Passive smoking#Industry-funded studies and critiques

Fritz Lickint created the term "passive smoking" ("Passivrauchen") in a publication in the German language during the 1930s. {{cite journal |url=https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(14)70064-5/fulltext |title=Fritz Lickint |last=Gourd |first=Katherine |date=2014 |journal=The Lancet. Respiratory Medicine |volume=2 |issue=5 |pages=358–359 |publisher=The Lancet |doi=10.1016/S2213-2600(14)70064-5 |pmid=24726404 |access-date=7 December 2023 |quote=}}{{cite web |url=https://www.afro.who.int/sites/default/files/2017-09/Chapter%2032.%20The%20history%20of%20tobacco.pdf |title=Chapter 32 History of Tobacco |author= |date=2017 |website=www.afro.who.int |publisher=World Health Organization |access-date=7 December 2023 |quote=}}{{cite journal |last1= Brawley |first1=Otis W. |last2=Glynn |first2=Thomas J.|last3=Khuri|first3=Fadlo R.|last4= Wender|first4=Richard C. |date=18 November 2013 |title=The first surgeon general's report on smoking and health: The 50th anniversary |journal=CA |volume=64 |issue=1 |pages=5–8 |doi= 10.3322/caac.21210 |pmid=24249254 |doi-access=free }} Terms used include "environmental tobacco smoke" to refer to the airborne matter, while "involuntary smoking" and "passive smoking" refer to exposure to secondhand smoke.{{cite web |title=Health Effects of Exposure to Secondhand Smoke |url=http://www.epa.gov/smokefree/healtheffects.html |url-status=dead |archive-url=https://web.archive.org/web/20150905193507/http://www.epa.gov/smokefree/healtheffects.html |archive-date=5 September 2015 |access-date=6 September 2015 |publisher=United States Environmental Protection Agency}}{{cite journal|last1=Chapman|first1=S.|title=Other people's smoke: what's in a name?|journal=Tobacco Control|date=1 June 2003|volume=12|issue=2|pages=113–4|doi=10.1136/tc.12.2.113 |pmid=12773710 |pmc=1747703}} The term "environmental tobacco smoke" can be traced back to a 1974 industry-sponsored meeting held in Bermuda, while the term "passive smoking" was first used in the title of a scientific paper in 1970. The Surgeon General of the United States prefers to use the phrase "secondhand smoke" rather than "environmental tobacco smoke", stating that "The descriptor 'secondhand' captures the involuntary nature of the exposure, while 'environmental' does not."{{rp|9}} Most researchers consider the term "passive smoking" to be synonymous with "secondhand smoke". In contrast, a 2011 commentary in Environmental Health Perspectives argued that research into "thirdhand smoke" renders it inappropriate to refer to passive smoking with the term "secondhand smoke", which the authors stated constitutes a pars pro toto.{{cite journal|last1=Protano|first1=Carmela|last2=Vitali|first2=Matteo|title=The New Danger of Thirdhand Smoke: Why Passive Smoking Does Not Stop at Secondhand Smoke|journal=Environmental Health Perspectives|date=1 October 2011|volume=119|issue=10|pages=a422|doi=10.1289/ehp.1103956 |pmid=21968336 |pmc=3230455 }}

The term "sidestream smoke" is sometimes used to refer to smoke that goes into the air directly from a burning cigarette, cigar, or pipe,{{harvnb|IARC|2004|p=1191}}: "During smoking of cigarettes, cigars, pipes and other tobacco productions, in addition to the mainstream smoke drawn and inhaled by the smokers, a stream of smoke is released between puffs into the air from the burning cone. Once released, this stream (also known as the sidestream smoke) is mixed with exhaled mainstream smoke as well as the air in an indoor environment to form the secondhand smoke to which ..." while "mainstream smoke" refers to smoke that a smoker exhales.

Secondhand smoke causes many of the same diseases as direct smoking, including cardiovascular diseases, lung cancer, and respiratory diseases.{{cite report |author1=California Environmental Protection Agency: Air Resources Board |title=Proposed Identification of Environmental Tobacco Smoke as a Toxic Air Contaminant |date=24 June 2005 |url=https://escholarship.org/uc/item/8hk6960q }} These include:

