |issue=5 |pages=1294–1301 |doi=10.1016/j.burns.2018.02.008 |pmid=29503045 |s2cid=3709168}} A 2018 review concluded that some 50% needed surgical management.

A 2017 review observed that several reported injury cases occurred while the e-cigarette was carried in a pocket. The pocket may have sufficient moisture to start a chemical reaction within the lithium-ion battery, while the presence of metal objects can create a short-circuit, leading to an explosion.{{cite journal |vauthors=Arnaout A, Khashaba H, Dobbs T, Dewi F, Pope-Jones S, Sack A, Estela C, Nguyen D |date=June 2017 |title=The Southwest UK Burns Network (SWUK) experience of electronic cigarette explosions and review of literature |journal=Burns |volume=43 |issue=4 |pages=e1–e6 |doi=10.1016/j.burns.2017.01.008 |pmid=28412133}} Burn risk extends to bystanders.

alt=Graphic from a July 2016 [[United States Fire Administration (USFA) report entitled Electronic Cigarette Fires and Explosions in the United States 2009 – 2016. There has been an increase in the number of severe and moderate injuries resulting from e-cigarette explosions and fires since 2014. The USFA noted that this appears to correlate well with the e-cigarette sales trend.|thumb|Graphic from a July 2016 United States Fire Administration (USFA) report entitled Electronic Cigarette Fires and Explosions in the United States 2009 – 2016. There has been an increase in the number of severe and moderate injuries resulting from e-cigarette explosions and fires since 2014. The USFA noted that this appears to correlate well with the e-cigarette sales trend.]]

The United States Fire Administration reported 195 occasions of e-cigarette fires and explosions between January 2009 and December 2016. These incidents resulted in 133 acute injuries, of which 38 (29%) were severe. A 2017 review concluded that 80% of e-cigarette explosions occurred during battery charging, many by 3rd-party power adaptors that used inappropriately high charge rates that led to thermal runaway. Some vendors assembled e-cigarettes from incompatible parts.

File:Man_Smokes_Vapor_E_Cigarette_&_Explodes_on_Bus.ogg |vauthors=Caplan D}}]]

File:E-cigarette_explosion_burn.jpg

Burn events while on home oxygen therapy have been reported, leading Health Canada in 2014 to warn of fire risk. The heating element in vaping devices can get hot enough to ignite in the presence of oxygen.{{cite journal |vauthors=Lacasse Y, Légaré M, Maltais F |year=2015 |title=E-cigarette use in patients receiving home oxygen therapy |journal=Canadian Respiratory Journal |volume=22 |issue=2 |pages=83–85 |doi=10.1155/2015/215932 |pmc=4390016 |pmid=25848719 |doi-access=free}}{{CC-notice|cc=by4|url=https://www.hindawi.com/journals/crj/2015/215932/abs/|author(s)=Yves Lacasse, Martin Légaré, and François Maltais}}

File:Symptoms_of_nicotine_poisoning.png related to e-cigarette calls to US poison control centersDetailed reference list is located at a separate image page.]]

E-cigaratte nicotine poisoning occurs via ingestion, inhalation, or absorption via the skin or eyes.

Such poisoning is apparently rare, suggested by the fact that reviews highlight individual cases. In 2014, an infant died from choking on an e-cigarette component.{{cite journal |vauthors=Jo CL, Ambs A, Dresler CM, Backinger CL |date=February 2017 |title=Child-resistant and tamper-resistant packaging: A systematic review to inform tobacco packaging regulation |journal=Preventive Medicine |volume=95 |pages=89–95 |doi=10.1016/j.ypmed.2016.11.013 |pmc=5299541 |pmid=27939602}} As of 2016 four adults were reported to have died in the US and Europe after intentionally ingesting e-liquid.{{cite journal |vauthors=Hua M, Talbot P |date=December 2016 |title=Potential health effects of electronic cigarettes: A systematic review of case reports |journal=Preventive Medicine Reports |volume=4 |pages=169–178 |doi=10.1016/j.pmedr.2016.06.002 |pmc=4929082 |pmid=27413679}}{{CC-notice|cc=by4|url=http://www.sciencedirect.com/science/article/pii/S2211335516300523?via%3Dihub|vauthors=Hua M, Talbot P}} Two children, one in the US in 2014 and another in Israel in 2013, died after ingesting liquid nicotine.{{cite journal |vauthors=Biyani S, Derkay CS |date=August 2015 |title=E-cigarettes: Considerations for the otolaryngologist |journal=International Journal of Pediatric Otorhinolaryngology |volume=79 |issue=8 |pages=1180–1183 |doi=10.1016/j.ijporl.2015.04.032 |pmid=25998217}} A two-year-old girl in the UK in 2014 was hospitalized after licking an e-cigarette liquid refill.{{cite journal |vauthors=Kim KH, Kabir E, Jahan SA |date=October 2016 |title=Review of electronic cigarettes as tobacco cigarette substitutes: Their potential human health impact |journal=Journal of Environmental Science and Health. Part C, Environmental Carcinogenesis & Ecotoxicology Reviews |volume=34 |issue=4 |pages=262–275 |bibcode=2016JESHC..34..262K |doi=10.1080/10590501.2016.1236604 |pmid=27635466 |s2cid=42660975}}

A 2022 concluded that toxicity can come from aerosols containing toxic chemicals{{Cite journal |last1=Gordon |first1=Terry |last2=Karey |first2=Emma |last3=Rebuli |first3=Meghan E. |last4=Escobar |first4=Yael-Natalie H. |last5=Jaspers |first5=Ilona |last6=Chen |first6=Lung Chi |date=2022-01-06 |title=E-Cigarette Toxicology |journal=Annual Review of Pharmacology and Toxicology |volume=62 |pages=301–322 |doi=10.1146/annurev-pharmtox-042921-084202 |issn=0362-1642 |pmc=9386787 |pmid=34555289}} or excessive concentrations of nicotine as an e-liquid.

A 2014 review concluded that users may alter e-liquid contents, adding substances such as alcohol or nicotine, possibly making them toxic.

As of 2014, calls to US poison control centers involved inhalations, eye exposures, skin exposures, and ingestion, in both adults and children.{{cite journal |vauthors=Chatham-Stephens K, Law R, Taylor E, Melstrom P, Bunnell R, Wang B, Apelberg B, Schier JG |date=April 2014 |title=Notes from the field: calls to poison centers for exposures to electronic cigarettes--United States, September 2010-February 2014 |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6313a4.htm |journal=MMWR. Morbidity and Mortality Weekly Report |volume=63 |issue=13 |pages=292–293 |pmc=5779356 |pmid=24699766}} A 2016 study reported minor, moderate, and serious adverse effects.{{cite journal |vauthors=Chatham-Stephens K, Law R, Taylor E, Kieszak S, Melstrom P, Bunnell R, Wang B, Day H, Apelberg B, Cantrell L, Foster H, Schier JG |date=December 2016 |title=Exposure Calls to U. S. Poison Centers Involving Electronic Cigarettes and Conventional Cigarettes-September 2010-December 2014 |journal=Journal of Medical Toxicology |volume=12 |issue=4 |pages=350–357 |doi=10.1007/s13181-016-0563-7 |pmc=5135675 |pmid=27352081}} Minor effects correlated with e-liquid poisoning were tachycardia, tremor, chest pain and hypertension. More serious effects were bradycardia, hypotension, nausea, respiratory paralysis, atrial fibrillation and dyspnea.{{cite journal |vauthors=Nelluri BK, Murphy K, Mookadam F |date=May 2015 |title=Electronic cigarettes and cardiovascular risk: hype or up in smoke? |journal=Future Cardiology |volume=11 |issue=3 |pages=271–273 |doi=10.2217/fca.15.13 |pmid=26021631 |doi-access=free}} Initial symptoms included rapid heart rate, sweating, feeling sick, and vomiting. Delayed symptoms included low blood pressure, seizures, and hypoventilation.{{cite web |date=20 October 2014 |title=Young Children and e-Cigarette Poisoning |url=http://www.medscape.com/viewarticle/832938 |publisher=Medscape |vauthors=Chatham-Stephens K}} Rare serious effects included coma, seizure, trouble breathing, and heart attack.{{cite journal |vauthors=Govindarajan P, Spiller HA, Casavant MJ, Chounthirath T, Smith GA |date=May 2018 |title=E-Cigarette and Liquid Nicotine Exposures Among Young Children |journal=Pediatrics |volume=141 |issue=5 |page=e20173361 |doi=10.1542/peds.2017-3361 |pmid=29686144 |doi-access=free}} After examining poison control centers' reports between 2010 and early 2019, FDA reported that, between the poison control centers and FDA, 35 cases of seizures mentioned use of e-cigarettes.{{cite web |date=3 April 2019 |title=Some E-cigarette Users Are Having Seizures, Most Reports Involving Youth and Young Adults |url=https://www.fda.gov/TobaccoProducts/NewsEvents/ucm635133.htm |archive-url=https://web.archive.org/web/20190403235054/https://www.fda.gov/TobaccoProducts/NewsEvents/ucm635133.htm |url-status=dead |archive-date=3 April 2019 |publisher=United States Food and Drug Administration}}{{PD-notice}}

From 2011 to 2019, cases of accidental poisoning from nicotine e-liquids grew rapidly in the US.{{cite journal |vauthors=Jenssen BP, Walley SC |date=February 2019 |title=E-Cigarettes and Similar Devices |journal=Pediatrics |volume=143 |issue=2 |page=e20183652 |doi=10.1542/peds.2018-3652 |pmc=6644065 |pmid=30835247}} From 1 September 2010, to 31 December 2014, 58% of e-cigarette calls to US poison control centers were related to children under 6. In 2014 Centers for Disease Control and Prevention (CDC) reported that 51.1% of the calls to US poison centers due to e-cigarettes were related to children under age 5, and while 42% of calls were related to people age 20 and older.{{cite web |date=3 April 2014 |title=New CDC study finds dramatic increase in e-cigarette-related calls to poison centers |url=https://www.cdc.gov/media/releases/2014/p0403-e-cigarette-poison.html |publisher=Centers for Disease Control and Prevention}}{{PD-notice}} E-cigarette calls had a greater chance to report an adverse effect and a greater chance to report a moderate or major adverse effect than traditional cigarette calls.{{Clarify|date=January 2025}} Severe outcomes were more than 2.5 times more frequent in children exposed to e-cigarettes and nicotine e-liquid than with traditional cigarettes.{{cite journal |vauthors=Kamboj A, Spiller HA, Casavant MJ, Chounthirath T, Smith GA |date=June 2016 |title=Pediatric Exposure to E-Cigarettes, Nicotine, and Tobacco Products in the United States |journal=Pediatrics |volume=137 |issue=6 |page=e20160041 |doi=10.1542/peds.2016-0041 |pmid=27244861 |doi-access=free}}

File:CDC_E-cigs-poison.jpg

US poison control centers reported that 92.5% of children who came in contact with nicotine e-liquid swallowed it during the period from January 2012 to April 2017.

In 2016 American Association of Poison Control Centers (AAPCC) reported 2,907 exposures regarding e-cigarettes and liquid nicotine.{{cite web |year=2018 |title=E-Cigarettes and Liquid Nicotine |url=https://aapcc.org/track/ecigarettes-liquid-nicotine |publisher=American Association of Poison Control Centers}} The yearly nicotine exposure rate in the US involving children went up by 1,398% from 2012 to 2015, later dropping by 20% from 2015 to 2016. In 2017 the National Poison Data System stated that exposures to e-cigarettes and liquid nicotine among young children was rising significantly.{{cite journal |vauthors=Peterson LA, Hecht SS |date=April 2017 |title=Tobacco, e-cigarettes, and child health |journal=Current Opinion in Pediatrics |volume=29 |issue=2 |pages=225–230 |doi=10.1097/MOP.0000000000000456 |pmc=5598780 |pmid=28059903}}

As of 2015, the long-term lung function effects of vaping were unknown.{{cite journal |vauthors=Orellana-Barrios MA, Payne D, Mulkey Z, Nugent K |date=July 2015 |title=Electronic Cigarettes—A Narrative Review for Clinicians |journal=The American Journal of Medicine |volume=128 |issue=7 |pages=674–681 |doi=10.1016/j.amjmed.2015.01.033 |pmid=25731134 |doi-access=free}}{{rp|12}} A 2014 study reported that limited evidence suggests that e-cigarettes produce less short-term effects on lung function than traditional cigarettes.{{cite journal |vauthors=Drummond MB, Upson D |date=February 2014 |title=Electronic cigarettes. Potential harms and benefits |journal=Annals of the American Thoracic Society |volume=11 |issue=2 |pages=236–242 |doi=10.1513/annalsats.201311-391fr |pmc=5469426 |pmid=24575993}} As of 2015 many e-liquid ingredients had not been examined in the lung.

E-cigarettes are associated with asthma and other respiratory diseases.{{Cite journal |last=Xie |first=Wubin |last2=Kathuria |first2=Hasmeena |last3=Galiatsatos |first3=Panagis |last4=Blaha |first4=Michael J. |last5=Hamburg |first5=Naomi M. |last6=Robertson |first6=Rose Marie |last7=Bhatnagar |first7=Aruni |last8=Benjamin |first8=Emelia J. |last9=Stokes |first9=Andrew C. |date=2020-11-02 |title=Association of Electronic Cigarette Use With Incident Respiratory Conditions Among US Adults From 2013 to 2018 |url=https://pubmed.ncbi.nlm.nih.gov/33180127 |journal=JAMA network open |volume=3 |issue=11 |pages=e2020816 |doi=10.1001/jamanetworkopen.2020.20816 |issn=2574-3805 |pmc=7662143 |pmid=33180127}}

A 2015 review concluded that e-cigarettes may induce acute lung disease.

A 2018 study reported correlations between vaping and pleural effusions.{{cite journal |vauthors=Wyman AE, Hines SE |date=April 2018 |title=Update on metal-induced occupational lung disease |journal=Current Opinion in Allergy and Clinical Immunology |volume=18 |issue=2 |pages=73–79 |doi=10.1097/ACI.0000000000000420 |pmid=29337701 |s2cid=3613573}} A 2015 study reported that e-cigarette vapors can induce oxidative stress in lung endothelial cells. A 2016 review concluded that e-cigarette vapor that triggered constant lung inflammation could result in lung pathogenesis and induce diseases such as chronic obstructive pulmonary disease and fibrosis. A 2018 review concluded that e-cigarette vapors can result in acute endothelial cell injury, but the long-term effects were uncertain.{{rp|Summary, 7}} A 2017 review concluded "Exposure to nicotine that was specifically generated by the use of e-cigarettes, was shown to promote oxidative stress and impairment of autophagy, which in turn serves as a potential mechanism leading to development of chronic obstructive pulmonary disease."{{cite journal |vauthors=Cai H, Wang C |date=October 2017 |title=Graphical review: The redox dark side of e-cigarettes; exposure to oxidants and public health concerns |journal=Redox Biology |volume=13 |pages=402–406 |doi=10.1016/j.redox.2017.05.013 |pmc=5493817 |pmid=28667909}} A 2014 case report observed the correlation between sub-acute bronchiolitis and vaping. After quitting vaping the symptoms improved. Vaping causes bronchospasm. Adolescents who vaped had a higher frequency of chronic bronchitis symptoms.{{cite journal |vauthors=Shields PG, Berman M, Brasky TM, Freudenheim JL, Mathe E, McElroy JP, Song MA, Wewers MD |date=August 2017 |title=A Review of Pulmonary Toxicity of Electronic Cigarettes in the Context of Smoking: A Focus on Inflammation |journal=Cancer Epidemiology, Biomarkers & Prevention |volume=26 |issue=8 |pages=1175–1191 |doi=10.1158/1055-9965.EPI-17-0358 |pmc=5614602 |pmid=28642230}}

A 2015 review reported that the long-term effects regarding respiratory flow resistance were unknown. A 2014 review concluded that e-cigarettes reduced lung function, but much less than traditional cigarettes.{{cite journal |vauthors=Harrell PT, Simmons VN, Correa JB, Padhya TA, Brandon TH |date=September 2014 |title=Electronic nicotine delivery systems ("e-cigarettes"): review of safety and smoking cessation efficacy |journal=Otolaryngology–Head and Neck Surgery |volume=151 |issue=3 |pages=381–393 |doi=10.1177/0194599814536847 |pmc=4376316 |pmid=24898072}} A 2015 clinician's guide stated that 5 minutes of vaping considerably increased lung airflow resistance. A 2013 review concluded that a single e-cigarette increased airway resistance.{{cite journal |vauthors=Bertholon JF, Becquemin MH, Annesi-Maesano I, Dautzenberg B |year=2013 |title=Electronic cigarettes: a short review |journal=Respiration; International Review of Thoracic Diseases |volume=86 |issue=5 |pages=433–438 |doi=10.1159/000353253 |pmid=24080743 |s2cid=20521181 |doi-access=free}}

A 2014 study reported higher levels of exhaled nitric oxide, which was associated with lung inflammation.{{cite journal |vauthors=Zainol Abidin N, Zainal Abidin E, Zulkifli A, Karuppiah K, Syed Ismail SN, Amer Nordin AS |date=September 2017 |title=Electronic cigarettes and indoor air quality: a review of studies using human volunteers |url=http://psasir.upm.edu.my/id/eprint/61699/1/Electronic%20cigarettes%20and%20indoor%20air%20quality.pdf |journal=Reviews on Environmental Health |volume=32 |issue=3 |pages=235–244 |doi=10.1515/reveh-2016-0059 |pmid=28107173 |bibcode=2017RvEH...32..235Z |s2cid=6885414}} A 2014 review concluded that harmful effects to cardiovascular and respiratory functions after short-term use of e-cigarettes were appreciably milder than traditional cigarettes. A 2015 review concluded that short-term use increased respiratory resistance compared to traditional cigarettes.

A 2018 study reported that adolescent vapers with asthma or other respiratory ailments could have greater odds of increasing respiratory symptoms and aggravations.{{rp|Vulnerable/Susceptible Populations, Cystic Fibrosis; 448}} In 2018 PHE reported "There have been some studies with adolescents suggesting respiratory symptoms among EC experimenters. However, small scale or uncontrolled switching studies from smoking to vaping have demonstrated some respiratory improvements."{{{rp|174}} A 2017 review concluded "among a population of 11th-grade and 12th-grade students in California, vaping was associated with twice the risk of respiratory symptoms, and the risk increased with more frequent e-cigarette use."{{cite journal |vauthors=Barraza LF, Weidenaar KE, Cook LT, Logue AR, Halpern MT |date=August 2017 |title=Regulations and policies regarding e-cigarettes |journal=Cancer |volume=123 |issue=16 |pages=3007–3014 |doi=10.1002/cncr.30725 |pmid=28440949 |s2cid=45269159 |doi-access=free}}

E-cigarette particles are small enough to enter the alveoli and to go deep in the lungs and enter into systemic circulation. A 2017 study reported that vapor containing particulate matter with a diameter of 2.5 μm enters the circulation via the cardiopulmonary system, with a large deposit in the respiratory tract. A 2014 review concluded that metal nanoparticles can deposit in the alveolar sacs with possible pulmonary toxicity. A 2015 study reported that particle sizes differ across devices with impacts on respiratory tract depositions, and without regard to e-liquid.{{cite journal |vauthors=Collaco JM, Drummond MB, McGrath-Morrow SA |date=February 2015 |title=Electronic cigarette use and exposure in the pediatric population |journal=JAMA Pediatrics |volume=169 |issue=2 |pages=177–182 |doi=10.1001/jamapediatrics.2014.2898 |pmc=5557497 |pmid=25546699}}

A 2019 case study of hard-metal pneumoconiosis cannabis vapers reported cobalt, nickel, aluminum, manganese, lead, and chromium in the vapor. Metal-induced toxicity in the lung can result in long-term/permanent lung scarring.{{cite journal |vauthors=Boudi FB, Patel S, Boudi A, Chan C |date=December 2019 |title=Vitamin E Acetate as a Plausible Cause of Acute Vaping-related Illness |journal=Cureus |volume=11 |issue=12 |pages=e6350 |doi=10.7759/cureus.6350 |pmc=6952050 |pmid=31938636 |doi-access=free}}{{CC-notice|cc=by3|url=https://www.cureus.com/articles/25498-vitamin-e-acetate-as-a-plausible-cause-of-acute-vaping-related-illness|author(s)=F Brian Boudi, Sonia Patel, Ava Boudi, Connie Chan}}

A 2018 review concluded that exposure to vapor has adverse effects on lungs and pulmonary function. Repeated acrolein exposure causes chronic pulmonary inflammation, reduction of host defense, neutrophil inflammation, mucus hypersecretion, and protease-mediated lung tissue damage, which are linked to the development of chronic obstructive pulmonary disease (COPD). Although e-cigarette aerosol also exposes users to highly oxidizing free radicals, their chemical characteristics is unclear.{{cite journal |vauthors=Benowitz NL, Fraiman JB |date=August 2017 |title=Cardiovascular effects of electronic cigarettes |journal=Nature Reviews. Cardiology |volume=14 |issue=8 |pages=447–456 |doi=10.1038/nrcardio.2017.36 |pmc=5519136 |pmid=28332500}}

It further reported that vapers experienced decreased expression of immune-related genes in their nasal cavities, more so than smokers. By contrast, vaping upregulates expression of platelet-activating factor receptor (PAFR) in nasal epithelial cells; PAFR is an important molecule involved in the ability of S. pneumoniae, (leading cause of bacterial pneumonia), to attach to cells.

A 2020 study reported that vaping led to lung injuries that include hypersensitivity pneumonitis (HP), diffuse alveolar hemorrhage (DAH), acute eosinophilic pneumonia (AEP), diffuse alveolar damage, organizing pneumonia (OP), lipoid pneumonia, and giant cell interstitial pneumonia (GIP).{{cite journal |vauthors=Henry TS, Kligerman SJ, Raptis CA, Mann H, Sechrist JW, Kanne JP |date=March 2020 |title=Imaging Findings of Vaping-Associated Lung Injury |journal=AJR. American Journal of Roentgenology |volume=214 |issue=3 |pages=498–505 |doi=10.2214/AJR.19.22251 |pmid=31593518 |s2cid=203985885}}

A 2016 study reported that adverse effects may include airway resistance, irritation of the airways, eyes redness, dry throat,{{cite journal |vauthors=Singh J, Luquet E, Smith DP, Potgieter HJ, Ragazzon P |date=December 2016 |title=Toxicological and analytical assessment of e-cigarette refill components on airway epithelia |url=https://e-space.mmu.ac.uk/617844/1/E-cigarette%20paper%20Revis%201.pdf |journal=Science Progress |volume=99 |issue=4 |pages=351–398 |doi=10.3184/003685016X14773090197706 |pmc=10365464 |pmid=28742478 |s2cid=4573125}} and increase in allergic airway inflammation with elevated infiltration of inflammatory cells including eosinophils into airways. A 2015 study reported that the most reported short-term adverse effects were mouth and throat irritation, dry cough, and nausea. Another 2016 study reported nose bleeds, change in bronchial gene expression, release of cytokines and proinflammatory mediators.

A 2016 review concluded that nicotine exposure harms youths' growing brains.{{cite journal |vauthors=Greenhill R, Dawkins L, Notley C, Finn MD, Turner JJ |date=December 2016 |title=Adolescent Awareness and Use of Electronic Cigarettes: A Review of Emerging Trends and Findings |journal=The Journal of Adolescent Health |volume=59 |issue=6 |pages=612–619 |doi=10.1016/j.jadohealth.2016.08.005 |pmid=27693128 |doi-access=free}} Vaping is associated with a positive association of vaping and chronic bronchitis among US high school juniors and seniors; which persisted among former users. Vaping was associated with an increased diagnosis of asthma and asthma-related school absences among Korean never-smoker high school students. A 2018 review concluded that child vapers had a higher likelihood of more and more significant adverse effects than child smokers. Significant harmful effects included cyanosis, nausea, and coma.{{cite journal |vauthors=Lødrup Carlsen KC, Skjerven HO, Carlsen KH |date=September 2018 |title=The toxicity of E-cigarettes and children's respiratory health |journal=Paediatric Respiratory Reviews |volume=28 |pages=63–67 |doi=10.1016/j.prrv.2018.01.002 |pmid=29580719 |s2cid=4368058}}

A 2020/21 survey of 39,214 young people (aged 16 to 19) from the US, Canada, and England found that those who vaped were more likely to have breathing issues (breathlessness, wheezing, chest pain, phlegm, and cough) than those who did not. Also, the more young people vaped, the higher their chance of breathing issues.{{Cite journal |last1=Brose |first1=Leonie S. |last2=Reid |first2=Jessica L. |last3=Robson |first3=Debbie |last4=McNeill |first4=Ann |last5=Hammond |first5=David |date=2024-05-29 |title=Associations between vaping and self-reported respiratory symptoms in young people in Canada, England and the US |journal=BMC Medicine |volume=22 |issue=1 |pages=213 |doi=10.1186/s12916-024-03428-6 |doi-access=free |issn=1741-7015 |pmc=11134717 |pmid=38807205}}{{Cite journal |date=11 March 2025 |title=Vaping is linked with breathing issues in young people |url=https://evidence.nihr.ac.uk/alert/vaping-is-linked-with-breathing-issues-in-young-people/ |journal=NIHR Evidence}}

{{excerpt|2019–2020 vaping lung illness outbreak}}

A 2018 review concluded that the specific role of nicotine in cardiovascular disease had not been established.

A 2023 review concluded that vaping causes significant, potentially harmful effects on many cardiovascular parameters.{{cite journal |vauthors=Siddiqi TJ, Rashid AM, Siddiqi AK, Anwer A, Usman MS, Sakhi H, Bhatnagar A, Hamburg NM, Hirsch GA, Rodriguez CJ, Blaha MJ, DeFilippis AP, Benjamin EJ, Hall ME |date=September 2023 |title=Cardiovascular effects of electronic cigarettes: A systematic review and meta-analysis |journal=Current Problems in Cardiology |volume=48 |issue=9 |page=101748 |doi=10.1016/j.cpcardiol.2023.101748 |pmid=37088177 |doi-access=free}} A 2024 review attributed cardiovascular effects to oxidative stress, inflammation, endothelial dysfunction, atherosclerosis, hemodynamic effects, and platelet function.{{cite journal |vauthors=Zong H, Hu Z, Li W |date=20 February 2024 |title=Electronic cigarettes and cardiovascular disease: epidemiological and biological links |journal=European Journal of Physiology |volume=476 |issue=6 |pages=875–888 |doi=10.1007/s00424-024-02925-0 |pmc=11139732 |pmid=38376568 |doi-access=free}} A 2019 review reported limited evidence of vaping's adverse impacts on endothelial function and arterial hardening.{{cite journal |vauthors=Skotsimara G, Antonopoulos AS, Oikonomou E, Siasos G, Ioakeimidis N, Tsalamandris S, Charalambous G, Galiatsatos N, Vlachopoulos C, Tousoulis D |date=July 2019 |title=Cardiovascular effects of electronic cigarettes: A systematic review and meta-analysis |journal=European Journal of Preventive Cardiology |volume=26 |issue=11 |pages=1219–1228 |doi=10.1177/2047487319832975 |pmid=30823865 |s2cid=73506976}} A 2017 review concluded that vaping could exacerbate adverse cardiovascular effects among those who already have cardiovascular disease. Studies of aldehydes, particulates, and flavorings reported mixed impacts on cardiovascular health. A 2017 review stated that low amounts of aldehydes are a health concern, particularly among individuals with cardiovascular disease. A 2014 review concluded that while vaping reduces cardiac muscle function and increases inflammation, these changes were non-significant. A 2017 review concluded that vapor particles can enter circulation via the airways.

Many vapor components impact atherosclerosis.{{cite journal |vauthors=Knura M, Dragon J, Łabuzek K, Okopień B |date=January 2018 |title=The impact of electronic cigarettes usage on the endothelial function and the progression of atherosclerosis |journal=Polski Merkuriusz Lekarski |volume=44 |issue=259 |pages=26–30 |pmid=29374420}} Case reports from 2014 documented possible cardiovascular adverse effects, mostly via improper use. However, these effects were reduced compared to traditional cigarettes.{{cite journal |vauthors=Lippi G, Favaloro EJ, Meschi T, Mattiuzzi C, Borghi L, Cervellin G |date=February 2014 |title=E-cigarettes and cardiovascular risk: beyond science and mysticism |journal=Seminars in Thrombosis and Hemostasis |volume=40 |issue=1 |pages=60–65 |doi=10.1055/s-0033-1363468 |pmid=24343348 |doi-access=free}}

A 2016 review concluded that vaping generates sympathomimetic effects.{{cite journal |vauthors=Nelluri B, Murphy K, Mookadam F, Mookadam M |date=March 2016 |title=The current literature regarding the cardiovascular effects of electronic cigarettes |journal=Future Cardiology |volume=12 |issue=2 |pages=167–179 |doi=10.2217/fca.15.83 |pmid=26916427}} A 2016 review concluded that there could be a risk for conditions such as tachycardia-induced cardiomyopathy. A 20154 clinician's review reported that short-term effects included increases in blood pressure and heart rate. A 2017 review concluded that these increases among smokers who vaped was lower than with smoking. A 2016 study reported vaping increased aortic stiffness in people with no cardiovascular risk factors, an d that the increase was lower than smoking. A 2017 review concluded that habitual vaping was associated with oxidative stress and a shift towards cardiac sympathetic activity, which are both associated with a risk of developing cardiovascular disease. A 2017 review highlighted an association between 2.5 μm particulate exposure and cardiovascular disease.

A 2018 review noted that nicotine is not the only biologically active component in e-cigarette aerosol. Vapor particles are of broadly similar size to those in traditional cigarettes. These particles can be biologically active, trigger inflammatory processes, and are directly implicated in causing cardiovascular disease and acute cardiovascular events. Their dose-response effect is nonlinear, with substantial increases in cardiovascular risk with even low exposure levels. Vapor induces platelet activation, aggregation, and adhesion, which are associated with increased cardiovascular risk. These changes produce rapid deterioration of vascular function. E-cigarette and traditional cigarette smoking in individuals with no known cardiovascular disease exhibit similar inhibition of artery dilation in response to the need for more blood flow. This change reflects damage to vascular endothelium and increases the risk of long-term heart disease and an acute event such as a myocardial infarction (heart attack). Vaping is accompanied by a shift in balance of the autonomic (reflex) nervous system toward sympathetic predominance, which is also associated with increased cardiac risk. Daily vaping is correlated with an increased risk of myocardial infarction in health surveys.

A 2015 doctor guide mentioned major adverse events that included hospitalizations for pneumonia, congestive heart failure, seizure, rapid heart rate, and burns. However, no causal relationship to vaping was proven.