• Cancer:
• General: overall increased risk;{{harvnb|Surgeon General|2006|pp=30–46}} reviewing the evidence accumulated on a worldwide basis, the International Agency for Research on Cancer concluded in 2004 that "Involuntary smoking (exposure to secondhand or 'environmental' tobacco smoke) is carcinogenic to humans." The Centers for Disease Control and Prevention reports that about 70 chemicals present in secondhand smoke are carcinogenic.{{cite web |title=Secondhand Smoke (SHS) Facts |url=https://www.cdc.gov/tobacco/data_statistics/fact_sheets/secondhand_smoke/general_facts/index.htm |website=CDC |date=5 January 2021 |access-date=August 5, 2021}}
• Lung cancer: Passive smoking is a risk factor for lung cancer.{{cite journal|last1=Alberg|first1=Anthony J.|last2=Brock|first2=Malcolm V.|last3=Ford|first3=Jean G.|last4=Samet|first4=Jonathan M.|last5=Spivack|first5=Simon D.|title=Epidemiology of Lung Cancer|journal=Chest|date=1 May 2013|volume=143|issue=5_suppl|pages=e1S–e29S |pmid=23649439 |pmc=4694610 |doi=10.1378/chest.12-2345 }}{{cite journal |last1=Bhatnagar|first1=A |last2=Whitsel|first2=LP |last3=Ribisl|first3=KM| last4=Bullen|first4=C |last5=Chaloupka|first5=F |last6=Piano|first6=MR |last7=Robertson|first7=RM |last8=McAuley|first8=T |last9=Goff|first9=D |last10=Benowitz|first10=N |last11=((American Heart Association Advocacy Coordinating Committee, Council on Cardiovascular and Stroke Nursing, Council on Clinical Cardiology, and Council on Quality of Care and Outcomes))|first11=Research|title=Electronic cigarettes: a policy statement from the American Heart Association |journal=Circulation|date=14 October 2014|volume=130|issue=16|pages=1418–36|doi=10.1161/CIR.0000000000000107|pmid=25156991|pmc=7643636 |s2cid=16075813 |url=https://escholarship.org/uc/item/52p2317d }} In the United States, secondhand smoke is estimated to cause more than 7,000 deaths from lung cancer a year among non-smokers.{{cite web|title=Health Effects of Secondhand Smoke|url=https://www.cdc.gov/tobacco/data_statistics/fact_sheets/secondhand_smoke/health_effects/|access-date=30 May 2015|date=November 24, 2014}} A quarter of all cases occur in people who have never smoked.{{Cite journal |last1=Pallis |first1=Athanasios G. |last2=Syrigos |first2=Konstantinos N. |date=December 2013 |title=Lung cancer in never smokers: Disease characteristics and risk factors |url=http://dx.doi.org/10.1016/j.critrevonc.2013.06.011 |journal=Critical Reviews in Oncology/Hematology |volume=88 |issue=3 |pages=494–503 |doi=10.1016/j.critrevonc.2013.06.011 |pmid=23921082 |issn=1040-8428}}
• Breast cancer: The California Environmental Protection Agency concluded in 2005 that passive smoking increases the risk of breast cancer in younger, primarily premenopausal females by 70% and the US Surgeon General has concluded that the evidence is "suggestive", but still insufficient to assert such a causal relationship. In contrast, the International Agency for Research on Cancer concluded in 2004 that there was "no support for a causal relation between involuntary exposure to tobacco smoke and breast cancer in never-smokers." A 2015 meta-analysis found that the evidence that passive smoking moderately increased the risk of breast cancer had become "more substantial than a few years ago".{{cite journal |last1=Macacu |first1=Alina |last2=Autier |first2=Philippe |last3=Boniol |first3=Mathieu |last4=Boyle |first4=Peter |title=Active and passive smoking and risk of breast cancer: a meta-analysis |journal=Breast Cancer Research and Treatment |date=November 2015 |volume=154 |issue=2 |pages=213–224 |doi=10.1007/s10549-015-3628-4 |pmid=26546245 |s2cid=4680641 |url=https://strathprints.strath.ac.uk/55324/1/Macacu_etal_BCRT_2015_Active_and_passive_smoking_and_risk_of_breast_cancer.pdf }}
• Cervical cancer: A 2015 overview of systematic reviews found that exposure to secondhand smoke increased the risk of cervical cancer.
• Bladder cancer: A 2016 systematic review and meta-analysis found that secondhand smoke exposure was associated with a significant increase in the risk of bladder cancer.{{cite journal|last1=Cumberbatch|first1=Marcus G.|last2=Rota|first2=Matteo|last3=Catto|first3=James W.F.|last4=La Vecchia|first4=Carlo|title=The Role of Tobacco Smoke in Bladder and Kidney Carcinogenesis: A Comparison of Exposures and Meta-analysis of Incidence and Mortality Risks|journal=European Urology|date=September 2016|volume=70|issue=3|pages=458–466 |pmid=26149669 |doi=10.1016/j.eururo.2015.06.042 |url=http://eprints.whiterose.ac.uk/88607/8/WRRO_88607.pdf}}
• Circulatory system: risk of heart disease{{harvnb|Surgeon General|2006|loc=Ch. 8}}{{cite journal|last1=Lv|first1=X|last2=Sun|first2=J|last3=Bi|first3=Y|last4=Xu|first4=M|last5=Lu|first5=J|last6=Zhao|first6=L|last7=Xu|first7=Y|title=Risk of all-cause mortality and cardiovascular disease associated with secondhand smoke exposure: a systematic review and meta-analysis|journal=International Journal of Cardiology|date=15 November 2015|volume=199|pages=106–15|doi=10.1016/j.ijcard.2015.07.011|pmid=26188829}} and reduced heart rate variability.{{cite journal|last1=Dinas|first1=PC|last2=Koutedakis|first2=Y|last3=Flouris|first3=AD|title=Effects of active and passive tobacco cigarette smoking on heart rate variability |journal=International Journal of Cardiology|date=20 February 2013|volume=163|issue=2|pages=109–15|doi=10.1016/j.ijcard.2011.10.140|pmid=22100604}}
• Epidemiological studies have shown that both active and passive cigarette smoking increase the risk of atherosclerosis.{{cite journal |last1=Zou |first1=N |last2=Hong |first2=J |last3=Dai |first3=QY |title=Passive cigarette smoking induces inflammatory injury in human arterial walls |journal=Chinese Medical Journal |date=20 February 2009 |volume=122 |issue=4 |pages=444–448 |doi=10.3760/cma.j.issn.0366-6999.2009.04.0016 |pmid=19302752 |doi-access=free }}
• Passive smoking is strongly associated with an increased risk of stroke, and this increased risk is disproportionately high at low levels of exposure.{{cite journal |last1=Oono |first1=I.P. |last2=Mackay |first2=D.F. |last3=Pell |first3=J.P. |title=Meta-analysis of the association between secondhand smoke exposure and stroke |journal=Journal of Public Health |date=December 2011 |volume=33 |issue=4 |pages=496–502 |doi=10.1093/pubmed/fdr025 |pmid=21422014 |doi-access=free }}
• Lung problems:
• Risk of asthma{{harvnb|Surgeon General|2006|pp=555–8}}
• Risk of chronic obstructive pulmonary disease (COPD){{cite journal |last1=Bentayeb |first1=Malek |last2=Simoni |first2=Marzia |last3=Norback |first3=Dan |last4=Baldacci |first4=Sandra |last5=Maio |first5=Sara |last6=Viegi |first6=Giovanni |last7=Annesi-Maesano |first7=Isabella |title=Indoor air pollution and respiratory health in the elderly |journal=Journal of Environmental Science and Health, Part A |date=6 December 2013 |volume=48 |issue=14 |pages=1783–1789 |doi=10.1080/10934529.2013.826052 |pmid=24007433 |s2cid=41862447 }}
• According to a 2015 review, passive smoking may increase the risk of tuberculosis infection and accelerate the progression of the disease, but the evidence remains weak.{{cite journal |last1=Dogar |first1=O. F. |last2=Pillai |first2=N. |last3=Safdar |first3=N. |last4=Shah |first4=S. K. |last5=Zahid |first5=R. |last6=Siddiqi |first6=K. |title=Second-hand smoke and the risk of tuberculosis: a systematic review and a meta-analysis |journal=Epidemiology and Infection |date=November 2015 |volume=143 |issue=15 |pages=3158–3172 |doi=10.1017/S0950268815001235 |pmid=26118887 |pmc=9150979 |s2cid=206285892 }}
• The majority of studies on the association between secondhand smoke exposure and sinusitis have found a significant association between the two.{{cite journal |last1=Hur |first1=Kevin |last2=Liang |first2=Jonathan |last3=Lin |first3=Sandra Y. |title=The role of secondhand smoke in sinusitis: a systematic review: Sinusitis and secondhand smoke |journal=International Forum of Allergy & Rhinology |date=January 2014 |volume=4 |issue=1 |pages=22–28 |doi=10.1002/alr.21232 |pmid=24574074 |s2cid=9537143|doi-access=free }}
• Cognitive impairment and dementia: Exposure to secondhand smoke may increase the risk of cognitive impairment and dementia in adults 50 and over.{{cite journal|last1=Chen|first1=R|last2=Hu|first2=Z|last3=Orton|first3=S|last4=Chen|first4=RL|last5=Wei|first5=L|title=Association of passive smoking with cognitive impairment in nonsmoking older adults: a systematic literature review and a new study of Chinese cohort |journal=Journal of Geriatric Psychiatry and Neurology|date=December 2013|volume=26|issue=4|pages=199–208|doi=10.1177/0891988713496165|pmid=23877565|hdl=2436/621630|s2cid=43097513|hdl-access=free}} Children exposed to secondhand smoke show reduced vocabulary and reasoning skills when compared with non-exposed children as well as more general cognitive and intellectual deficits.{{cite journal |last1=Ling |first1=Jonathan |last2=Heffernan |first2=Thomas |title=The Cognitive Deficits Associated with Second-Hand Smoking |journal=Frontiers in Psychiatry |date=24 March 2016 |volume=7 |page=46 |doi=10.3389/fpsyt.2016.00046 |pmid=27047401 |pmc=4805605 |doi-access=free }}