A mucosal intestinal barrier separates the external and internal environments within the body. This barrier allows water, ions, solutes, and nutrients to cross the barrier while excluding bacteria and toxins.{{Cite journal |last=Turner |first=Jerrold R. |date=November 2009 |title=Intestinal mucosal barrier function in health and disease |url=https://www.nature.com/articles/nri2653 |journal=Nature Reviews Immunology |language=en |volume=9 |issue=11 |pages=799–809 |doi=10.1038/nri2653 |issn=1474-1741 |pmid=19855405|url-access=subscription }} Tight junctions (TJ) help with the construction and permeability of the barrier in the gut by firmly securing joints.{{Cite journal |last1=Oshima |first1=Tadayuki |last2=Miwa |first2=Hiroto |date=August 2016 |title=Gastrointestinal mucosal barrier function and diseases |journal=Journal of Gastroenterology |volume=51 |issue=8 |pages=768–778 |doi=10.1007/s00535-016-1207-z |issn=1435-5922 |pmid=27048502}} Chronic, repetitive exposure to e-cigarettes damages this barrier by breaking the TJs, which causes gut inflammation, assage of bacteria.{{Cite journal |last1=Sharma |first1=Aditi |last2=Lee |first2=Jasper |last3=Fonseca |first3=Ayden G. |last4=Moshensky |first4=Alex |last5=Kothari |first5=Taha |last6=Sayed |first6=Ibrahim M. |last7=Ibeawuchi |first7=Stella-Rita |last8=Pranadinata |first8=Rama F. |last9=Ear |first9=Jason |last10=Sahoo |first10=Debashis |last11=Crotty-Alexander |first11=Laura E. |last12=Ghosh |first12=Pradipta |last13=Das |first13=Soumita |date=2021-01-06 |title=E-cigarettes compromise the gut barrier and trigger inflammation |journal=iScience |volume=24 |issue=2 |page=102035 |bibcode=2021iSci...24j2035S |doi=10.1016/j.isci.2021.102035 |issn=2589-0042 |pmc=7841355 |pmid=33537654}} altering gene expression. A 2021 study reported that chronic use of nicotine-free e-cigarettes still caused inflammation and decreased TJ markers.{{Cite journal |last1=Sharma |first1=Aditi |last2=Lee |first2=Jasper |last3=Fonseca |first3=Ayden |last4=Crotty-Alexander |first4=Laura |last5=Ghosh |first5=Pradipta |date=19 February 2021 |title=E-cigarettes compromise the gut barrier and trigger inflammation |journal=iScience |volume=24 |issue=2 |bibcode=2021iSci...24j2035S |doi=10.1016/j.isci.2021.102035 |pmc=7841355 |pmid=33537654}}

A 2022 study reported that common GI health effects include nausea, vomiting, gastrointestinal discomfort, xerostomia, oral mucositis, gum bleeding, gingivitis, gastric burning, altered bowel habits, and acid reflux. Chronic exposure also drives inflammation in the colon.{{Cite journal |last1=Debnath |first1=Madhurima |last2=Debnath |first2=Dipanjan |last3=Singh |first3=Pratiksha |last4=Wert |first4=Yijin |last5=Nookala |first5=Vinod |date=24 July 2022 |title=Effect of Electronic Cigarettes on the Gastrointestinal System |journal=Cureus |volume=14 |issue=7 |page=e27210 |doi=10.7759/cureus.27210 |issn=2168-8184 |pmc=9322142 |pmid=35903484 |doi-access=free}}

A 2024 review concluded that nicotine exposure has detrimental effects on the nervous system, especially during adolescence. Exposure during developmental stages changes brain structure and function. Vaping is linked to impairment of cognitive processes, increased mood disorders and addiction, damage to functions such as memory, reasoning, impulse control, and attention.{{Cite journal |last1=López-Ojeda |first1=Wilfredo |last2=Hurley |first2=Robin A. |date=January 2024 |title=Vaping and the Brain: Effects of Electronic Cigarettes and E-Liquid Substances |url=https://psychiatryonline.org/doi/full/10.1176/appi.neuropsych.20230184 |journal=The Journal of Neuropsychiatry and Clinical Neurosciences |volume=36 |issue=1 |pages=A5–5 |doi=10.1176/appi.neuropsych.20230184 |issn=0895-0172 |pmid=38226910|url-access=subscription }} A 202 study reported lower gene expression, reducing occludin, which compromises the stability and strength of the blood-brain-barrier, resulting in neurovascular dysfunction, neuroinflammation, and cognitive defects.{{Cite journal |last1=Heldt |first1=Nathan A. |last2=Seliga |first2=Alecia |last3=Winfield |first3=Malika |last4=Gajghate |first4=Sachin |last5=Reichenbach |first5=Nancy |last6=Yu |first6=Xiang |last7=Rom |first7=Slava |last8=Tenneti |first8=Amogha |last9=May |first9=Dana |last10=Gregory |first10=Brian D. |last11=Persidsky |first11=Yuri |date=August 2020 |title=Electronic cigarette exposure disrupts blood-brain barrier integrity and promotes neuroinflammation |journal=Brain, Behavior, and Immunity |volume=88 |pages=363–380 |doi=10.1016/j.bbi.2020.03.034 |issn=1090-2139 |pmc=7899242 |pmid=32243899}} A 2010 study reported that short-term nicotine use excites the autonomic ganglia nerves and autonomic nerves.{{cite journal |vauthors=Toda N, Toda H |date=December 2010 |title=Nitric oxide-mediated blood flow regulation as affected by smoking and nicotine |journal=European Journal of Pharmacology |volume=649 |issue=1–3 |pages=1–13 |doi=10.1016/j.ejphar.2010.09.042 |pmid=20868673}}

A 2018 review reported little evidence indicating that vaping is less damaging than smoking for periodontal disease{{rp|Summary, Conclusion 12-1.; 9}} and can lead to increased risk of periodontal disease.{{cite journal |vauthors=Javed F, Kellesarian SV, Sundar IK, Romanos GE, Rahman I |date=November 2017 |title=Recent updates on electronic cigarette aerosol and inhaled nicotine effects on periodontal and pulmonary tissues |journal=Oral Diseases |volume=23 |issue=8 |pages=1052–1057 |doi=10.1111/odi.12652 |pmc=5545167 |pmid=28168771}} j A 2017 review concluded that nicotine and flavorings may damage periodontal ligaments, stem cells, and gingival fibroblasts in cultures from aldehydes and/or carbonyls from vapor. A 2016 clinicians guide state that e-cigarettes could harm the periodontium because of the effects of nicotine on gum tissues and the immune system.{{cite journal |vauthors=Chaffee BW, Couch ET, Ryder MI |date=June 2016 |title=The tobacco-using periodontal patient: role of the dental practitioner in tobacco cessation and periodontal disease management |journal=Periodontology 2000 |volume=71 |issue=1 |pages=52–64 |doi=10.1111/prd.12120 |pmc=4842013 |pmid=27045430}} A 2021 study reported that vaping resulted in nicotine stomatitis, hairy tongue, angular cheilitis,{{cite journal |vauthors=Sultan AS, Jessri M, Farah CS |date=March 2021 |title=Electronic nicotine delivery systems: Oral health implications and oral cancer risk |journal=Journal of Oral Pathology & Medicine |volume=50 |issue=3 |pages=316–322 |doi=10.1111/jop.12810 |pmid=30507043 |s2cid=54527046}} and oral mucosal lesions.{{cite journal |vauthors=Visconti MJ, Ashack KA |date=October 2019 |title=Dermatologic manifestations associated with electronic cigarette use |journal=Journal of the American Academy of Dermatology |volume=81 |issue=4 |pages=1001–1007 |doi=10.1016/j.jaad.2019.03.088 |pmid=30965061 |s2cid=106409405}} E-cigarettes are not implicated in cancer.

Cannabinoid-enriched e-liquids require sophisticated processing, and may lack information on quality control, expiry date, conditions of preservation, or toxicological/clinical assessment. It is assumed that vaporizing cannabinoids at lower temperatures is safer because it produces smaller amounts of toxicants than a traditional cigarette. As of 2015 the health effects specific cannabinoid vaping were unknown.{{cite journal |vauthors=Giroud C, de Cesare M, Berthet A, Varlet V, Concha-Lozano N, Favrat B |date=August 2015 |title=E-Cigarettes: A Review of New Trends in Cannabis Use |journal=International Journal of Environmental Research and Public Health |volume=12 |issue=8 |pages=9988–10008 |doi=10.3390/ijerph120809988 |pmc=4555324 |pmid=26308021 |doi-access=free}}{{CC-notice|cc=by4|url=http://www.mdpi.com/1660-4601/12/8/9988/htm|author(s)=Christian Giroud, Mariangela de Cesare, Aurélie Berthet, Vincent Varlet, Nicolas Concha-Lozano, and Bernard Favrat}} However, cannabinoid e-cigarettes mixed with other diluents and chemicals was associated with EVALI, although a 2017 study rejected this.{{Cite journal |last1=Boakye |first1=Ellen |last2=El Shahawy |first2=Omar |last3=Obisesan |first3=Olufunmilayo |last4=Dzaye |first4=Omar |last5=Osei |first5=Albert D. |last6=Erhabor |first6=John |last7=Uddin |first7=S. M. Iftekhar |last8=Blaha |first8=Michael J. |date=2022-10-17 |title=The inverse association of state cannabis vaping prevalence with the e-cigarette or vaping product-use associated lung injury |journal=PLOS ONE |volume=17 |issue=10 |pages=e0276187 |bibcode=2022PLoSO..1776187B |doi=10.1371/journal.pone.0276187 |issn=1932-6203 |pmc=9576092 |pmid=36251673 |doi-access=free}}

Various studies rate the public health impacts of vaping as far less negative than those of smoking.{{cite journal |vauthors=Franck C, Filion KB, Kimmelman J, Grad R, Eisenberg MJ |date=May 2016 |title=Ethical considerations of e-cigarette use for tobacco harm reduction |journal=Respiratory Research |volume=17 |issue=1 |page=53 |doi=10.1186/s12931-016-0370-3 |pmc=4869264 |pmid=27184265 |doi-access=free}}{{CC-notice|cc=by4|url=https://respiratory-research.biomedcentral.com/articles/10.1186/s12931-016-0370-3|author(s)=Caroline Franck, Kristian B. Filion, Jonathan Kimmelman, Roland Grad and Mark J. Eisenberg}}

E-cigarette emissions are not comparable to cigarette smoke as their chemical composition is completely different. Vapor content varies depending on the e-liquid, the device, and usage.{{cite web |date=April 2016 |title=Nicotine without smoke: Tobacco harm reduction |url=https://www.rcplondon.ac.uk/projects/outputs/nicotine-without-smoke-tobacco-harm-reduction-0 |publisher=Royal College of Physicians |pages=1–191 |vauthors=Wilder N, Daley C, Sugarman J, Partridge J |location=UK}} {{rp|84}} Exhaled vapor consists of mixtures of nicotine, ultrafine particles, primarily propylene glycol, glycerin, flavorings, and aroma transporters, aldehydes, and volatile organic chemicals (VOC) that form a visible fog. The vapor has a half-life of about 10 seconds; smoke lasts 100 times longer. A 2014 study reported that e-cigarettes increased levels of carcinogenic polycyclic aromatic hydrocarbons in the surrounding air.{{cite journal |vauthors=Nowak D, Jörres RA, Rüther T |date=May 2014 |title=E-cigarettes--prevention, pulmonary health, and addiction |journal=Deutsches Ärzteblatt International |volume=111 |issue=20 |pages=349–355 |doi=10.3238/arztebl.2014.0349 |pmc=4047602 |pmid=24882626}}

Vapor particles are larger than smoke particles, with a mean droplet size of 600 nm (inhaled) and 300 nm (exhaled) along with particles with a diameter of around 2.5 μm. Exhaled vapor concentration is 5 times lower than cigarette smoke. Particle density measured 6 to 880 times lower.

One 2015 study reported that exhaled vapor might have significant adverse effects. Another reported that e-cigarettes that do not contain nicotine may also generate hazardous vapors{{cite journal |vauthors=Neuberger M |date=May 2015 |title=The electronic cigarette: a wolf in sheep's clothing |journal=Wiener Klinische Wochenschrift |volume=127 |issue=9–10 |pages=385–387 |doi=10.1007/s00508-015-0753-3 |pmid=26230008 |s2cid=10172525}} and could present a second-hand risk.{{cite journal |vauthors=Hess IM, Lachireddy K, Capon A |date=April 2016 |title=A systematic review of the health risks from passive exposure to electronic cigarette vapour |journal=Public Health Research & Practice |volume=26 |issue=2 |doi=10.17061/phrp2621617 |pmid=27734060 |doi-access=free}} A third reported that vapor may include propylene glycol aerosols at levels that can cause eye and respiratory irritation and exceed California Environmental Protection Agency standards.{{cite web |year=2016 |title=E-Cigarette Use Among Youth and Young Adults: A Report of the Surgeon General |url=https://e-cigarettes.surgeongeneral.gov/documents/2016_SGR_Full_Report_non-508.pdf |publisher=Surgeon General of the United States |pages=1–298}}{{PD-notice}} A 2017 study reported that people living with e‐cigarette users had increased salivary nicotine concentrations. Another reported that some non-users reported adverse effects from second-hand vapor.

A 2016 survey reported that nearly half of middle and high school students had been exposed.

As of 2014 neither the long-term nor short-term{{cite journal |vauthors=Fernández E, Ballbè M, Sureda X, Fu M, Saltó E, Martínez-Sánchez JM |date=December 2015 |title=Particulate Matter from Electronic Cigarettes and Conventional Cigarettes: a Systematic Review and Observational Study |journal=Current Environmental Health Reports |volume=2 |issue=4 |pages=423–429 |bibcode=2015CEHR....2..423F |doi=10.1007/s40572-015-0072-x |pmid=26452675 |doi-access=free}}{{cite web |date=25 August 2014 |title=American Lung Association Statement on E-Cigarettes |url=http://www.lung.org/stop-smoking/tobacco-control-advocacy/federal/e-cigarettes.html |publisher=American Lung Association}} health effects from exhaled vapor were known. A 2017 review concluded that the few studies that examined the effect of indoor air quality on human test subjects in natural settings produced inconsistent results. As of 2018 limited only information of the effects of exhaled vapor on children was available.{{cite journal |vauthors=Collaco JM, McGrath-Morrow SA |date=April 2018 |title=Electronic Cigarettes: Exposure and Use Among Pediatric Populations |journal=Journal of Aerosol Medicine and Pulmonary Drug Delivery |volume=31 |issue=2 |pages=71–77 |doi=10.1089/jamp.2017.1418 |pmc=5915214 |pmid=29068754}}

File:Smoking-smoke-cigarette-man-lung-cancer-1.jpg (vapor) exhaled by an vaper may expose non-users to second-hand vapor.{{cite web |date=8 December 2016 |title=Surgeon General Reports Youth and Young Adult E-Cigarette Use Poses a Public Health Threat |url=https://www.hhs.gov/about/news/2016/12/08/surgeon-general-reports-youth-and-young-adult-e-cigarette-use-poses-public-health-threat.html |archive-url=https://wayback.archive-it.org/3926/20170128144427/https://www.hhs.gov/about/news/2016/12/08/surgeon-general-reports-youth-and-young-adult-e-cigarette-use-poses-public-health-threat.html |archive-date=28 January 2017 |access-date=13 March 2021 |publisher=United States Department of Health and Human Services}}{{PD-notice}}]]

Between January 2012 and December 2014, FDA published 35 adverse effect reports regarding second-hand vapor exposure.{{cite journal |vauthors=Glasser AM, Collins L, Pearson JL, Abudayyeh H, Niaura RS, Abrams DB, Villanti AC |date=February 2017 |title=Overview of Electronic Nicotine Delivery Systems: A Systematic Review |journal=American Journal of Preventive Medicine |volume=52 |issue=2 |pages=e33–e66 |doi=10.1016/j.amepre.2016.10.036 |pmc=5253272 |pmid=27914771}}

A 2018 study reported PM_2.5 levels in a large hotel event room (4,023m³) increased from 2–3 μg/m³ to as high as 819 μg/m³ (interquartile range: 761–975 μg/m³) when 59–86 people were vaping. This level exceeded the US Environmental Protection Agency annual time-weighted standard for PM_2.5 of 12 μg/m³.