• Mental health: Exposure to secondhand smoke is associated with an increased risk of depressive symptoms.{{cite journal|last1=Zeng|first1=Yan-Ni|last2=Li|first2=Ya-Min|title=Secondhand smoke exposure and mental health in adults: a meta-analysis of cross-sectional studies|journal=Social Psychiatry and Psychiatric Epidemiology|date=10 December 2015|volume=51|issue=9|pages=1339–48|doi=10.1007/s00127-015-1164-5 |pmid=26661619|s2cid=7772929}}
• During pregnancy:
• Miscarriage: a 2014 meta-analysis found that maternal secondhand smoke exposure increased the risk of miscarriage by 11%.{{cite journal|last1=Pineles|first1=B. L.|last2=Park|first2=E.|last3=Samet|first3=J. M.|title=Systematic Review and Meta-Analysis of Miscarriage and Maternal Exposure to Tobacco Smoke During Pregnancy|journal=American Journal of Epidemiology|date=10 February 2014|volume=179|issue=7|pages=807–823|doi=10.1093/aje/kwt334|pmid=24518810|pmc=3969532}}
• Low birth weight^{, part B, ch. 3}.{{harvnb|Surgeon General|2006|pp=198–205}}
• Premature birth^{, part B, ch. 3}{{cite journal|last1=Cui|first1=H|last2=Gong|first2=TT|last3=Liu|first3=CX|last4=Wu|first4=QJ|title=Associations between Passive Maternal Smoking during Pregnancy and Preterm Birth: Evidence from a Meta-Analysis of Observational Studies|journal=PLOS ONE|date=25 January 2016|volume=11|issue=1|pages=e0147848|doi=10.1371/journal.pone.0147848|pmid=26808045|pmc=4726502|bibcode=2016PLoSO..1147848C|doi-access=free}} (Evidence of the causal link is described only as "suggestive" by the US Surgeon General in his 2006 report.{{harvnb|Surgeon General|2006|pp=194–7}}) Laws limiting smoking decrease premature births.{{cite journal|last1=Been|first1=Jasper|title=Effect of smoke-free legislation on perinatal and child health: a systematic review and meta-analysis|journal=Lancet|date=28 March 2014|doi=10.1016/S0140-6736(14)60082-9|pmid=24680633|volume=383|issue=9928|pages=1549–60|last2=Nurmatov|first2=U. B.|last3=Cox|first3=B|last4=Nawrot|first4=T. S.|last5=Van Schayck|first5=C. P.|last6=Sheikh|first6=A|s2cid=8532979}}
• Stillbirth and congenital malformations in children{{cite journal|last1=Leonardi-Bee|first1=J|last2=Britton|first2=J|last3=Venn|first3=A|title=Secondhand smoke and adverse fetal outcomes in nonsmoking pregnant women: a meta-analysis |journal=Pediatrics|date=April 2011|volume=127|issue=4|pages=734–41|doi=10.1542/peds.2010-3041|pmid=21382949|s2cid=19866471}}
• Recent studies comparing females exposed to secondhand smoke and non-exposed females, demonstrate that females exposed while pregnant have higher risks of delivering a child with congenital abnormalities, longer lengths, smaller head circumferences, and neural tube defects.{{cite journal |vauthors=Salmasi G, Grady R, Jones J, McDonald SD |title=Environmental tobacco smoke exposure and perinatal outcomes: a systematic review and meta-analyses |journal=Acta Obstet Gynecol Scand |volume=89 |issue=4 |pages=423–41 |year=2010 |pmid=20085532 |doi=10.3109/00016340903505748 |s2cid=9206564 |doi-access=free }}{{cite journal|last1=Wang|first1=Meng|last2=Wang|first2=Zhi-Ping|last3=Zhang|first3=Meng|last4=Zhao|first4=Zhong-Tang|title=Maternal passive smoking during pregnancy and neural tube defects in offspring: a meta-analysis|journal=Archives of Gynecology and Obstetrics|date=13 August 2013|volume=289|issue=3|pages=513–521 |pmid=23942772 |doi=10.1007/s00404-013-2997-3 |s2cid=6526042}}
• General:
• Worsening of asthma, allergies, and other conditions.{{cite journal |author=Janson C |title=The effect of passive smoking on respiratory health in children and adults |journal=Int J Tuberc Lung Dis |volume=8 |issue=5 |pages=510–6 |year=2004 |pmid=15137524 }} A 2014 systematic review and meta-analysis found that passive smoking was associated with a slightly increased risk of allergic diseases among children and adolescents; the evidence for an association was weaker for adults.{{cite journal|last1=Saulyte|first1=Jurgita|last2=Regueira|first2=Carlos|last3=Montes-Martínez|first3=Agustín|last4=Khudyakov|first4=Polyna|last5=Takkouche|first5=Bahi|last6=Novotny|first6=Thomas E.|title=Active or Passive Exposure to Tobacco Smoking and Allergic Rhinitis, Allergic Dermatitis, and Food Allergy in Adults and Children: A Systematic Review and Meta-Analysis|journal=PLOS Medicine|date=11 March 2014|volume=11|issue=3|pages=e1001611 |pmid=24618794 |pmc=3949681 |doi=10.1371/journal.pmed.1001611 |doi-access=free }}
• Type 2 diabetes.{{cite journal|last1=Wei|first1=X|last2=E|first2=M|last3=Yu|first3=S|title=A meta-analysis of passive smoking and risk of developing Type 2 Diabetes Mellitus |journal=Diabetes Research and Clinical Practice|date=January 2015|volume=107|issue=1|pages=9–14|doi=10.1016/j.diabres.2014.09.019|pmid=25488377}}{{cite journal|last1=Wang|first1=Y|last2=Ji|first2=J|last3=Liu|first3=YJ|last4=Deng|first4=X|last5=He|first5=QQ|title=Passive smoking and risk of type 2 diabetes: a meta-analysis of prospective cohort studies|journal=PLOS ONE|date=2013|volume=8|issue=7|pages=e69915|doi=10.1371/journal.pone.0069915|pmid=23922856|pmc=3724674|bibcode=2013PLoSO...869915W|doi-access=free}}{{cite journal|last1=Sun|first1=K|last2=Liu|first2=D|last3=Wang|first3=C|last4=Ren|first4=M|last5=Yang|first5=C|last6=Yan|first6=L|title=Passive smoke exposure and risk of diabetes: a meta-analysis of prospective studies |journal=Endocrine|date=November 2014|volume=47|issue=2|pages=421–7|doi=10.1007/s12020-014-0194-1|pmid=24532101|s2cid=3276501}} It remains unclear whether the association between passive smoking and diabetes is causal.{{cite journal|last1=Pan|first1=An|last2=Wang|first2=Yeli|last3=Talaei|first3=Mohammad|last4=Hu|first4=Frank B|last5=Wu|first5=Tangchun|title=Relation of active, passive, and quitting smoking with incident type 2 diabetes: a systematic review and meta-analysis|journal=The Lancet Diabetes & Endocrinology|date=December 2015|volume=3|issue=12|pages=958–967|doi=10.1016/S2213-8587(15)00316-2|pmid=26388413|pmc=4656094}}
• Risk of carrying Neisseria meningitidis or Streptococcus pneumoniae.
• A possible increased risk of periodontitis.{{cite journal|last1=Akinkugbe|first1=Aderonke A.|last2=Slade|first2=Gary D.|last3=Divaris|first3=Kimon|last4=Poole|first4=Charles|title=Systematic Review and Meta-analysis of the Association Between Exposure to Environmental Tobacco Smoke and Periodontitis Endpoints Among Nonsmokers|journal=Nicotine & Tobacco Research|date=November 2016|volume=18|issue=11|pages=2047–56 |pmid=27083214 |pmc=5055738 |doi=10.1093/ntr/ntw105 }}
• Overall increased risk of death in both adults, where it was estimated to kill 53,000 nonsmokers per year in the U.S in 1991,{{cite journal |vauthors=Glantz SA, Parmley WW |title=Passive smoking and heart disease. Epidemiology, physiology, and biochemistry |journal=Circulation |volume=83 |issue=1 |pages=1–12 |year=1991 |pmid=1984876 |doi=10.1161/01.cir.83.1.1|doi-access=free }}{{cite journal |vauthors=Taylor AE, Johnson DC, Kazemi H |title=Environmental tobacco smoke and cardiovascular disease. A position paper from the Council on Cardiopulmonary and Critical Care, American Heart Association |journal=Circulation |volume=86 |issue=2 |pages=699–702 |year=1992 |pmid=1638735 |doi=10.1161/01.cir.86.2.699|doi-access=free }} and in children.{{harvnb|Surgeon General|2006|pp=376–380}} The World Health Organization states that passive smoking causes about 600,000 deaths a year, and about 1% of the global burden of disease.{{cite web | url=https://www.who.int/gho/phe/secondhand_smoke/en/ | title=Second-hand smoke | website=WHO website | access-date=24 April 2015}} As of 2017, passive smoking causes about 900,000 deaths a year, which is about 1/8 of all deaths caused by smoking.{{cite news|title=The last gasp|url=https://www.economist.com/blogs/graphicdetail/2017/07/daily-chart-11|access-date=20 July 2017|newspaper=The Economist|date=19 July 2017}}
• Skin conditions: A 2016 systematic review and meta-analysis found that passive smoking was associated with a higher rate of atopic dermatitis.{{cite journal|last1=Kantor|first1=R|last2=Kim|first2=A|last3=Thyssen|first3=JP|last4=Silverberg|first4=JI|title=Association of atopic dermatitis with smoking: A systematic review and meta-analysis|journal=Journal of the American Academy of Dermatology|date=December 2016|volume=75|issue=6|pages=1119–1125.e1|pmid=27542586|doi=10.1016/j.jaad.2016.07.017|pmc=5216172}}