A 2018 review concluded that bystanders absorb nicotine when people around them use e-cigarettes at levels comparable with exposure to second-hand smoke. It included a study comparing non-smokers living with vapers, with smokers, and non-users (controls). That study found cotinine (a nicotine metabolite) levels in urine were significantly elevated in the first two groups vs the controls, but were not significantly different, despite the fact that air pollution levels in the smokers' homes was much higher than in the vapers' homes (geometric mean air nicotine concentrations of 0.13 μg/m³ in vapers' homes, 0.74 μg/m³ in smokers' homes, and 0.02 μg/m³ in the control homes). A 2014 practice guideline by NPS MedicineWise stated that serum cotinine levels were similar in bystanders exposed to either vapour or smoke.{{cite web |date=11 June 2014 |title=e-Cigarettes: a safe way to quit? |url=http://www.nps.org.au/publications/health-professional/health-news-evidence/2014/e-cigarettes |archive-url=https://web.archive.org/web/20170319045556/http://www.nps.org.au/publications/health-professional/health-news-evidence/2014/e-cigarettes |archive-date=19 March 2017 |publisher=NPS MedicineWise}}

In 2014, several groups came out against e-cigarettes. The International Union Against Tuberculosis and Lung Disease stated, "Adverse health effects for exposed third parties (second-hand exposure) cannot be excluded because the use of e-cigarettes leads to emission of fine and ultrafine inhalable liquid particles, nicotine and cancer-causing substances into indoor air."{{cite journal |vauthors=Bam TS, Bellew W, Berezhnova I, Jackson-Morris A, Jones A, Latif E, Molinari MA, Quan G, Singh RJ, Wisotzky M |date=January 2014 |title=Position statement on electronic cigarettes or electronic nicotine delivery systems |journal=The International Journal of Tuberculosis and Lung Disease |volume=18 |issue=1 |pages=5–7 |doi=10.5588/ijtld.13.0815 |pmid=24365545 |s2cid=26481455}} The American Industrial Hygiene Association concluded that "e-cigarettes are not emission-free and that their pollutants could be of health concern for users and those who are exposed secondhand....[T]heir use in the indoor environment should be restricted, consistent with current smoking bans, until and unless research documents that they will not significantly increase the risk of adverse health effects to room occupants."{{cite web |date=19 October 2014 |title=White Paper: Electronic Cigarettes in the Indoor Environment |url=http://tobacco.ucsf.edu/sites/tobacco.ucsf.edu/files/u9/AIHA-Electronc%20Cig%20Document_Final.pdf |archive-url=https://web.archive.org/web/20170125045708/http://tobacco.ucsf.edu/sites/tobacco.ucsf.edu/files/u9/AIHA-Electronc%20Cig%20Document_Final.pdf |archive-date=25 January 2017 |access-date=18 August 2016 |publisher=American Industrial Hygiene Association}} Similarly, in 2016 the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) updated its standard for "Ventilation for Acceptable Indoor Air Quality" to incorporate emissions from e-cigarettes into the definition of "environmental tobacco smoke," which is incompatible with acceptable indoor air quality. A 2017 French "experts statement" recommended banning vaping indoors in public and working areas.{{cite journal |vauthors=Dautzenberg B, Adler M, Garelik D, Loubrieu JF, Mathern G, Peiffer G, Perriot J, Rouquet RM, Schmitt A, Underner M, Urban T |date=February 2017 |title=Practical guidelines on e-cigarettes for practitioners and others health professionals. A French 2016 expert's statement |journal=Revue des Maladies Respiratoires |volume=34 |issue=2 |pages=155–164 |doi=10.1016/j.rmr.2017.01.001 |pmid=28189437}}

A 2014 WHO report stated passive exposure was a concern, indicating that current evidence is insufficient to determine whether the levels of exhaled vapor are safe to involuntarily exposed bystanders. The report stated that "it is unknown if the increased exposure to toxicants and particles in exhaled aerosol will lead to an increased risk of disease and death among bystanders." A 2016 WHO report stated, "While some argue that exposure to SHA [second-hand aerosol] is unlikely to cause significant health risks, they concede that SHA can be deleterious to bystanders with some respiratory pre-conditions. It is nevertheless reasonable to assume that the increased concentration of toxicants from SHA over background [air] levels poses an increased risk for the health of all bystanders."{{cite web |date=August 2016 |title=Electronic Nicotine Delivery Systems and Electronic Non-Nicotine Delivery Systems (ENDS/ENNDS) |url=https://www.who.int/fctc/cop/cop7/FCTC_COP_7_11_EN.pdf |publisher=World Health Organization WHO |pages=1–11}}{{rp|4}}

Several medical organizations advocate that vaping be banned in public places and workplaces.{{cite journal |vauthors=Kaur J, Rinkoo AV |date=September 2017 |title=Getting real with the upcoming challenge of electronic nicotine delivery systems: The way forward for the South-East Asia region |journal=Indian Journal of Public Health |volume=61 |issue=Suppl 1 |pages=S7–S11 |doi=10.4103/ijph.IJPH_240_17 |pmid=28928312 |doi-access=free}} A 2014 review concluded it is safe to infer that their effects on bystanders are minimal in comparison to traditional cigarettes. E-cigarette vapor has notably fewer toxicants than cigarette smoke.

File:No_Vaping_Sign_(18562436519).jpg

A 2015 California Department of Public Health report stated that vapour "has been reported to contain at least ten chemicals that are on California's Proposition 65 list of chemicals known to cause cancer, birth defects, or other reproductive harm."{{cite web |date=January 2015 |title=State Health Officer's Report on E-Cigarettes: A Community Health Threat |url=https://www.cdph.ca.gov/Programs/CCDPHP/DCDIC/CTCB/CDPH%20Document%20Library/Policy/ElectronicSmokingDevices/StateHealthEcigReport.pdf |publisher=California Tobacco Control Program (California Department of Public Health) |pages=1–21}}{{PD-notice}}{{rp|1}}

A 2017 study reported that some chemicals could violate workplace safety standards.{{cite journal |vauthors=Clapp PW, Jaspers I |date=October 2017 |title=Electronic Cigarettes: Their Constituents and Potential Links to Asthma |journal=Current Allergy and Asthma Reports |volume=17 |issue=11 |page=79 |doi=10.1007/s11882-017-0747-5 |pmc=5995565 |pmid=28983782}} A review of convention studies concluded that second-hand vapor may be significant, particularly for workers who repeatedly encounter it. Exposure studies suggest that indoor vaping is higher than the smoke-free level put forth by the US Surgeon General and the WHO Framework Convention on Tobacco Control.{{rp|Secondhand Exposure to E-Cigarette Aerosol, Synthesis; 84}}

A 2014 review suggested that vapor contaminant levels do not exceed workplace safety standards,{{cite journal |vauthors=Burstyn I |date=January 2014 |title=Peering through the mist: systematic review of what the chemistry of contaminants in electronic cigarettes tells us about health risks |journal=BMC Public Health |volume=14 |issue=1 |page=18 |doi=10.1186/1471-2458-14-18 |pmc=3937158 |pmid=24406205 |doi-access=free}} and are mostly below 1% of permissible levels. However, workplace standards do not consider more vulnerable groups such as those in poor health, children, and infants. 2 015 PHE report concluded that e-cigarettes "release negligible levels of nicotine into ambient air with no identified health risks to bystanders".{{rp|65}}

Direct exposure happens via e-liquid inhalation, ingestion, skin contact, or vapor residue accumulation on surfaces. Direct exposure is almost always inadvertent, and results from improper product use. Exposure can involve much higher concentrations than exhaled vapor.

Exposure may involve a leaking or spilled e-liquid cartridge or bottle.

E-liquid quickly absorbs into the skin{{cite journal |vauthors=Meo SA, Al Asiri SA |year=2014 |title=Effects of electronic cigarette smoking on human health |url=http://www.europeanreview.org/wp/wp-content/uploads/3315-3319.pdf |journal=European Review for Medical and Pharmacological Sciences |volume=18 |issue=21 |pages=3315–3319 |pmid=25487945}} and local irritation can follow.{{cite journal |vauthors=Biyani S, Derkay CS |date=March 2017 |title=E-cigarettes: An update on considerations for the otolaryngologist |journal=International Journal of Pediatric Otorhinolaryngology |volume=94 |pages=14–16 |doi=10.1016/j.ijporl.2016.12.027 |pmid=28167004}} Less than 1 tablespoon can cause adverse effects such as seizures, anoxic brain trauma, vomiting, lactic acidosis,{{rp|Summary, Conclusion 14-2.; 9}} cardiac arrest, seizures, or coma.{{cite journal |vauthors=Frey LT, Tilburg WC |date=February 2016 |title=Child-Resistant Packaging for E-Liquid: A Review of US State Legislation |journal=American Journal of Public Health |volume=106 |issue=2 |pages=266–268 |doi=10.2105/AJPH.2015.302957 |pmc=4815607 |pmid=26691114}} A potentially fatal dose for a child is 0.1–0.2 mg/kg of body weight, or 6 mg.{{cite journal |vauthors=Jimenez Ruiz CA, Solano Reina S, de Granda Orive JI, Signes-Costa Minaya J, de Higes Martinez E, Riesco Miranda JA, Altet Gómez N, Lorza Blasco JJ, Barrueco Ferrero M, de Lucas Ramos P |date=August 2014 |title=The electronic cigarette. Official statement of the Spanish Society of Pneumology and Thoracic Surgery (SEPAR) on the efficacy, safety and regulation of electronic cigarettes |journal=Archivos de Bronconeumologia |volume=50 |issue=8 |pages=362–367 |doi=10.1016/j.arbres.2014.02.006 |pmid=24684764}} A fatal dose for an adult is 0.5–1 mg/kg or about 30–60 mg.{{cite journal |vauthors=Dagaonkar RS, Udwadi ZF |date=April 2014 |title=Water pipes and E-cigarettes: new faces of an ancient enemy |url=http://www.japi.org/april_2014/05_ra_water_pipes.pdf |journal=The Journal of the Association of Physicians of India |volume=62 |issue=4 |pages=324–328 |pmid=25327035 |archive-url=https://web.archive.org/web/20160304031321/http://www.japi.org/april_2014/05_ra_water_pipes.pdf |archive-date=2016-03-04 |access-date=2015-02-25}} However the widely used human LD₅₀ estimate of around 0.8 mg/kg was questioned in a 2013 review, in light of documented cases of humans surviving much higher doses; the lower fatal limit was 500–1000 mg of ingested nicotine, which is equivalent to 6.5–13 mg/kg orally.{{cite journal |vauthors=Mayer B |date=January 2014 |title=How much nicotine kills a human? Tracing back the generally accepted lethal dose to dubious self-experiments in the nineteenth century |journal=Archives of Toxicology |volume=88 |issue=1 |pages=5–7 |bibcode=2014ArTox..88....5M |doi=10.1007/s00204-013-1127-0 |pmc=3880486 |pmid=24091634}}

E‐cigarettes can be unsafe to non-users via third-hand exposure, including children, pregnant women, nursing mothers, casino employees, housekeeping employees, and vulnerable groups.

In one scenario, indoor surfaces can accumulate nicotine-laden vapor residue.{{cite journal |vauthors=England LJ, Bunnell RE, Pechacek TF, Tong VT, McAfee TA |date=August 2015 |title=Nicotine and the Developing Human: A Neglected Element in the Electronic Cigarette Debate |journal=American Journal of Preventive Medicine |volume=49 |issue=2 |pages=286–293 |doi=10.1016/j.amepre.2015.01.015 |pmc=4594223 |pmid=25794473}} However, the extent of such contamination has not been established. A 2015 PHE report stated that an infant would have to lick 30 square meters to be exposed to 1 mg of nicotine.{{rp|65}} As with any potential hazard, childhood exploratory behavior creates risks not faced by others.{{cite journal |vauthors=Brown CJ, Cheng JM |date=May 2014 |title=Electronic cigarettes: product characterisation and design considerations |journal=Tobacco Control |volume=23 |issue=Supplement 2 |pages=ii4–i10 |doi=10.1136/tobaccocontrol-2013-051476 |pmc=3995271 |pmid=24732162}}

Children are more likely to mistake a colorful e-liquid container for a juice container.{{cite journal |vauthors=Pepper JK, Brewer NT |date=September 2014 |title=Electronic nicotine delivery system (electronic cigarette) awareness, use, reactions and beliefs: a systematic review |journal=Tobacco Control |volume=23 |issue=5 |pages=375–384 |doi=10.1136/tobaccocontrol-2013-051122 |pmc=4520227 |pmid=24259045}}{{cite journal |vauthors=Modesto-Lowe V, Alvarado C |date=September 2017 |title=E-cigs . . . Are They Cool? Talking to Teens About E-Cigarettes |journal=Clinical Pediatrics |volume=56 |issue=10 |pages=947–952 |doi=10.1177/0009922817705188 |pmid=28443340 |s2cid=44423931}}{{cite web |date=2 May 2018 |title=Do You Vape? See These Tips on How to Keep E-Liquids Away from Children |url=https://www.fda.gov/ForConsumers/ConsumerUpdates/ucm606055.htm |archive-url=https://web.archive.org/web/20180501224809/https://www.fda.gov/ForConsumers/ConsumerUpdates/ucm606055.htm |url-status=dead |archive-date=1 May 2018 |publisher=United States Food and Drug Administration}}{{PD-notice}} The US mandates child-proof packaging.{{cite news |date=9 May 2016 |title=E-Cigarette Poisonings Among Toddlers Skyrocketed 1500% Over 3 Years |url=https://www.yahoo.com/news/e-cigarette-poisonings-among-toddlers-134400321.html |work=Yahoo! News}}

As of 2019 a few incidents of intentional self-harm by ingesting or injecting e-liquids had been reported.{{cite journal |vauthors=Bhatnagar A, Whitsel LP, Ribisl KM, Bullen C, Chaloupka F, Piano MR, Robertson RM, McAuley T, Goff D, Benowitz N |date=October 2014 |title=Electronic cigarettes: a policy statement from the American Heart Association |journal=Circulation |volume=130 |issue=16 |pages=1418–1436 |doi=10.1161/CIR.0000000000000107 |pmc=7643636 |pmid=25156991 |doi-access=free}} Death from intentional nicotine poisoning is almost unknown.{{rp|63}}

In 2017, FDA stated that e-cigarette aerosols can cause problems for both users and their pets. Some studies reported that aerosols may provide exposure to higher-than-normal amounts of nicotine and other toxic chemicals, such as formaldehyde. E-cigarettes typically use capsules to contain nicotine.{{cite web |date=19 October 2017 |title=Be Smoke-free and Help Your Pets Live Longer, Healthier Lives - Electronic Nicotine Delivery Systems |url=https://www.fda.gov/animal-veterinary/animal-health-literacy/be-smoke-free-and-help-your-pets-live-longer-healthier-lives#systems |publisher=United States Food and Drug Administration}}{{PD-notice}} Pets may find and bite them or expose themselves to the liquid refilling solution. In a 15 March 2016, letter to the editor of the Journal of the American Veterinary Medical Association, the Texas Poison Center Networkhttps://www.poisoncontrol.org/home/ Texas Poison Control Network reported 11 cases of dog exposures to e-cigarettes or refills. The Animal Poison Control Center stated that among nicotine toxicity cases in 2012, 4.6% related to e-cigarettes, which increased to 13.6% in 2013.{{cite web |date=2019 |title=E-cigarettes and Pet Safety |url=http://vcahospitals.com/know-your-pet/e-cigarettes-and-pet-safety |publisher=VCA Corporate}}