File:How Many Cigarettes a Day Does Your Child Smoke? (21840776552).jpg. "When a child breathes air filled with cigarette smoke it can be as bad as if he actually smoked the cigarette himself."]]

• Sudden infant death syndrome (SIDS).{{cite journal|last1=Anderson|first1=HR|last2=Cook|first2=DG|title=Passive smoking and sudden infant death syndrome: review of the epidemiological evidence |journal=Thorax|date=November 1997|volume=52|issue=11|pages=1003–9|pmid=9487351|doi=10.1136/thx.52.11.1003|pmc=1758452}} In his 2006 report, the US Surgeon General concludes: "The evidence is sufficient to infer a causal relationship between exposure to secondhand smoke and sudden infant death syndrome."{{harvnb|Surgeon General|2006|p=194}} Secondhand smoking has been estimated to be associated with 430 SIDS deaths in the United States annually.[https://web.archive.org/web/20111003141849/http://www.idph.state.ia.us/adper/common/pdf/abx/tab7_ala_second_hand_smoke.pdf "Secondhand Smoke and Children Fact Sheet", American Lung Association] August 2006.
• Asthma.{{harvnb|Surgeon General|2006|pp=311–9}}{{cite journal |vauthors=Vork KL, Broadwin RL, Blaisdell RJ |title=Developing Asthma in Childhood from Exposure to Secondhand Tobacco Smoke: Insights from a Meta-Regression |journal=Environ. Health Perspect. |volume=115 |issue=10 |pages=1394–400 |year=2007 |pmid=17938726 |pmc=2022647 |doi=10.1289/ehp.10155 }}{{cite journal|last1=Tinuoye|first1=O.|last2=Pell|first2=J. P.|last3=Mackay|first3=D. F.|title=Meta-Analysis of the Association Between Secondhand Smoke Exposure and Physician-Diagnosed Childhood Asthma|journal=Nicotine & Tobacco Research|date=28 March 2013|volume=15|issue=9|pages=1475–1483|doi=10.1093/ntr/ntt033|pmid=23539174}} Secondhand smoke exposure is also associated with an almost doubled risk of hospitalization for asthma exacerbation among children with asthma.{{cite journal|last1=Wang|first1=Zhen|last2=May|first2=Sara M.|last3=Charoenlap|first3=Suvanee|last4=Pyle|first4=Regan|last5=Ott|first5=Nancy L.|last6=Mohammed|first6=Khaled|last7=Joshi|first7=Avni Y.|title=Effects of secondhand smoke exposure on asthma morbidity and health care utilization in children: a systematic review and meta-analysis|journal=Annals of Allergy, Asthma & Immunology|date=November 2015|volume=115|issue=5|pages=396–401.e2|doi=10.1016/j.anai.2015.08.005|pmid=26411971|doi-access=free}}
• Lung infections,{{cite journal |vauthors=de Jongste JC, Shields MD |title=Cough • 2: Chronic cough in children |journal=Thorax |volume=58 |issue=11 |pages=998–1003 |year=2003 |pmid=14586058 |pmc=1746521 |doi=10.1136/thorax.58.11.998 }}{{cite journal |vauthors=Dybing E, Sanner T |title=Passive smoking, sudden infant death syndrome (SIDS) and childhood infections |journal=Hum Exp Toxicol |volume=18 |issue=4 |pages=202–5 |year=1999 |pmid=10333302|doi=10.1191/096032799678839914 |s2cid=21365217 }}{{cite journal |vauthors=DiFranza JR, Aligne CA, Weitzman M |title=Prenatal and postnatal environmental tobacco smoke exposure and children's health |journal=Pediatrics |volume=113 |issue=4 Suppl |pages=1007–15 |year=2004 |pmid=15060193 |doi=10.1542/peds.113.S3.1007 |s2cid=248349 |url=http://pediatrics.aappublications.org/content/113/Supplement_3/1007.long }} also including more severe illness with bronchiolitis and bronchitis,[https://www.cdc.gov/nccdphp/publications/factsheets/prevention/pdf/smoking.pdf Preventing Smoking and Exposure to Secondhand Smoke Before, During, and After Pregnancy] {{webarchive|url=https://web.archive.org/web/20110911020755/http://www.cdc.gov/nccdphp/publications/factsheets/Prevention/pdf/smoking.pdf |date=2011-09-11 }}. Centers for Disease Control and Prevention. July 2007. and worse outcome,{{cite journal |last1=Chatzimichael |first1=A |last2=Tsalkidis |first2=A |last3=Cassimos |first3=D |last4=Gardikis |first4=S |last5=Tripsianis |first5=G |last6=Deftereos |first6=S |last7=Ktenidou-Kartali |first7=S |last8=Tsanakas |first8=I |title=The role of breastfeeding and passive smoking on the development of severe bronchiolitis in infants |journal=Minerva Pediatrica |date=June 2007 |volume=59 |issue=3 |pages=199–206 |pmid=17519864 |url=https://www.minervamedica.it/en/journals/minerva-pediatrica/article.php?cod=R15Y2007N03A0199 }} as well as increased risk of developing tuberculosis if exposed to a carrier.{{cite journal|last1=Jafta|first1=N|last2=Jeena|first2=PM|last3=Barregard|first3=L|last4=Naidoo|first4=RN|title=Childhood tuberculosis and exposure to indoor air pollution: a systematic review and meta-analysis |journal=The International Journal of Tuberculosis and Lung Disease|date=May 2015|volume=19|issue=5|pages=596–602|doi=10.5588/ijtld.14.0686|pmid=25868030}} In the United States, it is estimated that secondhand smoke has been associated with between 150,000 and 300,000 lower respiratory tract infections in infants and children under 18 months of age, resulting in between 7,500 and 15,000 hospitalizations each year.
• Impaired respiratory function and slowed lung growth
• Allergies{{cite journal|last1=Feleszko|first1=W|last2=Ruszczyński|first2=M|last3=Jaworska|first3=J|last4=Strzelak|first4=A|last5=Zalewski|first5=BM|last6=Kulus|first6=M|title=Environmental tobacco smoke exposure and risk of allergic sensitisation in children: a systematic review and meta-analysis |journal=Archives of Disease in Childhood|date=November 2014|volume=99|issue=11|pages=985–92|doi=10.1136/archdischild-2013-305444|pmid=24958794|s2cid=206856566}}
• Maternal passive smoking increases the risk of non-syndromic orofacial clefts by 50% among their children.{{cite journal|last1=Sabbagh|first1=HJ|last2=Hassan|first2=MH|last3=Innes|first3=NP|last4=Elkodary|first4=HM|last5=Little|first5=J|last6=Mossey|first6=PA|title=Passive smoking in the etiology of non-syndromic orofacial clefts: a systematic review and meta-analysis|journal=PLOS ONE|date=2015|volume=10|issue=3|pages=e0116963|doi=10.1371/journal.pone.0116963|pmid=25760440|pmc=4356514|bibcode=2015PLoSO..1016963S|doi-access=free}}
• Learning difficulties, developmental delays, executive function problems,{{cite journal|last1=Pagani|first1=Linda S.|title=Environmental tobacco smoke exposure and brain development: The case of attention deficit/hyperactivity disorder|journal=Neuroscience & Biobehavioral Reviews|date=July 2014|volume=44|pages=195–205|doi=10.1016/j.neubiorev.2013.03.008|pmid=23545330|s2cid=20470659}} and neurobehavioral effects.{{cite web|url=http://www.iceh.org/pdfs/LDDI/LDDIStatement.pdf |title=Scientific Consensus Statement on Environmental Agents Associated with Neurodevelopmental Disorders |publisher=The Collaborative on Health and the Environment's Learning and Developmental Disabilities Initiative |date=July 1, 2008 |archive-url=https://web.archive.org/web/20090327101820/http://www.iceh.org/pdfs/LDDI/LDDIStatement.pdf |url-status=dead |archive-date=2009-03-27 }}{{cite journal |last1=Chen |first1=Ruoling |last2=Clifford |first2=Angela |last3=Lang |first3=Linda |last4=Anstey |first4=Kaarin J. |title=Is exposure to secondhand smoke associated with cognitive parameters of children and adolescents?—a systematic literature review |journal=Annals of Epidemiology |date=October 2013 |volume=23 |issue=10 |pages=652–661 |doi=10.1016/j.annepidem.2013.07.001 |pmid=23969303 |doi-access=free |hdl=1885/10932 |hdl-access=free }} Animal models suggest a role for nicotine and carbon monoxide in neurocognitive problems.
• Increased risk of middle ear infections.{{harvnb|Surgeon General|2006|pp=293–309}}{{cite journal |last1=Jones |first1=Laura L. |last2=Hassanien |first2=A |last3=Cook |first3=DG |last4=Britton |first4=J |last5=Leonardi-Bee |first5=J |title=Parental Smoking and the Risk of Middle Ear Disease in Children: A Systematic Review and Meta-analysis |journal=Archives of Pediatrics & Adolescent Medicine |date=1 January 2012 |volume=166 |issue=1 |pages=18–27 |doi=10.1001/archpediatrics.2011.158 |pmid=21893640 |doi-access=free }}
• Invasive meningococcal disease.{{cite journal |last1=Lee |first1=Chien-Chang |last2=Middaugh |first2=Nicole A. |last3=Howie |first3=Stephen R. C. |last4=Ezzati |first4=Majid |title=Association of Secondhand Smoke Exposure with Pediatric Invasive Bacterial Disease and Bacterial Carriage: A Systematic Review and Meta-analysis |journal=PLOS Medicine |date=7 December 2010 |volume=7 |issue=12 |pages=e1000374 |doi=10.1371/journal.pmed.1000374 |pmid=21151890 |pmc=4595077 |bibcode=2015PLoSO..1039907C |doi-access=free }}{{cite journal|last1=Lee|first1=Chien-Chang|last2=Middaugh|first2=Nicole A.|last3=Howie|first3=Stephen R. C.|last4=Ezzati|first4=Majid|last5=Lanphear|first5=Bruce P.|title=Association of Secondhand Smoke Exposure with Pediatric Invasive Bacterial Disease and Bacterial Carriage: A Systematic Review and Meta-analysis|journal=PLOS Medicine|date=7 December 2010|volume=7|issue=12|pages=e1000374|doi=10.1371/journal.pmed.1000374|pmid=21151890|pmc=2998445 |doi-access=free }}
• Anesthesia complications and some negative surgical outcomes.{{cite journal|last1=Chiswell|first1=C|last2=Akram|first2=Y|title=Impact of environmental tobacco smoke exposure on anaesthetic and surgical outcomes in children: a systematic review and meta-analysis|journal=Archives of Disease in Childhood|date=February 2017|volume=102|issue=2|pages=123–130|doi=10.1136/archdischild-2016-310687|pmid=27417307|pmc=5284464}}
• Sleep disordered breathing: Most studies have found a significant association between passive smoking and sleep disordered breathing in children, but further studies are needed to determine whether this association is causal.{{cite journal|last1=Jara|first1=SM|last2=Benke|first2=JR|last3=Lin|first3=SY|last4=Ishman|first4=SL|title=The association between secondhand smoke and sleep-disordered breathing in children: a systematic review|journal=The Laryngoscope|date=January 2015|volume=125|issue=1|pages=241–7|doi=10.1002/lary.24833|pmid=25130300|s2cid=23401780}}
• Adverse effects on the cardiovascular system of children.{{cite journal|last1=Raghuveer|first1=Geetha|last2=White|first2=David A.|last3=Hayman|first3=Laura L.|last4=Woo|first4=Jessica G.|last5=Villafane|first5=Juan|last6=Celermajer|first6=David|last7=Ward|first7=Kenneth D.|last8=de Ferranti|first8=Sarah D.|last9=Zachariah|first9=Justin|title=Cardiovascular Consequences of Childhood Secondhand Tobacco Smoke Exposure: Prevailing Evidence, Burden, and Racial and Socioeconomic Disparities: A Scientific Statement From the American Heart Association|journal=Circulation|date=18 October 2016|volume=134|issue=16|pages=e336–59 |pmid=27619923 |pmc=5207215 |doi=10.1161/CIR.0000000000000443 }}