The long-term health impacts of vaping are unknown, particularly given the variety of EC devices, e‑liquids, and consumption patterns. This specifically applies to nicotine and propylene glycol.{{cite web |date=May 2014 |title=Cancer Research UK Briefing: Electronic Cigarettes |url=http://www.cancerresearchuk.org/sites/default/files/policy_may2014_e-cigarette_briefing.pdf |publisher=Cancer Research UK}} Limited peer-reviewed data restricts the scope of toxicological evaluation;{{cite journal |vauthors=Orr MS |date=May 2014 |title=Electronic cigarettes in the USA: a summary of available toxicology data and suggestions for the future |journal=Tobacco Control |volume=23 |issue=Supplement 2 |pages=ii18–ii22 |doi=10.1136/tobaccocontrol-2013-051474 |pmc=3995288 |pmid=24732158}} their cytotoxicity is unknown.{{cite journal |vauthors=Rahman MA, Hann N, Wilson A, Worrall-Carter L |year=2014 |title=Electronic cigarettes: patterns of use, health effects, use in smoking cessation and regulatory issues |journal=Tobacco Induced Diseases |volume=12 |issue=1 |page=21 |doi=10.1186/1617-9625-12-21 |pmc=4350653 |pmid=25745382 |doi-access=free}} A 2014 review concluded that few e-cigarettes had undergone a thorough toxicology evaluation and testing.{{cite journal |vauthors=Xu Y, Guo Y, Liu K, Liu Z, Wang X |year=2016 |title=E-Cigarette Awareness, Use, and Harm Perception among Adults: A Meta-Analysis of Observational Studies |journal=PLOS ONE |volume=11 |issue=11 |pages=e0165938 |bibcode=2016PLoSO..1165938X |doi=10.1371/journal.pone.0165938 |pmc=5115669 |pmid=27861501 |doi-access=free}} A 2013 study claimed that they were similar in toxicity to other nicotine replacement products,{{cite journal |vauthors=Caponnetto P, Russo C, Bruno CM, Alamo A, Amaradio MD, Polosa R |date=March 2013 |title=Electronic cigarette: a possible substitute for cigarette dependence |journal=Monaldi Archives for Chest Disease = Archivio Monaldi per le Malattie del Torace |volume=79 |issue=1 |pages=12–19 |doi=10.4081/monaldi.2013.104 |pmid=23741941 |doi-access=free}} but this was disputed.{{rp|87}} In 2013 the UK National Health Service noted that toxic chemical levels were 0.1% of cigarette smoke.{{cite web |date=12 June 2013 |title=E-cigarettes to be regulated as medicines |url=http://www.nhs.uk/news/2013/06June/Pages/e-cigarettes-and-vaping.aspx |archive-url=https://web.archive.org/web/20151217052020/http://www.nhs.uk/news/2013/06June/Pages/e-cigarettes-and-vaping.aspx |archive-date=17 December 2015 |access-date=21 November 2014 |publisher=National Health Service}}

E-cigarettes supply nicotine and other toxins at rates far below traditional cigarettes and other nicotine delivery systems:{{cite journal |vauthors=Cooke A, Fergeson J, Bulkhi A, Casale TB |year=2015 |title=The Electronic Cigarette: The Good, the Bad, and the Ugly |journal=The Journal of Allergy and Clinical Immunology. In Practice |volume=3 |issue=4 |pages=498–505 |doi=10.1016/j.jaip.2015.05.022 |pmid=26164573}}

{{close paraphrasing |section|source=http://journal.frontiersin.org/article/10.3389/fonc.2015.00196/full|free=yes|talk=notvio|date=May 2025}}

Concerns about carcinogenicity arise from both nicotine{{cite journal |vauthors=Jerry JM, Collins GB, Streem D |date=August 2015 |title=E-cigarettes: Safe to recommend to patients? |journal=Cleveland Clinic Journal of Medicine |volume=82 |issue=8 |pages=521–526 |doi=10.3949/ccjm.82a.14054 |pmid=26270431 |doi-access=free}} and from other vapor chemicals.

Evidence from in vitro and animal research does not indicate carcinogenicity in vivo. A 2014 Surgeon General report stated that the only relevant randomized trial "does not indicate a strong role for nicotine in promoting carcinogenesis in humans". It concluded that data is insufficient "to conclude that nicotine causes or contributes to cancer in humans, but there is evidence showing possible oral, esophageal, or pancreatic cancer risks".{{cite book |author1=National Center for Chronic Disease Prevention Health Promotion (US) Office on Smoking Health |url=https://stacks.cdc.gov/view/cdc/21569/Share |title=The Health Consequences of Smoking—50 Years of Progress: A Report of the Surgeon General |publisher=Surgeon General of the United States |year=2014 |pages=1–943 |pmid=24455788}} {{rp|116}} However, a 2014 study suggested that vaping may be a risk factor for lung cancer. Nicotine in the form of nicotine replacement products is reported to be less of a cancer risk than smoking,{{rp|115}} and they vaping had not been shown to be associated with cancer.

As of 2015 it was not possible to conclude that nicotine itself is a complete carcinogen. In mice studies with NNK as an initiator, nicotine was reported to act as a promoter after injection or dermal absorption, but not after oral administration. In drinking water experiments, considerable first-pass metabolism of nicotine occurred before nicotine entered systemic circulation. As a result, serum concentration is much lower after ingestion than after intraperitoneal injection administration.{{cite journal |vauthors=Sanner T, Grimsrud TK |year=2015 |title=Nicotine: Carcinogenicity and Effects on Response to Cancer Treatment - A Review |journal=Frontiers in Oncology |volume=5 |page=196 |doi=10.3389/fonc.2015.00196 |pmc=4553893 |pmid=26380225 |doi-access=free}}{{CC-notice|cc=by4|url=http://journal.frontiersin.org/article/10.3389/fonc.2015.00196/full|vauthors=Sanner T, Grimsrud TK}}

However, nicotine has been reported to promote metastasis by causing cell cycle progression, epithelial-to-mesenchymal transition, migration, invasion, angiogenesis, and avoidance of apoptosis.{{cite journal |vauthors=Schaal C, Chellappan SP |date=January 2014 |title=Nicotine-mediated cell proliferation and tumor progression in smoking-related cancers |journal=Molecular Cancer Research |volume=12 |issue=1 |pages=14–23 |doi=10.1158/1541-7786.MCR-13-0541 |pmc=3915512 |pmid=24398389}} Nicotine promotes the growth of blood vessels, which can supply tumors and speed tumor growth. As of 2015, long-term vaping had not been assessed for malignancy in individuals with a susceptibility for tumor growth. The effects of nicotine on the sympathoadrenal system could stimulate growth in cancers already present.{{cite journal |vauthors=Mravec B, Tibensky M, Horvathova L, Babal P |date=February 2020 |title=E-Cigarettes and Cancer Risk |journal=Cancer Prevention Research |volume=13 |issue=2 |pages=137–144 |doi=10.1158/1940-6207.CAPR-19-0346 |pmid=31619443 |doi-access=free}}

Multiple in vitro experiments reported that nicotine in concentrations as low as 1 μM decreased the anti-proliferative and pro-apoptotic effects exerted by chemotherapeutics on multiple malignant cell lines. These effects were partially reverted by exposure to α-bungarotoxin (α-BTX), a α7-nAChR inhibitor. During radiotherapy (RT), nicotine administration was reported to increase survival of H460 and A549 lung cancer cells. This effect was likewise reduced by addition of α-BTX prior to nicotine addition and radiation. On this basis, it may be expected that use of nicotine products during cancer treatment reduces the effects due to reactions following interaction of nicotine with α7-nAChR.

File:Endogenous_Formation_of_Tobacco-specific_N-nitrosamines_(TSNA).jpg (TSNAs) may occur after absorption of nicotine.]]

Evidence from in vitro studies on cell cultures, rodents and humans inclusive of epidemiological studies indicate that nicotine may contribute in cancer development by stimulating important processes. Nicotine acts primarily by activation of nicotine acetylcholine receptors (NAR) and nicotine binds to these receptors with a higher affinity than acetylcholine. Furthermore, the tobacco-specific nitrosamines (TSNAs) NNN (N′-nitrosonornicotine) and the potent lung carcinogen NNK (4-(metylnitrosamino)-1-(3-pyridyl)-1-butanon) may be formed from nicotine after oral administration. E-cigarettes deliver NNK. Some evidence indicates that the NNK dose-response curve for cancer is highly nonlinear, with substantial risk at low doses.

A 2015 study reported that urine from vapers had low levels of NNAL (4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol), which may suggest that endogenous formation of TSNA after nicotine inhalation is negligible. That data indicates that TSNA may be formed internally after absorption of nicotine through the oral mucous membranes and through the skin, while formation after lung absorption may be negligible. Thus, the toxicokinetics of nicotine may depend on the administration route.

The interaction of nicotine with NARs activates signaling pathways that trigger multiple reactions, such as increased cell proliferation and cell survival. Although NARs are the primary receptors, nicotine binding to β-ARs and EGFRs may also be important. Nicotine induces epithelial–mesenchymal transition, which is one of the vital steps for the acquisition of malignant phenotype. This transition allows the cell to acquire migratory properties, which may facilitate cancer metastases.

In May 2014, Cancer Research UK stated that very preliminary unpublished results "suggest that e-cigarettes promote tumour growth in human cells."

Nicotine enhanced tumor growth and progression after injection of malignant cells in mice. Enhancements were reported both after exposure by intraperitoneal injection, oral, and skin administration. Moreover, cotinine did also enhance tumor growth. Nicotine may inhibit antitumor immune response. It has been reported that exposure to nicotine adversely affects dendritic cells, a cell type that has an important role in anticancer immunosurveillance. Moreover, in studies on xenograft in mice, nicotine was reported to reduce the effects of radiotherapy and chemoradiotherapy.

No long-term research considers the cancer risk related to the relatively small level of exposure to the identified carcinogens in e-cigarette vapor. Their long-term use is anticipated to raise the risk of developing lung cancer.{{rp|3}} A 2015 study reported carcinogenicity was mainly evident in the lungs, mouth, and throat, which may be associated with nitrosamines, propylene glycol, and some flavoring additives. A 2019 review associated vaping with a possible risk of head and neck cancers.{{cite journal |vauthors=Flach S, Maniam P, Manickavasagam J |date=September 2019 |title=E-cigarettes and head and neck cancers: A systematic review of the current literature |url=https://discovery.dundee.ac.uk/en/publications/18d4c6c7-6579-4b70-9088-dde6b6e21421 |journal=Clinical Otolaryngology |volume=44 |issue=5 |pages=749–756 |doi=10.1111/coa.13384 |pmid=31148389 |s2cid=171094189}}

Since e-liquids are made from tobacco they may contain impurities such cotinine, anabasine, anatabine, myosmine and beta-nicotyrine. The health implications of suchimpurities are not known. A 2016 review concluded, "impurities and nicotine degradation products such as nicotine-cis-N-oxide, nicotine-trans-N-oxide, myosmine, anabasine, and anatabine, which are very carcinogenic, can be reported in e-cigarette refill liquids. The molecules can lead to mutations in genes such as Ras (vital function in signal transduction of cell proliferation), p53 and retinoblastoma (with roles as tumour suppressors) as these molecules can form adducts with cellular DNA." The majority of e-cigarettes evaluated included carcinogenic TSNAs; heavy metals such as cadmium, nickel, and lead; and the carcinogen toluene. However, in comparison to traditional cigarette smoke, the toxic substance levels identified in e-cigarette vapor were 9- to 450-fold less.

Nicotine promotes endothelial cell migration, proliferation, survival, tube formation, and nitric oxide (NO) production in vitro, mimicking the effect of other angiogenic growth factors. In 2001, it was reported that nicotine was a potent angiogenic agent at tissue and plasma concentrations similar to those induced by light to moderate smoking. Angiogenic effects on tumor cells were found in breast, colon, and lung cancers. Similar results were demonstrated in in vivo mouse models of lung cancer, where nicotine significantly increased tumor size and numbers in the lung, and enhanced metastasis. At high enough concentration levels, nicotine becomes cytotoxic.

Nicotine has been reported to damage DNA, assessed by the Escherichia colipol A+/pol− test. A 2015 review concluded that nicotine decreases Chk2, a tumor suppressor, which is otherwise activated by DNA damage. The Chk2 decrease suggests nicotine may be able to override DNA damage checkpoint activation, disrupt genetic surveillance, and increase the risk of oncogenesis. One 2018 study reported strong evidence that some vapor substances such as formaldehyde and acrolein can induce DNA damage and mutagenesis.{{rp|Summary, Conclusion 10–4.; 8}}

Nicotine can induce chromosomal aberration, chromatid exchange, single-strand DNA strand breaks, and micronuclei in vitro. Oxidative stress is likely involved, since the effects are reduced when antioxidants are present. The effects decrease after co-incubation with a NAR antagonist, indicating a receptor-dependent pathway for oxidative stress induction.

Vapor triggered DNA strand breaks and lowered cell survival in vitro, regardless of nicotine content. A 2013 study reported that some vapor samples had cytotoxic effects on cardiac muscle cells, (albeit less than those of cigarette smoke).{{cite journal |vauthors=Knorst MM, Benedetto IG, Hoffmeister MC, Gazzana MB |date=October 2014 |title=The electronic cigarette: the new cigarette of the 21st century? |journal=Jornal Brasileiro de Pneumologia |volume=40 |issue=5 |pages=564–572 |doi=10.1590/S1806-37132014000500013 |pmc=4263338 |pmid=25410845}} A 2016 review concluded that vapor had adverse effects on primary airway epithelial cells and tumor cell lines, and other epithelial cell lines, that ranged from reducing viability, increase in production of inflammatory mediators and oxidative stress, reduced antimicrobial defences and increased pro-carcinogenic events.{{cite journal |vauthors=Hiemstra PS, Bals R |date=October 2016 |title=Basic science of electronic cigarettes: assessment in cell culture and in vivo models |journal=Respiratory Research |volume=17 |issue=1 |page=127 |doi=10.1186/s12931-016-0447-z |pmc=5055681 |pmid=27717371 |doi-access=free}}{{CC-notice|cc=by4|url=https://respiratory-research.biomedcentral.com/articles/10.1186/s12931-016-0447-z|vauthors=Hiemstra PS, Bals R}}

File:Toxicants_emitted_by_tobacco_cigarettes_and_e-cigarettes_ehp.122-A244.t001.png

File:Propylene_glycol_chemical_structure.png molecule]]

The primary base ingredients of e-liquids are propylene glycol and glycerin. About 20% to 27% of propylene glycol and glycerin-based liquid particles are inhaled.{{cite journal |vauthors=Alawsi F, Nour R, Prabhu S |date=August 2015 |title=Are e-cigarettes a gateway to smoking or a pathway to quitting? |journal=British Dental Journal |volume=219 |issue=3 |pages=111–115 |doi=10.1038/sj.bdj.2015.591 |pmid=26271862 |s2cid=24120636}} A 2016 study reported that 6% of nicotine, 8% of propylene glycol, and 16% of glycerin was exhaled.{{rp|162}} As of 2014 the long-term effects of inhaled propylene glycol and glycerin were unknown. Exposure to propylene glycol may cause eye and respiratory tract irritation. Heated and aerosolized propylene glycol can turn into propylene oxide, which the International Agency for Research on Cancer (IARC) labels a possible human carcinogen. A 2014 review concluded that the risk from propylene glycol and glycerin inhalation is probably low, although they have not been demonstrated to be safe. A 2013 German Cancer Center report stated that long-term indoor inhalation of propylene glycol could increase childhood asthma risks. As of 2014, some companies replaced propylene glycol with water and glycerin. A 2019 study reported that inhaled glycerin could cause lipoid pneumonia.{{cite journal |vauthors=Papaefstathiou E, Stylianou M, Agapiou A |date=May 2019 |title=Main and side stream effects of electronic cigarettes |journal=Journal of Environmental Management |volume=238 |pages=10–17 |bibcode=2019JEnvM.238...10P |doi=10.1016/j.jenvman.2019.01.030 |pmid=30836280 |s2cid=73462201}} A 2017 review concluded that propylene glycol and glycerin increased the amount of hydrogen peroxide.{{Clarify|Where was the hp found?|date=January 2025}}

Some e-liquids produced acrolein in the aerosol (a probable carcinogen),{{Cite web|url=https://www.cancer.org/cancer/risk-prevention/understanding-cancer-risk/known-and-probable-human-carcinogens.html|title=Known and Probable Human Carcinogens|website=www.cancer.org}} possibly from heated glycerin. A 2014 review concluded that acrolein levels were reduced by 60% in dual users and 80% for those that completely switched to e-cigarettes when compared to traditional cigarettes. Another 2014 review concluded that acrolein may induce irritation to the upper respiratory tract, while a 2014 study reported harm to the lining of the lungs.{{cite journal |vauthors=Bekki K, Uchiyama S, Ohta K, Inaba Y, Nakagome H, Kunugita N |date=October 2014 |title=Carbonyl compounds generated from electronic cigarettes |journal=International Journal of Environmental Research and Public Health |volume=11 |issue=11 |pages=11192–11200 |doi=10.3390/ijerph111111192 |pmc=4245608 |pmid=25353061 |doi-access=free}} A 2017 review concluded that acrolein induces oxidative stress and inflammation, disrupting lung endothelial cell barrier function and may lead to chronic obstructive pulmonary disease. Another 2017 review stated, "based on the average of 120 puffs/day reported in the literature, our calculated levels of acrolein emitted by e‐cigarette users per day were reported to vary between 0.00792 and 8.94 ppm/day."