File:Exposure to secondhand smoke by age, race, and poverty level US.png

Epidemiological studies show that non-smokers exposed to secondhand smoke are at risk for many of the health problems associated with direct smoking.{{cn|date=December 2024}}

In 1992, a review estimated that secondhand smoke exposure was responsible for 35,000 to 40,000 deaths per year in the United States in the early 1980s.{{cite journal |last1=Steenland |first1=K. |title=Passive smoking and the risk of heart disease |journal=JAMA |date=1 January 1992 |volume=267 |issue=1 |pages=94–99 |doi=10.1001/jama.267.1.94 |pmid=1727204 }} The absolute risk increase of heart disease due to ETS was 2.2%, while the attributable risk percent was 23%. A 1997 meta-analysis found that secondhand smoke exposure increased the risk of heart disease by a quarter,{{cite journal |last1=Law |first1=M R |last2=Morris |first2=J K |last3=Wald |first3=N J |title=Environmental tobacco smoke exposure and ischaemic heart disease: an evaluation of the evidence |journal=BMJ |date=18 October 1997 |volume=315 |issue=7114 |pages=973–980 |doi=10.1136/bmj.315.7114.973 |pmid=9365294 |pmc=2127675 }} and two 1999 meta-analyses reached similar conclusions.{{cite journal |last1=Thun |first1=M |last2=Henley |first2=J |last3=Apicella |first3=L |title=Epidemiologic studies of fatal and nonfatal cardiovascular disease and ETS exposure from spousal smoking |journal=Environmental Health Perspectives |date=December 1999 |volume=107 |issue=suppl 6 |pages=841–846 |doi=10.1289/ehp.99107s6841 |pmid=10592140 |pmc=1566204 |jstor=3434563 }}{{cite journal |last1=He |first1=Jiang |last2=Vupputuri |first2=Suma |last3=Allen |first3=Krista |last4=Prerost |first4=Monica R. |last5=Hughes |first5=Janet |last6=Whelton |first6=Paul K. |title=Passive Smoking and the Risk of Coronary Heart Disease — A Meta-Analysis of Epidemiologic Studies |journal=New England Journal of Medicine |date=25 March 1999 |volume=340 |issue=12 |pages=920–926 |doi=10.1056/NEJM199903253401204 |pmid=10089185 |doi-access=free }}

Evidence shows that inhaled sidestream smoke, the main component of secondhand smoke, is about four times more toxic than mainstream smoke. This fact has been known to the tobacco industry since the 1980s, though it kept its findings secret.{{cite journal |vauthors=Diethelm PA, Rielle JC, McKee M |title=The whole truth and nothing but the truth? The research that Philip Morris did not want you to see |journal=Lancet |volume=366 |issue=9479 |pages=86–92 |year=2005 |pmid=15993237 |doi=10.1016/S0140-6736(05)66474-4 |s2cid=10442244 }}{{cite journal |vauthors=Schick S, Glantz S |title=Philip Morris toxicological experiments with fresh sidestream smoke: more toxic than mainstream smoke |journal=Tobacco Control |volume=14 |issue=6 |pages=396–404 |year=2005 |pmid=16319363 |doi=10.1136/tc.2005.011288 |pmc=1748121 }}{{cite journal |vauthors=Schick S, Glantz SA |title=Sidestream cigarette smoke toxicity increases with aging and exposure duration |journal=Tobacco Control |volume=15 |issue=6 |pages=424–9 |year=2006 |pmid=17130369 |doi=10.1136/tc.2006.016162 |pmc=2563675 }}{{cite journal |last1=Schick |first1=S. F. |last2=Glantz |first2=S. |title=Concentrations of the Carcinogen 4-(Methylnitrosamino)-1-(3-Pyridyl)-1-Butanone in Sidestream Cigarette Smoke Increase after Release into Indoor Air: Results from Unpublished Tobacco Industry Research |journal=Cancer Epidemiology, Biomarkers & Prevention|date=1 August 2007 |volume=16 |issue=8 |pages=1547–1553 |doi=10.1158/1055-9965.EPI-07-0210 |pmid=17684127 |s2cid=690030 |doi-access=free }} Some scientists believe that the risk of passive smoking, in particular the risk of developing coronary heart diseases, may have been substantially underestimated.{{cite journal |last1=Whincup |first1=Peter H |last2=Gilg |first2=Julie A |last3=Emberson |first3=Jonathan R |last4=Jarvis |first4=Martin J |last5=Feyerabend |first5=Colin |last6=Bryant |first6=Andrew |last7=Walker |first7=Mary |last8=Cook |first8=Derek G |title=Passive smoking and risk of coronary heart disease and stroke: prospective study with cotinine measurement |journal=BMJ |date=24 July 2004 |volume=329 |issue=7459 |pages=200–205 |doi=10.1136/bmj.38146.427188.55 |pmid=15229131 |pmc=487731 }}

In 1997, a meta-analysis on the relationship between secondhand smoke exposure and lung cancer concluded that such exposure caused lung cancer. The increase in risk was estimated to be 24% among non-smokers who lived with a smoker.{{cite journal |last1=Hackshaw |first1=A K |last2=Law |first2=M R |last3=Wald |first3=N J |title=The accumulated evidence on lung cancer and environmental tobacco smoke |journal=BMJ |date=18 October 1997 |volume=315 |issue=7114 |pages=980–988 |doi=10.1136/bmj.315.7114.980 |pmid=9365295 |pmc=2127653 }} In 2000, Copas and Shi reported that there was clear evidence of publication bias in the studies included in this meta-analysis. They further concluded that after correcting for publication bias, and assuming that 40% of all studies are unpublished, this increased risk decreased from 24% to 15%.{{cite journal |last1=Copas |first1=J B |last2=Shi |first2=JQ |title=Reanalysis of epidemiological evidence on lung cancer and passive smoking |journal=BMJ |date=12 February 2000 |volume=320 |issue=7232 |pages=417–418 |doi=10.1136/bmj.320.7232.417 |pmid=10669446 |pmc=27286 }} This conclusion has been challenged on the basis that the assumption that 40% of all studies are unpublished was "extreme".{{rp|1269}} In 2006, Takagi et al. reanalyzed the data from this meta-analysis to account for publication bias and estimated that the relative risk of lung cancer among those exposed to secondhand smoke was 1.19, slightly lower than the original estimate.{{cite journal |last1=Takagi |first1=Hisato |last2=Sekino |first2=Seishiro |last3=Kato |first3=Takayoshi |last4=Matsuno |first4=Yukihiro |last5=Umemoto |first5=Takuya |title=Revisiting evidence on lung cancer and passive smoking: Adjustment for publication bias by means of "trim and fill" algorithm |journal=Lung Cancer |date=February 2006 |volume=51 |issue=2 |pages=245–246 |doi=10.1016/j.lungcan.2005.11.004 |pmid=16386820 }} A 2000 meta-analysis found a relative risk of 1.48 for lung cancer among men exposed to secondhand smoke, and a relative risk of 1.16 among those exposed to it at work.{{cite journal |last1=Zhong |first1=Lijie |last2=Goldberg |first2=Mark S |last3=Parent |first3=Marie-Élise |last4=Hanley |first4=James A |title=Exposure to environmental tobacco smoke and the risk of lung cancer: a meta-analysis |journal=Lung Cancer |date=January 2000 |volume=27 |issue=1 |pages=3–18 |doi=10.1016/s0169-5002(99)00093-8 |pmid=10672779 }} Another meta-analysis confirmed the finding of an increased risk of lung cancer among women with spousal exposure to secondhand smoke the following year. It found a relative risk of lung cancer of 1.29 for women exposed to secondhand smoke from their spouses.{{cite journal |last1=Taylor |first1=Richard |last2=Gumming |first2=Robert |last3=Woodward |first3=Alistair |last4=Black |first4=Megan |title=Passive smoking and lung cancer: a cumulative meta-analysis |journal=Australian and New Zealand Journal of Public Health |date=June 2001 |volume=25 |issue=3 |pages=203–211 |doi=10.1111/j.1467-842x.2001.tb00564.x |pmid=11494987 |s2cid=25724906 |doi-access=free }} A 2014 meta-analysis noted that "the association between exposure to secondhand smoke and lung cancer risk is well established."{{cite journal |last1=Kim |first1=Claire H. |last2=Lee |first2=Yuan-Chin Amy |last3=Hung |first3=Rayjean J. |last4=McNallan |first4=Sheila R. |last5=Cote |first5=Michele L. |last6=Lim |first6=Wei-Yen |last7=Chang |first7=Shen-Chih |last8=Kim |first8=Jin Hee |last9=Ugolini |first9=Donatella |last10=Chen |first10=Ying |last11=Liloglou |first11=Triantafillos |last12=Andrew |first12=Angeline S. |last13=Onega |first13=Tracy |last14=Duell |first14=Eric J. |last15=Field |first15=John K. |last16=Lazarus |first16=Philip |last17=Le Marchand |first17=Loic |last18=Neri |first18=Monica |last19=Vineis |first19=Paolo |last20=Kiyohara |first20=Chikako |last21=Hong |first21=Yun-Chul |last22=Morgenstern |first22=Hal |last23=Matsuo |first23=Keitaro |last24=Tajima |first24=Kazuo |last25=Christiani |first25=David C. |last26=McLaughlin |first26=John R. |last27=Bencko |first27=Vladimir |last28=Holcatova |first28=Ivana |last29=Boffetta |first29=Paolo |last30=Brennan |first30=Paul |last31=Fabianova |first31=Eleonora |last32=Foretova |first32=Lenka |last33=Janout |first33=Vladimir |last34=Lissowska |first34=Jolanta |last35=Mates |first35=Dana |last36=Rudnai |first36=Peter |last37=Szeszenia-Dabrowska |first37=Neonila |last38=Mukeria |first38=Anush |last39=Zaridze |first39=David |last40=Seow |first40=Adeline |last41=Schwartz |first41=Ann G. |last42=Yang |first42=Ping |last43=Zhang |first43=Zuo-Feng |title=Exposure to secondhand tobacco smoke and lung cancer by histological type: A pooled analysis of the International Lung Cancer Consortium (ILCCO): Secondhand tobacco smoke and lung cancer |journal=International Journal of Cancer |date=15 October 2014 |volume=135 |issue=8 |pages=1918–1930 |doi=10.1002/ijc.28835 |pmid=24615328 |pmc=4126868 }}

A minority of epidemiologists have found it hard to understand how secondhand smoke, which is more diluted than actively inhaled smoke, could have an effect that is such a large fraction of the added risk of coronary heart disease among active smokers.{{cite journal |author=Novak K |title=Passive smoking: out from the haze |journal=Nature |volume=447 |issue=7148 |pages=1049–51 |year=2007 |pmid=17597735 |doi=10.1038/4471049a |bibcode=2007Natur.447.1049N |s2cid=9627500 |doi-access=free }}{{cite journal |last1=Bailar |first1=John C. |title=Passive Smoking, Coronary Heart Disease, and Meta-Analysis |journal=New England Journal of Medicine |date=25 March 1999 |volume=340 |issue=12 |pages=958–959 |doi=10.1056/NEJM199903253401211 |pmid=10089192 }} One proposed explanation is that secondhand smoke is not simply a diluted version of "mainstream" smoke, but has a different composition with more toxic substances per gram of total particulate matter. Passive smoking appears to be capable of precipitating the acute manifestations of cardio-vascular diseases (atherothrombosis) and may also have a negative impact on the outcome of patients who have acute coronary syndromes.{{cite journal |last1=Raupach |first1=Tobias |last2=Schäfer |first2=Katrin |last3=Konstantinides |first3=Stavros |last4=Andreas |first4=Stefan |title=Secondhand smoke as an acute threat for the cardiovascular system: a change in paradigm |journal=European Heart Journal |date=1 February 2006 |volume=27 |issue=4 |pages=386–392 |doi=10.1093/eurheartj/ehi601 |pmid=16230308 |doi-access=free }}