A 2015 study reported that vapor created oxidants and reactive oxygen species (OX/ROS). OX/ROS could react with other vaporized substances because they are highly reactive. E-cigarettes were reported to contain OX/ROS at about 100 times less than in cigarette smoke. A 2014 study reported that e-liquids from a specific manufacturer contained greater amounts of ethylene glycol than glycerin or propylene glycol, although ethylene glycol was not permitted for use in products meant for human consumption.{{cite journal |vauthors=Dinakar C, O'Connor GT |date=October 2016 |title=The Health Effects of Electronic Cigarettes |journal=The New England Journal of Medicine |volume=375 |issue=14 |pages=1372–1381 |doi=10.1056/NEJMra1502466 |pmid=27705269}}

File:Blu_Cigs_Cartridges_(9832539844)_crop.jpg

Flavored e-liquids contain additional substances in part to disguise nicotine's bitter taste. Their health effects are not entirely known,{{cite journal |author-link4=Najat A. Saliba |vauthors=Schick SF, Blount BC, Jacob P, Saliba NA, Bernert JT, El Hellani A, Jatlow P, Pappas RS, Wang L, Foulds J, Ghosh A, Hecht SS, Gomez JC, Martin JR, Mesaros C, Srivastava S, St Helen G, Tarran R, Lorkiewicz PK, Blair IA, Kimmel HL, Doerschuk CM, Benowitz NL, Bhatnagar A |date=September 2017 |title=Biomarkers of exposure to new and emerging tobacco delivery products |journal=American Journal of Physiology. Lung Cellular and Molecular Physiology |volume=313 |issue=3 |pages=L425–L452 |doi=10.1152/ajplung.00343.2016 |pmc=5626373 |pmid=28522563}} given limited toxicological data. A 2017 study reported that flavorings can be a significant part of toxicants.{{cite journal |vauthors=Ramôa CP, Eissenberg T, Sahingur SE |date=October 2017 |title=Increasing popularity of waterpipe tobacco smoking and electronic cigarette use: Implications for oral healthcare |journal=Journal of Periodontal Research |volume=52 |issue=5 |pages=813–823 |doi=10.1111/jre.12458 |pmc=5585021 |pmid=28393367}} Each flavoring has a different chemical composition. A 2015 study reported varied cytotoxicity of e-liquids, ranging from little to significant cytotoxicity. The liquids contain aromatic substances such as tobacco, fruit, vanilla, caramel, and coffee. Typically, these additives are imprecisely described, using terms such as "vegetable flavoring". Although they are approved for human consumption no studies assess the short-term or long-term effects of inhaling them. As of 2016 their safety had not been assessed by the US Flavor and Extract Manufacturers Association (FEMA). As of 2018 the majority of flavorings in e-liquids had not been investigated for inhalation toxicity.{{rp|Summary, 4}} A 2017 review stated that FEMAhad identified 1037 flavoring agents as potential respiratory hazards due to volatility and respiratory irritant properties. Common flavoring agents on that list include diacetyl, acetoin, 2,3-pentanedione (buttery), camphor and cyclohexanone (minty), benzaldehyde (cherry or almond), cinnamaldehyde (cinnamon), cresol (leathery) or medicinal (chocolate), and isoamyl acetate (banana). As of 2017 the four most commonly reported flavoring additives were vanillin, ethyl maltol, ethyl vanillin, and menthol. A 2017 review stated, "the implication by manufacturers that flavoring ingredients used in e-cigarettes and related devices (e.g. hookahs) are safe for inhalation because they have FEMA GRAS™ status for use in food has been stated to be 'false and misleading' by FEMA."{{cite journal |vauthors=Wolff MS, Buckley JP, Engel SM, McConnell RS, Barr DB |date=April 2017 |title=Emerging exposures of developmental toxicants |journal=Current Opinion in Pediatrics |volume=29 |issue=2 |pages=218–224 |doi=10.1097/MOP.0000000000000455 |pmc=5473289 |pmid=28059904}}

Many flavorings are irritants. {{rp|3}} The limited available data suggest that the majority of flavorings could lead to significant health risks from long-term use, particularly those that are sweet. Some e-liquids contain large amounts of flavorings. A 2016 study of 30 e-cigarette products in the US market reported that 13 were more than 1% flavoring chemicals by weight, some of which were of potential toxicological concern (e.g., cause respiratory irritation).{{cite journal |vauthors=Zare S, Nemati M, Zheng Y |year=2018 |title=A systematic review of consumer preference for e-cigarette attributes: Flavor, nicotine strength, and type |journal=PLOS ONE |volume=13 |issue=3 |pages=e0194145 |bibcode=2018PLoSO..1394145Z |doi=10.1371/journal.pone.0194145 |pmc=5854347 |pmid=29543907 |doi-access=free}}{{CC-notice|cc=by4|url=http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0194145|vauthors=Zare S, Nemati M, Zheng Y}} Some flavorings are toxic and some resemble known carcinogens. A 2016 study of five flavorings across six types of e-cigarettes reported that flavorings significantly affected the in vitro toxicity profile. Some artificial flavorings are known cytotoxins. Unflavored vapor is less cytotoxic than flavored vapor.{{rp|82}} A 2012 study reported that in embryonic and adult cellular models, some flavorings not reported in tobacco smoke were cytotoxic.{{cite journal |vauthors=Naik P, Cucullo L |date=October 2015 |title=Pathobiology of tobacco smoking and neurovascular disorders: untied strings and alternative products |journal=Fluids and Barriers of the CNS |volume=12 |issue=1 |page=25 |doi=10.1186/s12987-015-0022-x |pmc=4628383 |pmid=26520792 |doi-access=free}} The caffeine exposures from vaping are considerably less than caffeinated beverages. Limited information is available regarding the effects of inhaling caffeine.{{rp|Other Toxicants, Caffeine; 197}} The evidence is unclear that particular flavorings carry health risks, though some may increase such risks.{{rp|19}}

Cinnamaldehyde has been described as highly cytotoxic. Cinnamaldehyde has been detected in flavorings such as cinnamon, tobacco, sweet (e.g. caramel), and fruit.{{rp|Exposure to Flavorings, 175}} A 2014 review concluded that cinnamaldehyde was cytotoxic at amounts 400 times less than those allowed EPA. Coffee and cinnamon flavorings are reported to be the most toxic.{{cite journal |vauthors=Jankowski M, Brożek G, Lawson J, Skoczyński S, Zejda JE |date=May 2017 |title=E-smoking: Emerging public health problem? |journal=International Journal of Occupational Medicine and Environmental Health |volume=30 |issue=3 |pages=329–344 |doi=10.13075/ijomeh.1896.01046 |pmid=28481369 |doi-access=free}} A 2017 review concluded that they were carcinogenic or toxic, and could contribute to cardiopulmonary diseases and neurodegenerative disorders. Only sparse evidence directly associates cinnamon inhalations with asthma. Some e-liquids containing cinnamaldehyde stimulate TRPA1, which might induce effects on the lung. In human lung fibroblasts, cinnamon roll flavoring resulted in a noticeable rise in the amount of inflammatory cytokine IL-8.

A 2019 case report described an 18-year-old patient using a Juul device with mint-flavored pods in the days before episodes of pneumothorax.{{cite journal |vauthors=Bonilla A, Blair AJ, Alamro SM, Ward RA, Feldman MB, Dutko RA, Karagounis TK, Johnson AL, Folch EE, Vyas JM |date=September 2019 |title=Recurrent spontaneous pneumothoraces and vaping in an 18-year-old man: a case report and review of the literature |journal=Journal of Medical Case Reports |volume=13 |issue=1 |page=283 |doi=10.1186/s13256-019-2215-4 |pmc=6732835 |pmid=31495337 |doi-access=free}}{{CC-notice|cc=by4|url=https://jmedicalcasereports.biomedcentral.com/articles/10.1186/s13256-019-2215-4|vauthors=Bonilla A, Blair AJ, Alamro SM, Ward RA, Feldman MB, Dutko RA, Karagounis TK, Johson AL, Folch EE, Vyas JM}} A 2019 study that sampled e-cigarette delivery systems reported that Juul pods were the only product to demonstrate in vitro cytotoxicity from both nicotine and flavoring chemical content, in particular ethyl maltol. As of 2017 limited data described the effects of menthol inhalation. Some flavorings may increase lung toxicity or lung inflammation in part by producing free radicals and inflammation.

E-liquids contain possibly toxic aldehydes and reactive oxygen species (ROS). Many flavorings are known aldehydes, such as anisaldehyde, cinnamaldehyde, and isovaleraldehyde. Saccharides in sweet e-liquid flavorings generate furans and aldehydes when vaporized.{{rp|FLAVORINGS, 172}} The consequences of aldehyde-containing flavorings on pulmonary surfaces are unknown. A 2012 study reported that butterscotch flavoring was highly toxic with one liquid while two others had low toxicity. A 2014 in vitro study showed that menthol flavorings have a damaging effect on human periodontal ligament fibroblast growth. Methanol increased the amount of hydrogen peroxide. A 2017 study reported a variety of flavoring-initiated inflammatory cytokines in lung cell cultures, of which acetoin and maltol were among the strongest. A 2014 in vitro study demonstrated that vaping of a balsamic flavoring without nicotine activated the release of proinflammatory cytokines in lung epithelial cells and keratinocytes. Other additives may reduce the irritation on the pharynx. It is possible that flavorings may worsen harmful effects such as diminished cell viability, escalated rates of apoptosis, escalated DNA strand breaks, alterations in cell morphology and intensified inflammatory mediator production.

Flavorings that contain diacetyl and acetyl propionyl are used for butter, chocolate, milk, toffee,{{cite journal |vauthors=Hildick-Smith GJ, Pesko MF, Shearer L, Hughes JM, Chang J, Loughlin GM, Ipp LS |date=December 2015 |title=A Practitioner's Guide to Electronic Cigarettes in the Adolescent Population |journal=The Journal of Adolescent Health |volume=57 |issue=6 |pages=574–579 |doi=10.1016/j.jadohealth.2015.07.020 |pmid=26422289 |doi-access=free}} or menthol flavorings. Diacetyl occurs in flavorings such as caramel, butterscotch, watermelon, pina colada, and strawberry. A 2016 study reported that 39 of 51 flavored e-cigarettes contained diacetyl.{{cite web |author=Editorial Staff |date=7 July 2016 |title=Popcorn Lung: A Dangerous Risk of Flavored E-Cigarettes |url=http://www.lung.org/about-us/blog/2016/07/popcorn-lung-risk-ecigs.html |publisher=American Lung Association}} The American Lung Association recommended in 2016 that the FDA require that diacetyl and other chemicals be banned from e-cigarettes. Diacetyl and acetyl propionyl are associated with bronchiolitis obliterans. A 2018 PHE report stated that e-liquids containing diacetyl are not likely to present a considerable risk.{{rp|159}} A 2015 review recommended specific regulation of diacetyl and acetyl propionyl, which have been associated with respiratory harm when inhaled.{{cite journal |vauthors=Farsalinos KE, Le Houezec J |year=2015 |title=Regulation in the face of uncertainty: the evidence on electronic nicotine delivery systems (e-cigarettes) |journal=Risk Management and Healthcare Policy |volume=8 |pages=157–167 |doi=10.2147/RMHP.S62116 |pmc=4598199 |pmid=26457058 |doi-access=free}} Exposure to diacetyl produces morphological liver alterations according to animal studies. Diacetyl and acetyl-propionyl have been reported in concentrations above those recommended by the US National Institute for Occupational Safety and Health. Diacetyl is reported at lower levels in e-cigarettes than in traditional cigarettes.

2, 3-pentanedione is an α-diketone that is chemically and structurally similar to diacetyl. A 2016 report stated that it had become a popular replacement for diacetyl, although it had been shown to cause airway epithelial damage similar to diacetyl. A 2016 review concluded that liquids that use butyric acid in place of diacetyl and acetyl propionyl, could have negative health effects.{{cite book |url=https://books.google.com/books?id=j20kDAAAQBAJ |title=Analytical Assessment of e-Cigarettes: From Contents to Chemical and Particle Exposure Profiles |vauthors=Farsalinos KE, Gillman IG, Hecht SS, Polosa R, Thornburg J |date=16 November 2016 |publisher=Elsevier Science |isbn=978-0-12-811242-7 |page=22}} Another 2016 review surfaced concerns that e-liquid additives might lead to diseases such as popcorn lung.

Cherry flavorings contain a benzaldehyde, a main ingredient for many fruit flavorings. Benzaldehyde can irritate the eyes and respiratory mucous membranes.{{cite journal |vauthors=Dhand R |date=July 2017 |title=Inhaled Drug Therapy 2016: The Year in Review |journal=Respiratory Care |volume=62 |issue=7 |pages=978–996 |doi=10.4187/respcare.05624 |pmid=28559466 |doi-access=free}} The irritants butyl acetate, diethyl carbonate, benzoic acid, quinoline, bis(2-ethylhexyl) phthalate, and 2,6-dimethyl phenol were present as undeclared ingredients in the e-liquid. A 2010 study reported weight loss drug rimonabant in e-liquids. The drug has been linked to seizures and suicides. The same study reported that e-liquid can contain amino-tadalafil which is a component of Cialis, used for erectile dysfunction. This and other pharmacologic compounds present some degree of risk.{{rp|Other Toxicants, Pharmaceutical Drugs; 197}}

In 2015 CDC tested 36 e-cigarette products for 10 flavoring compounds commonly used as additives in tobacco products. Measurable levels of eucalyptol and pulegone were reported in menthol-flavored varieties for all manufacturers. Menthol concentrations ranged from 3,700 to 12,000 μg/g, similar to those reported in traditional cigarettes. Menthol was reported at low concentrations in 40% of the tobacco-flavored nonmenthol products tested. Other flavoring compounds reported were camphor, methyl, salicylate, pulegone, cinnamaldehyde (CAD), and eugenol. A 2016 study analyzed 30 e-cigarette products and reported that 13 contained more than 1% flavoring chemicals by weight. Among the chemicals identified were aldehydes (e.g., benzaldehyde and vanillin), which are primary respiratory tract irritants. Tobacco-flavored e-liquids were derived from flavoring chemicals (e.g., bubble gum and cotton candy flavoring) rather than tobacco extract. Various candy and fruit flavored e-liquids exhibited cytotoxic or mutagenic effects in vitro.

IARC categorized formaldehyde as a human carcinogen, and acetaldehyde is categorized as a potential human carcinogen. Formaldehyde induced DNA damage and inhibited DNA repair. Acetaldehyde generated DNA crosslinking, which impedes metabolic functions, including DNA replication, repair, recombination, transcription and chromatin remodeling.{{cite journal |vauthors=Huang SJ, Xu YM, Lau AT |date=June 2018 |title=Electronic cigarette: A recent update of its toxic effects on humans |journal=Journal of Cellular Physiology |volume=233 |issue=6 |pages=4466–4478 |doi=10.1002/jcp.26352 |pmid=29215738 |s2cid=3556795}} Aldehydes may cause harm. A 2016 study reported that e-liquids without flavoring generated no aldehydes, which indicated that flavorings were causing the creation of aldehydes, according to a 2018 PHE report.{{rp|160}}

Chemicals can be inadvertently produced, especially carbonyls such as formaldehyde, acetaldehyde, acrolein, and glyoxal when the nichrome wire (heating element) reaches a high enough temperature. Potentially hazardous carbonyls have been identified in aerosols at temperatures above 200 °C. Propylene glycol-containing liquids produced the most amounts of carbonyls. A 2014 study reported toxic chemical vapor levels at 1 to 2 orders of magnitude smaller than with cigarette smoke, but greater than from a nicotine inhaler. A 2015 study reported toxic and irritation-causing carbonyls, although measured levels of toxic chemicals were inconsistent. The study reported that toxicant levels may be higher than with cigarette smoke.