In 2004, the International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) reviewed all significant published evidence related to tobacco smoking and cancer. It concluded:

{{blockquote|These meta-analyses show that there is a statistically significant and consistent association between lung cancer risk in spouses of smokers and exposure to second-hand tobacco smoke from the spouse who smokes. The excess risk is of the order of 20% for women and 30% for men and remains after controlling for some potential sources of bias and confounding.}}

Subsequent meta-analyses have confirmed these findings.{{cite journal |last1=Taylor |first1=R. |last2=Najafi |first2=F. |last3=Dobson |first3=A. |title=Meta-analysis of studies of passive smoking and lung cancer: effects of study type and continent |journal=International Journal of Epidemiology |date=1 October 2007 |volume=36 |issue=5 |pages=1048–1059 |doi=10.1093/ije/dym158 |pmid=17690135 |doi-access=free }}{{cite journal |last1=Stayner |first1=Leslie |last2=Bena |first2=James |last3=Sasco |first3=Annie J. |last4=Smith |first4=Randall |last5=Steenland |first5=Kyle |last6=Kreuzer |first6=Michaela |last7=Straif |first7=Kurt |title=Lung Cancer Risk and Workplace Exposure to Environmental Tobacco Smoke |journal=American Journal of Public Health |date=March 2007 |volume=97 |issue=3 |pages=545–551 |doi=10.2105/AJPH.2004.061275 |pmid=17267733 |pmc=1805004 }}

The National Asthma Council of Australia cites studies showing that secondhand smoke is probably the most important indoor pollutant, especially around young children:{{cite web |title=Health effects of indoor air pollution |url=http://www.nationalasthma.org.au/html/management/infopapers/health_professionals/4005.asp |access-date=2006-07-26 |url-status=dead |archive-url=https://web.archive.org/web/20060805200559/http://www.nationalasthma.org.au/HTML/management/infopapers/health_professionals/4005.asp |archive-date=2006-08-05 }}

• Smoking by either parent, particularly by the mother, increases the risk of asthma in children.
• The outlook for early childhood asthma is less favourable in smoking households.
• Children with asthma who are exposed to smoking in the home generally have more severe disease.
• Many adults with asthma identify ETS as a trigger for their symptoms.
• Doctor-diagnosed asthma is more common among non-smoking adults exposed to ETS than those not exposed. Among people with asthma, higher ETS exposure is associated with a greater risk of severe attacks.

In France, exposure to secondhand smoke has been estimated to cause between 3,000{{cite journal |last1=Wirth |first1=N. |last2=Abou-Hamdan |first2=K. |last3=Spinosa |first3=A. |last4=Bohadana |first4=A. |last5=Martinet |first5=Y. |title=Le tabagisme passif |trans-title=Passive smoking |language=fr |journal=Revue de Pneumologie Clinique |date=March 2005 |volume=61 |issue=1 |pages=7–15 |doi=10.1016/s0761-8417(05)84776-5 |pmid=15772574 }} and 5,000 premature deaths per year, with the larger figure cited by Prime Minister Dominique de Villepin during his announcement of a nationwide smoke-free law: "That makes more than 13 deaths a day. It is an unacceptable reality in our country in terms of public health."{{cite news |title=France to ban smoking in public |url=http://news.bbc.co.uk/1/hi/world/europe/6032125.stm |access-date=2006-10-09 |publisher = BBC |date = 2006-10-08}}

There is good observational evidence that smoke-free legislation reduces the number of hospital admissions for heart disease.{{cite journal |last1=Meyers |first1=David G. |last2=Neuberger |first2=John S. |last3=He |first3=Jianghua |title=Cardiovascular Effect of Bans on Smoking in Public Places |journal=Journal of the American College of Cardiology |date=September 2009 |volume=54 |issue=14 |pages=1249–1255 |doi=10.1016/j.jacc.2009.07.022 |pmid=19778665 |doi-access=free }}{{cite journal |last1=Lin |first1=Hualiang |last2=Wang |first2=Hongchun |last3=Wu |first3=Wei |last4=Lang |first4=Lingling |last5=Wang |first5=Qinzhou |last6=Tian |first6=Linwei |title=The effects of smoke-free legislation on acute myocardial infarction: a systematic review and meta-analysis |journal=BMC Public Health |date=December 2013 |volume=13 |issue=1 |pages=529 |doi=10.1186/1471-2458-13-529 |pmid=23721370 |pmc=3671962 |doi-access=free }}

The International Agency for Research on Cancer of the World Health Organization concluded in 2004 that there was sufficient evidence that secondhand smoke caused cancer in humans. Those who work in environments where smoke is not regulated are at higher risk.{{cite journal |last1=Wells |first1=A J |title=Lung cancer from passive smoking at work |journal=American Journal of Public Health |date=July 1998 |volume=88 |issue=7 |pages=1025–1029 |doi=10.2105/ajph.88.7.1025 |pmid=9663148 |pmc=1508269 }} Workers particularly at risk of exposure include those in installation repair and maintenance, construction and extraction, and transportation.

Much research has come from studies of nonsmokers who are married to a smoker. The US Surgeon General, in his 2006 report, estimated that living or working in a place where smoking is permitted increases the non-smokers' risk of developing heart disease by 25–30% and lung cancer by 20–30%.{{Cite book|title = The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General|url = https://www.ncbi.nlm.nih.gov/books/NBK44324/|publisher = Centers for Disease Control and Prevention (US)|date = 2006|access-date = 2015-04-24|pmid = 20669524|series = Publications and Reports of the Surgeon General|author1 = Office on Smoking Health (US)}}

Similarly, children who are exposed to environmental tobacco smoke are shown to experience a range of adverse effects{{cite journal |last1=Pugmire |first1=Juliana |last2=Sweeting |first2=Helen |last3=Moore |first3=Laurence |title=Environmental tobacco smoke exposure among infants, children and young people: now is no time to relax |journal=Archives of Disease in Childhood |date=February 2017 |volume=102 |issue=2 |pages=117–118 |doi=10.1136/archdischild-2016-311652 |pmid=28100555 |s2cid=41806496 |doi-access=free }}{{cite journal |last1=Strachan |first1=D P |last2=Cook |first2=D G |title=Health effects of passive smoking. 1. Parental smoking and lower respiratory illness in infancy and early childhood |journal=Thorax |date=October 1997 |volume=52 |issue=10 |pages=905–914 |doi=10.1136/thx.52.10.905 |pmid=9404380 |pmc=1758431 }}{{cite journal |last1=Strachan |first1=D. P. |last2=Cook |first2=D. G. |title=Health effects of passive smoking. 4. Parental smoking, middle ear disease and adenotonsillectomy in children |journal=Thorax |date=1 January 1998 |volume=53 |issue=1 |pages=50–56 |doi=10.1136/thx.53.1.50 |pmid=9577522 |pmc=1758689 }} and a higher risk of becoming smokers later in life.{{cite journal |last1=Song |first1=Anna V. |last2=Glantz |first2=Stanton A. |last3=Halpern-Felsher |first3=Bonnie L. |title=Perceptions of Second-hand Smoke Risks Predict Future Adolescent Smoking Initiation |journal=Journal of Adolescent Health |date=December 2009 |volume=45 |issue=6 |pages=618–625 |doi=10.1016/j.jadohealth.2009.04.022 |pmid=19931835 |pmc=2814413 }} The WHO has identified reduction of exposure to environmental tobacco smoke as key element for actions to encourage healthy child development.{{cite web|access-date=2024-06-12|title=WHO Framework Convention on Tobacco Control (WHO FCTC)|url=https://www.who.int/europe/teams/tobacco/who-framework-convention-on-tobacco-control-(who-fctc)|website=www.who.int}}

The US Centers for Disease Control and Prevention monitors the extent of and trends in exposure to environmental tobacco smoke by measuring serum cotinine in national health surveys.{{cite journal |last1=Tsai |first1=James |last2=Homa |first2=David M. |last3=Gentzke |first3=Andrea S. |last4=Mahoney |first4=Margaret |last5=Sharapova |first5=Saida R. |last6=Sosnoff |first6=Connie S. |last7=Caron |first7=Kevin T. |last8=Wang |first8=Lanqing |last9=Melstrom |first9=Paul C. |last10=Trivers |first10=Katrina F. |title=Exposure to Secondhand Smoke Among Nonsmokers — United States, 1988–2014 |journal=MMWR. Morbidity and Mortality Weekly Report |date=7 December 2018 |volume=67 |issue=48 |pages=1342–1346 |doi=10.15585/mmwr.mm6748a3|pmid=30521502 |pmc=6329485 }} The prevalence of secondhand smoke exposure among U.S. nonsmokers declined from 87.5% in 1988 to 25.2% in 2014. However, nearly half of blacks and the poor were exposed in 2014.