A 2017 study reported that battery output voltage positively influenced carbonyl vapor levels. A 2015 study reported that e-cigarettes using higher voltages (5.0 V) can emit carcinogens including formaldehyde at levels comparable to cigarette smoke, creating a lifetime cancer risk 5 to 15 times greater than long-term smoking. while lower voltages (3.0 V) produce levels of formaldehyde and acetaldehyde roughly 13 and 807-fold less than in cigarette smoke. Elevated aldehyde formation has an unpleasant taste, leading users to avoid it. The average amount of formaldehyde in vapor from high-voltage devices is higher than the average from cigarettes.{{cite journal |vauthors=Zborovskaya Y |date=February 2017 |title=E-Cigarettes and Smoking Cessation: A Primer for Oncology Clinicians |journal=Clinical Journal of Oncology Nursing |volume=21 |issue=1 |pages=54–63 |doi=10.1188/17.CJON.54-63 |pmid=28107337 |s2cid=206992720}} Another 2015 study reported that "dripping", where the e-liquid is dripped directly onto the atomizer, can create carbonyls.{{cite journal |vauthors=Born H, Persky M, Kraus DH, Peng R, Amin MR, Branski RC |date=July 2015 |title=Electronic Cigarettes: A Primer for Clinicians |journal=Otolaryngology–Head and Neck Surgery |volume=153 |issue=1 |pages=5–14 |doi=10.1177/0194599815585752 |pmid=26002957 |s2cid=10199442}}

The amount of formaldehyde expected to be inhaled by the user is disputed. In 2015 PHE reported that normal vaping generates low levels of aldehydes. Normal usage also generates low levels of formaldehyde.{{rp|77, 82}} However, users detect and avoid the "dry puff", leading them to conclude, "There is no indication that EC users are exposed to dangerous levels of aldehydes."{{rp|77–78}} In 2018 PHE reported that at normal temperatures, aldehyde levels were negligible compared with smoke.{{rp|158}}

{{Excerpt|Nicotine#Adverse effects}}

E-cigarettes increase serum nicotine levels quicker than nicotine replacement products, but more gradually than traditional cigarettes.{{cite journal |vauthors=Marsot A, Simon N |date=March 2016 |title=Nicotine and Cotinine Levels With Electronic Cigarette: A Review |journal=International Journal of Toxicology |volume=35 |issue=2 |pages=179–185 |doi=10.1177/1091581815618935 |pmid=26681385 |s2cid=12969599 |doi-access=free}} A 2014 review concluded that e-cigarettes have a pharmacokinetic nicotine profile closer to nicotine replacement products than to traditional cigarettes.{{cite journal |vauthors=Schivo M, Avdalovic MV, Murin S |date=February 2014 |title=Non-cigarette tobacco and the lung |journal=Clinical Reviews in Allergy & Immunology |volume=46 |issue=1 |pages=34–53 |doi=10.1007/s12016-013-8372-0 |pmid=23673789 |s2cid=23626872}}

Another 2014 review concluded that serum cotinine levels were comparable to traditional cigarettes,{{cite journal |vauthors=Callahan-Lyon P |date=May 2014 |title=Electronic cigarettes: human health effects |journal=Tobacco Control |volume=23 |issue=Supplement 2 |pages=ii36–ii40 |doi=10.1136/tobaccocontrol-2013-051470 |pmc=3995250 |pmid=24732161}} but varied by usage pattern and device.

A 2017 study reported that vaping produced comparable levels of nicotine urinary metabolites to tobacco and smokeless tobacco products. However, oxidative nicotine metabolites were less in vapers.

A 2017 review concluded that some vaping products delivered the same amount of nicotine as traditional cigarettes.{{cite journal |vauthors=England LJ, Aagaard K, Bloch M, Conway K, Cosgrove K, Grana R, Gould TJ, Hatsukami D, Jensen F, Kandel D, Lanphear B, Leslie F, Pauly JR, Neiderhiser J, Rubinstein M, Slotkin TA, Spindel E, Stroud L, Wakschlag L |date=January 2017 |title=Developmental toxicity of nicotine: A transdisciplinary synthesis and implications for emerging tobacco products |journal=Neuroscience and Biobehavioral Reviews |volume=72 |pages=176–189 |doi=10.1016/j.neubiorev.2016.11.013 |pmc=5965681 |pmid=27890689}}

In 2018 the National Academies of Sciences, Engineering, and Medicine reported that the degree of dependence is less for e-cigarettes than traditional cigarettes.{{rp|Summary, Conclusion 8-2.; 7}}

{{Main|Composition of electronic cigarette aerosol}}

The chemical composition of e-cigarette aerosols varies. As of 2014 limited chemistry data existed. E-cigarette aerosol is generated when the e-liquid reaches a temperature of roughly 100–250 °C within a chamber, which causes pyrolysis and possible decomposition of other liquid ingredients. The levels of nicotine, TSNAs, aldehydes, metals, volatile organic compounds (VOCs), flavorings, and tobacco alkaloids in e-cigarette vapors vary greatly. The yield of chemicals reported in the e-cigarette vapor varies depending on, several factors, including the e-liquid contents, puffing rate, and the battery voltage.

E-cigarettes consist of fine and ultrafine particles of particulate matter, in the form of an aerosol. The aerosol (mist) produced by an e-cigarette is commonly but inaccurately called vapor. In physics, a vapor is a substance in the gas phase whereas an aerosol is a suspension of tiny particles of liquid, solid or both within a gas. The word "vaping" is not technically accurate when applied to e-cigarettes.{{cite journal |vauthors=Offermann F |date=June 2014 |title=The Hazards of E-Cigarettes |url=http://bookstore.ashrae.biz/journal/journal_s_article.php?articleID=1539 |journal=ASHRAE Journal |volume=56 |issue=6}}{{Dead link|date=August 2019|bot=InternetArchiveBot|fix-attempted=yes}} The aerosol is made-up of liquid sub-micron particles of condensed vapor; thus, the users of these devices are rather "aerosolizing." This aerosol that is produces looks like cigarette smoke to some extent. After a puff, inhalation of the aerosol travels from the device into the mouth and lungs. The composition of e-liquids varies widely due to the extensive range of nicotine levels and flavoring additives used in these products, which result in a variety of chemical combinations.

A 2014 review concluded that the particles produced from vaping are comparable in particle-size distribution and number of particles to cigarette smoke, with the majority in the ultrafine range. Some e-cigarettes released more particles than cigarette smoke. Fine particles can be chemically intricate and non-uniform. Particle composition and size was mostly unknown. These uncertainties limited the ability to compare e-cigarette vapor and traditional cigarettes. In 2014 WHO reported e-cigarettes release a lower concentration of particles than traditional cigarettes.

As of 2014 evidence on the long-term exposure of metals was limited. Metals including nickel, cadmium,{{cite journal |vauthors=Bourke L, Bauld L, Bullen C, Cumberbatch M, Giovannucci E, Islami F, McRobbie H, Silverman DT, Catto JW |date=June 2017 |title=E-cigarettes and Urologic Health: A Collaborative Review of Toxicology, Epidemiology, and Potential Risks |journal=European Urology |volume=71 |issue=6 |pages=915–923 |doi=10.1016/j.eururo.2016.12.022 |pmid=28073600 |hdl-access=free |hdl=1893/24937}} lead, chromium, nickel, tin, and silicate have been reported in e-cigarette vapor. The device could contribute small amounts of metals in the liquid and vapor, because their metal parts contact the e-liquid.

A 2014 review concluded that it was unlikely that metal contamination was a serious health risk. A 2018 PHE report stated, "[e-cigarettes] that generate minimal metal emissions should become an industry standard."{{rp|162}} In 2014 the American Heart Association referenced low levels of metals in emissions. A 2014 review concluded metal particls from various components of e-cigarettes appeared in vapor, with potential exposures higher than smoke. A 2013 study reported metal particles in the aerosol were at levels 10-50 times less than permitted in inhalation medicines. A 2014 review found no evidence of vapor contamination with metals that would justify a health concern.

A 2016 study reported that metals can be carcinogenic, nephrotoxic, neurotoxic, and hemotoxic. A 2018 study reported that copper nanoparticles can induce mitochondrial and DNA injury in lung fibroblasts. DNA repair can be impeded by vaporized titanium dioxide nanoparticles as demonstrated by single-strand DNA breaks and oxidative stress in the DNA of A549 cells.{{cite journal |vauthors=Kaur G, Pinkston R, Mclemore B, Dorsey WC, Batra S |date=March 2018 |title=Immunological and toxicological risk assessment of e-cigarettes |journal=European Respiratory Review |volume=27 |issue=147 |page=170119 |doi=10.1183/16000617.0119-2017 |pmc=9489161 |pmid=29491036 |doi-access=free}} Heavy metals are correlated with serious health issues. Inhaling lead can induce serious neurologic injury, notably to the growing brains of children.

A 2015 report by the American College of Physicians stated that metals may adversely affect the nervous system.{{cite journal |vauthors=Crowley RA |date=April 2015 |title=Electronic nicotine delivery systems: executive summary of a policy position paper from the American College of Physicians |journal=Annals of Internal Medicine |volume=162 |issue=8 |pages=583–584 |doi=10.7326/M14-2481 |pmid=25894027 |s2cid=207538290 |doi-access=}} A 2016 review concluded that metals reported in vapor may induce cell damage and initiate inflammatory cytokine such as in human lung fibroblasts. A 2017 review concluded, "E-cigarette aerosols and copper nanoparticles induced mitochondrial ROS production, mitochondrial stress (reduced stability of OxPhos electron transport chain (ETC) complex IV subunit) and DNA fragmentation in lung fibroblasts." A 2013 review concluded that metallic nanoparticles are associated with respiratory distress and disease.{{cite journal |vauthors=Kleinstreuer C, Feng Y |date=September 2013 |title=Lung deposition analyses of inhaled toxic aerosols in conventional and less harmful cigarette smoke: a review |journal=International Journal of Environmental Research and Public Health |volume=10 |issue=9 |pages=4454–4485 |doi=10.3390/ijerph10094454 |pmc=3799535 |pmid=24065038 |doi-access=free}} A 2017 review linked cadmium to low sperm density.

A 2023 review concluded that the evidence about metals in vapor was not sufficient to create a firm conclusion. It highlighted that prior smoking history was not always appropriately considered in these studies due to long half-life for some metals.{{Cite journal |last1=Jia-You |first1=Gong |last2=Ghosh |first2=Manosij |last3=Hoet |first3=Peter |date=October 2023 |title=Association between metal exposure from e-cigarette components and toxicity endpoints: A literature review |url=https://www.sciencedirect.com/science/article/abs/pii/S0273230023001563 |journal=Regulatory Toxicology and Pharmacology |volume=144 |issue=105488 |doi=10.1016/j.yrtph.2023.105488 |pmid=37657743|url-access=subscription }}

Compared to traditional cigarettes, older devices typically produced much lower blood nicotine levels, although a 2014 study reported plasma nicotine concentration which comparable to that of traditional cigarettes. A 2014 study reported that nicotine delivered from e-cigarettes entered the body slower than traditional cigarettes. A 2014 review concluded that inexperienced users obtained moderate amounts of nicotine from e-cigarettes.{{cite journal |vauthors=Schroeder MJ, Hoffman AC |date=May 2014 |title=Electronic cigarettes and nicotine clinical pharmacology |journal=Tobacco Control |volume=23 |issue=Supplement 2 |pages=ii30–ii35 |doi=10.1136/tobaccocontrol-2013-051469 |pmc=3995273 |pmid=24732160}}

Tank or adjustable e-cigarettes, as well as concentrated nicotine liquids, may deliver nicotine at levels similar to traditional cigarettes. The American Heart Association reported in 2014 that some e-cigarette tank devices with stronger batteries achieve higher temperatures, which may raise nicotine levels. A 2017 study reported that nicotine delivery compared to previous generation had increased by 35-72%, elevating heart rates comparable to traditional cigarettes.{{cite journal |vauthors=Benowitz NL, Burbank AD |date=August 2016 |title=Cardiovascular toxicity of nicotine: Implications for electronic cigarette use |journal=Trends in Cardiovascular Medicine |volume=26 |issue=6 |pages=515–523 |doi=10.1016/j.tcm.2016.03.001 |pmc=4958544 |pmid=27079891}} As of 2017 fourth-generation devices had not been heavily researched.

File:Recolored_Overview_of_reward_structures_in_the_human_brain2.png, such as nicotine, is associated with its ability to excite the mesolimbic and dopaminergic systems.{{cite journal |vauthors=Di Matteo V, Pierucci M, Di Giovanni G, Benigno A, Esposito E |year=2007 |title=The neurobiological bases for the pharmacotherapy of nicotine addiction |journal=Current Pharmaceutical Design |volume=13 |issue=12 |pages=1269–1284 |doi=10.2174/138161207780618920 |pmid=17504235}} How do e-cigarettes affect the brain?{{cite web |date=March 2018 |title=Electronic Cigarettes (E-cigarettes) |url=https://www.drugabuse.gov/publications/drugfacts/electronic-cigarettes-e-cigarettes |publisher=National Institute on Drug Abuse}}{{PD-notice}} The nicotine in e-liquids readily absorbs into the bloodstream when a person uses an e-cigarette. Upon entering the blood, nicotine stimulates the adrenal glands to release the hormone epinephrine (adrenaline). Epinephrine stimulates the central nervous system and increases blood pressure, breathing, and heart rate. As with most addictive substances, nicotine increases levels of a chemical messenger in the brain called dopamine, which affects parts of the brain that control reward (pleasure from natural behaviors such as eating). These feelings motivate some people to use nicotine again and again, despite possible risks to their health and well-being.]]

The health effects of long-term nicotine use are unknown. While myriad studies have been conducted, many questions remain unresolved, including impurities in e-liquids,{{rp|Minor Tobacco Alkaloids, 193}} effects of nicotine,{{cite journal |vauthors=Mishra A, Chaturvedi P, Datta S, Sinukumar S, Joshi P, Garg A |year=2015 |title=Harmful effects of nicotine |journal=Indian Journal of Medical and Paediatric Oncology |volume=36 |issue=1 |pages=24–31 |doi=10.4103/0971-5851.151771 |pmc=4363846 |pmid=25810571 |doi-access=free}}

File:FDA_Announces_Regulatory_Plan_to_Shift_Trajectory_of_Tobacco-related_Disease_and_Death.webm Commissioner Scott Gottlieb announced on 28 July 2017 a comprehensive regulatory plan for tobacco and nicotine regulation that will serve as a multi-year roadmap to better protect youth and significantly reduce tobacco-related disease and death, including pursuing lowering nicotine in regular cigarettes to a minimally or non-addictive level.{{cite web |date=15 March 2018 |title=FDA's Plan for Tobacco and Nicotine Regulation |url=https://www.fda.gov/TobaccoProducts/NewsEvents/ucm568425.htm |archive-url=https://web.archive.org/web/20170801224017/https://www.fda.gov/TobaccoProducts/NewsEvents/ucm568425.htm |url-status=dead |archive-date=1 August 2017 |publisher=United States Food and Drug Administration}}{{PD-notice}}]]

Exposure to e-cigarette components in a susceptible time period of brain development could induce persistent behavioral changes. The FDA stated in 2019 that some vapers experienced seizures; most reports involved youth or young adult users.

A 2016 review concluded that pregnant/breastfeeding women should not substitute cigarettes with e-cigarettes due to the uncertainty about ingredients. The FDA has not approved e-cigarettes as a smoking cessation aid.{{Cite web |last=CDC |date=2024-05-20 |title=E-Cigarettes and Pregnancy |url=https://www.cdc.gov/maternal-infant-health/pregnancy-substance-abuse/e-cigarettes.html |access-date=2024-07-31 |website=Maternal Infant Health |language=en-us}} One study reported increased irritability among infants in those exposed to e-cigarettes or smoking.{{Citation |title=E-cigarettes (Vaping) |date=July 2023 |work=Mother To Baby {{!}} Fact Sheets |url=http://www.ncbi.nlm.nih.gov/books/NBK582524/ |access-date=2024-07-30 |place=Brentwood (TN) |publisher=Organization of Teratology Information Specialists (OTIS) |pmid=35951787}}

A 2022 study recommended quitting smoking altogether through smoking cessation therapy rather than turning to e-cigarettes as an alternative.{{Cite journal |last1=Hajek |first1=Peter |last2=Przulj |first2=Dunja |last3=Pesola |first3=Francesca |last4=Griffiths |first4=Chris |last5=Walton |first5=Robert |last6=McRobbie |first6=Hayden |last7=Coleman |first7=Tim |last8=Lewis |first8=Sarah |last9=Whitemore |first9=Rachel |last10=Clark |first10=Miranda |last11=Ussher |first11=Michael |last12=Sinclair |first12=Lesley |last13=Seager |first13=Emily |last14=Cooper |first14=Sue |last15=Bauld |first15=Linda |date=May 2022 |title=Electronic cigarettes versus nicotine patches for smoking cessation in pregnancy: a randomized controlled trial |journal=Nature Medicine |language=en |volume=28 |issue=5 |pages=958–964 |doi=10.1038/s41591-022-01808-0 |issn=1546-170X |pmc=9117131 |pmid=35577966}} The U.S. Preventive Services Task Force (USPSTF) recommended that pregnant women adopt behavioral interventions for quitting.{{Cite web |date=19 January 2021 |title=Tobacco Smoking Cessation in Adults, Including Pregnant Persons: Interventions |url=https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/tobacco-use-in-adults-and-pregnant-women-counseling-and-interventions |access-date=31 July 2024 |website=U.S. Preventative Services Task Force}}

A 2017 review noted that the public found vaping to be safer than smoking.{{cite journal |vauthors=Fracol M, Dorfman R, Janes L, Kulkarni S, Bethke K, Hansen N, Kim J |date=November 2017 |title=The Surgical Impact of E-Cigarettes: A Case Report and Review of the Current Literature |journal=Archives of Plastic Surgery |volume=44 |issue=6 |pages=477–481 |doi=10.5999/aps.2017.00087 |pmc=5801784 |pmid=29069879}}

A 2014 review concluded that few users are concerned about potential adverse health effects. A 2016 German survey reported that 21% consider vaping to be less harmful than smoking, 46% just as harmful, 16% thought they were more harmful, while 17% gave no answer.{{rp|189}} {{As of|2018}}, under 50% of adults in the UK believe vaping is less harmful than smoking.{{rp|20}}

A 2014 worldwide survey reported that 88% of respondents perceived vaping to be less harmful than smoking and 11% believed that vaping was absolutely harmless.{{cite journal |vauthors=Tomashefski A |date=September 2016 |title=The perceived effects of electronic cigarettes on health by adult users: A state of the science systematic literature review |journal=Journal of the American Association of Nurse Practitioners |volume=28 |issue=9 |pages=510–515 |doi=10.1002/2327-6924.12358 |pmid=26997487 |s2cid=42900184}}

The largest age group contributing to the use and purchase of e-cigarettes are young adults, which include an age range from teens to 30's. A questionnaire examining college students demonstrated that current users believe that e-cigarettes are more convenient and taste and smell better than traditional tobacco products. Another notable result was the trend among current electronic cigarette users to have reported no previous use of tobacco. This would be contraindicative of what the original claims of e-cigarettes manufacturers when they were introduced to the market. While a majority of electronic cigarette users state the understanding of possible harm to their health, there is also the belief that they are safer than other forms of tobacco.{{Cite journal |last1=Kelsh |first1=Shelby |last2=Ottney |first2=Anne |last3=Young |first3=Mark |last4=Kelly |first4=Michelle |last5=Larson |first5=Rodney |last6=Sohn |first6=Minji |date=2023-03-07 |title=Young Adults' Electronic Cigarette Use and Perceptions of Risk |journal=Tobacco Use Insights |volume=16 |pages=1179173X231161313 |doi=10.1177/1179173X231161313 |issn=1179-173X |pmc=9996725 |pmid=36911177}}

A 2015 PHE report noted a nation-wide US survey among adults that reported 11% thought vaping during pregnancy was less harmful than smoking, 51% thought it was as harmful, 12% thought it was more harmful, while 26% were unsure.{{rp|190}} A 2017 review concluded that the majority of survey respondents perceived vaping can carry health risks to mother and child, and that vaping was less harmful than smoking.{{cite journal |vauthors=McCubbin A, Fallin-Bennett A, Barnett J, Ashford K |date=February 2017 |title=Perceptions and use of electronic cigarettes in pregnancy |journal=Health Education Research |volume=32 |issue=1 |pages=22–32 |doi=10.1093/her/cyw059 |pmc=5914445 |pmid=28158490}}

Over the 2015-2017 period, multiple surveys reported that youth believe vaping to be a safe substitute for smoking.{{cite journal |vauthors=Schneider S, Diehl K |date=May 2016 |title=Vaping as a Catalyst for Smoking? An Initial Model on the Initiation of Electronic Cigarette Use and the Transition to Tobacco Smoking Among Adolescents |journal=Nicotine & Tobacco Research |volume=18 |issue=5 |pages=647–653 |doi=10.1093/ntr/ntv193 |pmid=26386472 |doi-access=}}{{cite journal |vauthors=McCausland K, Maycock B, Leaver T, Jancey J |date=February 2019 |title=The Messages Presented in Electronic Cigarette-Related Social Media Promotions and Discussion: Scoping Review |journal=Journal of Medical Internet Research |volume=21 |issue=2 |pages=e11953 |doi=10.2196/11953 |pmc=6379814 |pmid=30720440 |doi-access=free}}{{CC-notice|cc=by4|url=https://www.jmir.org/2019/2/e11953/|author(s)=Kahlia McCausland, Bruce Maycock, Tama Leaver, and Jonine Jancey}} A 2016 study reported that flavored vapes reduced the perception of tobacco use danger among youth. Another 2016 study reported that tobacco flavor increased harm perception while fruit and sweet flavors decreased harm perception among UK adolescents. Similarly, a 2016 study in the US reported that, for US adolescents, fruit-flavored e-cigarettes were perceived to be less harmful than tobacco flavored ones. E-cigarettes were the most commonly used nicotine delivery system youth as of the 2023 National Youth Tobacco Survey. E-cigarette use in high school students was reported to be decreasing despite increasing in middle school; about 2.8 million American youth use any tobacco product.{{Cite journal |last=Products |first=Center for Tobacco |date=2024-06-26 |title=Results from the Annual National Youth Tobacco Survey |url=https://www.fda.gov/tobacco-products/youth-and-tobacco/results-annual-national-youth-tobacco-survey |journal=FDA |language=en}}{{dead link|date=May 2025|bot=medic}}{{cbignore|bot=medic}}{{Cite journal |last1=Aly |first1=Ameera Syafiqah |last2=Mamikutty |first2=Rokiah |last3=Marhazlinda |first3=Jamaludin |date=2022-10-31 |title=Association between Harmful and Addictive Perceptions of E-Cigarettes and E-Cigarette Use among Adolescents and Youth—A Systematic Review and Meta-Analysis |journal=Children |volume=9 |issue=11 |page=1678 |doi=10.3390/children9111678 |issn=2227-9067 |pmc=9689130 |pmid=36360406 |doi-access=free}}

Ecigs vaped by pregnant women may increase copd and asthma risk in offspring.{{Cite web |last=Malesu |first=Vijay Kumar |date=2025-02-27 |title=Vaping while pregnant isn't harmless—study uncovers risks to newborn lung health |url=https://www.news-medical.net/news/20250227/Vaping-while-pregnant-isnt-harmlesse28094study-uncovers-risks-to-newborn-lung-health.aspx |access-date=2025-06-07 |website=News-Medical |language=en}}

Data from two states in the Pregnancy Risk Assessment System (PRAMS) show that in 2015—roughly the mid-point of the study period—10.8% of the sample used e-cigarettes in the three months prior to the pregnancy while 7.0%, 5.8%, and 1.4% used these products at the time of the pregnancy, in the first trimester, and at birth respectively.{{cite journal |last1=Kapaya |first1=Martha |title=Use of Electronic Vapor Products Before, During, and After Pregnancy Among Women with a Recent Live Birth — Oklahoma and Texas, 2015 |journal=MMWR. Morbidity and Mortality Weekly Report |language=en-us |doi=10.15585/mmwr.mm6808a1 |date=2019|volume=68 |issue=8 |pages=189–194 |pmid=30817748 |pmc=6394383 }} According to National Health Interview Survey (NHIS) data from 2014 to 2017, 38.9% of pregnant smokers used e-cigarettes compared to only 13.5% of non-pregnant, reproductive age women smokers.{{cite journal |last1=Liu |first1=Buyun |last2=Xu |first2=Guifeng |last3=Rong |first3=Shuang |last4=Santillan |first4=Donna A. |last5=Santillan |first5=Mark K. |last6=Snetselaar |first6=Linda G. |last7=Bao |first7=Wei |title=National Estimates of e-Cigarette Use Among Pregnant and Nonpregnant Women of Reproductive Age in the United States, 2014-2017 |journal=JAMA Pediatrics |date=2019 |volume=173 |issue=6 |pages=600–602 |doi=10.1001/jamapediatrics.2019.0658 |pmid=31034001 |pmc=6547070 |issn=2168-6211}} A health economic study found that passing an e-cigarette minimum legal sale age law in the United States increased teenage prenatal smoking by 0.6 percentage points and had no effect on birth outcomes.{{cite journal |last1=Pesko |first1=Michael F. |last2=Currie |first2=Janet M. |title=E-cigarette minimum legal sale age laws and traditional cigarette use among rural pregnant teenagers |journal=Journal of Health Economics |date=1 July 2019 |volume=66 |pages=71–90 |pmid=31121389 |pmc=7051858 |doi=10.1016/j.jhealeco.2019.05.003 |issn=0167-6296}}

According to the CDC, E-cigarettes are not safe during pregnancy. "Although the aerosol of e-cigarettes generally has fewer harmful substances than cigarette smoke, e-cigarettes and other products containing nicotine are not safe to use during pregnancy. Nicotine is a health danger for pregnant women and developing babies and can damage a developing baby's brain and lungs. Also, some of the flavorings used in e-cigarettes may be harmful to a developing baby."{{Cite web |url= https://www.cdc.gov/reproductivehealth/maternalinfanthealth/substance-abuse/e-cigarettes-pregnancy.htm |title=E-Cigarettes and Pregnancy |website=Centers for Disease Control |date=March 2019}}

A popular vaporizer named Juul was widely used by American young people until 2022, when the FDA banned its products from sale.{{cite news |last1=Sampath |first1=Uday |last2=Tanna |first2=Shivani |last3=Sharma |first3=Akriti |title=Juul ban put on hold as FDA starts additional review |url=https://www.reuters.com/business/healthcare-pharmaceuticals/juul-gets-temporary-reprieve-us-fda-ban-2022-07-06/ |access-date=15 January 2023 |work=Reuters |date=6 July 2022}}{{cite news|url=https://www.washingtontimes.com/news/2018/apr/25/juul-maker-popular-e-cigarettes-invests-30m-youth-/|title=JUUL, maker of popular e-cigarettes, invests $30M in youth awareness|author=Laura Kelly and Tom Howell Jr.|work=The Washington Times|date=25 April 2018}} Close to 80% of respondents in a 2017 Truth Initiative study aged 15–24 reported using Juul also used the device in the last 30 days.{{cite journal|last1=Willett|first1=Jeffrey G|last2=Bennett|first2=Morgane|last3=Hair|first3=Elizabeth C|last4=Xiao|first4=Haijuan |last5=Greenberg |first5=Marisa S|last6=Harvey|first6=Emily|last7=Cantrell|first7=Jennifer|last8=Vallone|first8=Donna |title=Recognition, use and perceptions of JUUL among youth and young adults|journal=Tobacco Control |volume=28|issue=1|pages=tobaccocontrol–2018–054273|date=18 April 2018|doi=10.1136/tobaccocontrol-2018-054273|pmid=29669749|s2cid=4953543|url=https://truthinitiative.org/sites/default/files/Recognition-use-and-perceptions-of-JUUL-among-youth-and-young-adults.pdf|archive-date=7 December 2018|archive-url=https://web.archive.org/web/20181207152101/https://truthinitiative.org/sites/default/files/Recognition-use-and-perceptions-of-JUUL-among-youth-and-young-adults.pdf|url-status=dead}}

File:Burn_with_an_electronic_cigarette-2_HTML.png|alt=E-cigarette battery explosion.

File:Burn_with_an_electronic_cigarette-4_HTML.png|alt=E-cigarette battery explosion.

• Health effects of tobacco
• Regulation of e-cigarettes
• Positions of medical organizations on e-cigarettes
• List of tobacco-related topics

{{Reflist|refs=

{{cite journal | vauthors = Hartmann-Boyce J, Chepkin SC, Ye W, Bullen C, Lancaster T | title = Nicotine replacement therapy versus control for smoking cessation | journal = The Cochrane Database of Systematic Reviews | volume = 5 | pages = CD000146 | date = May 2018 | issue = 5 | pmid = 29852054 | pmc = 6353172 | doi = 10.1002/14651858.CD000146.pub5 | quote = There is high-quality evidence that all of the licensed forms of NRT (gum, transdermal patch, nasal spray, inhalator and sublingual tablets/lozenges) can help people who make a quit attempt to increase their chances of successfully stopping smoking. NRTs increase the rate of quitting by 50% to 60%, regardless of setting, and further research is very unlikely to change our confidence in the estimate of the effect. The relative effectiveness of NRT appears to be largely independent of the intensity of additional support provided to the individual.
A meta-analysis of adverse events associated with NRT included 92 RCTs and 28 observational studies, and addressed a possible excess of chest pains and heart palpitations among users of NRT compared with placebo groups (Mills 2010). The authors report an OR of 2.06 (95% CI 1.51 to 2.82) across 12 studies. We replicated this data collection exercise and analysis where data were available (included and excluded) in this review, and detected a similar but slightly lower estimate, OR 1.88 (95% CI 1.37 to 2.57; 15 studies; 11,074 participants; OR rather than RR calculated for comparison; Analysis 6.1). Chest pains and heart palpitations were an extremely rare event, occurring at a rate of 2.5% in the NRT groups compared with 1.4% in the control groups in the 15 trials in which they were reported at all. A recent network meta-analysis of cardiovascular events associated with smoking cessation pharmacotherapies (Mills 2014), including 21 RCTs comparing NRT with placebo, found statistically significant evidence that the rate of cardiovascular events with NRT was higher (RR 2.29 95% CI 1.39 to 3.82). However, when only serious adverse cardiac events (myocardial infarction, stroke and cardiovascular death) were considered, the finding was not statistically significant (RR 1.95 95% CI 0.26 to 4.30). }}

{{cite web |date=July 2017 |title=Electronic Cigarette Fires and Explosions in the United States 2009 – 2016 |url=https://www.usfa.fema.gov/downloads/pdf/publications/electronic_cigarettes.pdf |publisher=United States Fire Administration |pages=1–56}}{{PD-notice}}

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• {{Commons category-inline|Electronic cigarettes}}

{{Electronic cigarettes}}

{{Authority control}}{{Use dmy dates|date=February 2025}}

Category:Electronic cigarettes

Category:Product safety