A systematic review compared smoking control programmes and their effects on smoke exposure in children. The review distinguishes between community-based, ill-child and healthy-child settings and the most common types of interventions were counselling or brief advice during clinical visits. The review did not find superior outcomes for any intervention, and the authors caution that evidence from adult settings may not generalise well to children.{{cite journal |last1=Behbod |first1=Behrooz |last2=Sharma |first2=Mohit |last3=Baxi |first3=Ruchi |last4=Roseby |first4=Robert |last5=Webster |first5=Premila |title=Family and carer smoking control programmes for reducing children's exposure to environmental tobacco smoke |journal=Cochrane Database of Systematic Reviews |date=31 January 2018 |volume=1 |issue=1 |pages=CD001746 |doi=10.1002/14651858.CD001746.pub4 |pmid=29383710 |pmc=6491082 }}

File:Breath CO Monitor.jpg

Environmental tobacco smoke can be evaluated either by directly measuring tobacco smoke pollutants found in the air or by using biomarkers, an indirect measure of exposure. Carbon monoxide monitored through breath, nicotine, cotinine, thiocyanates, and proteins are the most specific biological markers of tobacco smoke exposure.{{cite journal |vauthors=Metz-Favre C, Donnay C, de Blay F |title=[Markers of environmental tobacco smoke (ETS) exposure] |language=fr |journal=Rev Mal Respir |volume=22 |issue=1 Pt 1 |pages=81–92 |date=February 2005 |pmid=15968761 |doi=10.1016/S0761-8425(05)85439-7 }}{{cite journal |author=McClure JB |title=Are biomarkers useful treatment aids for promoting health behavior change? An empirical review |journal=Am J Prev Med |volume=22 |issue=3 |pages=200–7 |date=April 2002 |pmid=11897465 |doi=10.1016/S0749-3797(01)00425-1 }} Biochemical tests are a much more reliable biomarker of secondhand smoke exposure than surveys. Certain groups of people are reluctant to disclose their smoking status and exposure to tobacco smoke, especially pregnant women and parents of young children. This is due to their smoking being socially unacceptable. Also, it may be difficult for individuals to recall their exposure to tobacco smoke.{{cite journal |vauthors=Klesges RC, Debon M, Ray JW |title=Are self-reports of smoking rate biased? Evidence from the Second National Health and Nutrition Examination Survey |journal=J Clin Epidemiol |volume=48 |issue=10 |pages=1225–33 |date=October 1995 |pmid=7561984 |doi=10.1016/0895-4356(95)00020-5 }}

A 2007 study in the Addictive Behaviors journal found a positive correlation between secondhand tobacco smoke exposure and concentrations of nicotine and/or biomarkers of nicotine in the body. Significant biological levels of nicotine from secondhand smoke exposure were equivalent to nicotine levels from active smoking and levels that are associated with behaviour changes due to nicotine consumption.{{cite journal |vauthors=Okoli CT, Kelly T, Hahn EJ |title=Secondhand smoke and nicotine exposure: a brief review |journal=Addict Behav |volume=32 |issue=10 |pages=1977–88 |date=October 2007 |pmid=17270359 |doi=10.1016/j.addbeh.2006.12.024 }}

Cotinine, the metabolite of nicotine, is a biomarker of secondhand smoke exposure. Typically, cotinine is measured in the blood, saliva, and urine. Hair analysis has recently become a new, noninvasive measurement technique. Cotinine accumulates in hair during hair growth, which results in a measure of long-term, cumulative exposure to tobacco smoke.{{cite journal |vauthors=Florescu A, Ferrence R, Einarson T, Selby P, Soldin O, Koren G |title=Methods for quantification of exposure to cigarette smoking and environmental tobacco smoke: focus on developmental toxicology |journal=Ther Drug Monit |volume=31 |issue=1 |pages=14–30 |date=February 2009 |pmid=19125149 |pmc=3644554 |doi=10.1097/FTD.0b013e3181957a3b }} Urinary cotinine levels have been a reliable biomarker of tobacco exposure and have been used as a reference in many epidemiological studies. However, cotinine levels found in the urine reflect exposure only over the preceding 48 hours. Cotinine levels of the skin, such as the hair and nails, reflect tobacco exposure over the previous three months and are a more reliable biomarker.

Carbon monoxide monitored via breath is also a reliable biomarker of secondhand smoke exposure as well as tobacco use. With high sensitivity and specificity, it not only provides an accurate measure, but the test is also non-invasive, highly reproducible, and low in cost. Breath CO monitoring measures the concentration of CO in an exhalation in parts per million, and this can be directly correlated to the blood CO concentration (carboxyhemoglobin).{{cite journal |vauthors=Irving JM, Clark EC, Crombie IK, Smith WC |title=Evaluation of a portable measure of expired-air carbon monoxide |journal=Prev Med |volume=17 |issue=1 |pages=109–15 |date=January 1988 |pmid=3362796 |doi=10.1016/0091-7435(88)90076-X }} Breath CO monitors can also be used by emergency services to identify patients who are suspected of having CO poisoning.

A 2004 study by the International Agency for Research on Cancer of the World Health Organization concluded that non-smokers are exposed to the same carcinogens as active smokers. Sidestream smoke contains more than 4,000 chemicals, including 69 known carcinogens. Of special concern are polynuclear aromatic hydrocarbons, tobacco-specific N-nitrosamines, and aromatic amines, such as 4-aminobiphenyl, all known to be highly carcinogenic. Mainstream smoke, sidestream smoke, and secondhand smoke contain largely the same components, however the concentration varies depending on type of smoke. Several well-established carcinogens have been shown by the tobacco companies' own research to be present at higher concentrations in sidestream smoke than in mainstream smoke.{{cite journal |vauthors=Schick S, Glantz S |title=Philip Morris toxicological experiments with fresh sidestream smoke: more toxic than mainstream smoke |journal=Tob. Control |volume=14 |issue=6 |pages=396–404 |year=2005 |pmid=16319363 |pmc=1748121 |doi=10.1136/tc.2005.011288 }}

Secondhand smoke has been shown to produce more particulate-matter (PM) pollution than an idling low-emission diesel engine. In an experiment conducted by the Italian National Cancer Institute, three cigarettes were left smoldering, one after the other, in a 60 m³ garage with a limited air exchange. The cigarettes produced PM pollution exceeding outdoor limits, as well as PM concentrations up to 10-fold that of the idling engine.{{cite journal |vauthors=Invernizzi G, Ruprecht A, Mazza R, etal |title=Particulate matter from tobacco versus diesel car exhaust: an educational perspective |journal=Tob Control |volume=13 |issue=3 |pages=219–21 |year=2004 |pmid=15333875 |pmc=1747905 |doi=10.1136/tc.2003.005975 }}

Secondhand tobacco smoke exposure has immediate and substantial effects on blood and blood vessels in a way that increases the risk of a heart attack, particularly in people already at risk.{{cite journal |vauthors=Barnoya J, Glantz SA |title=Cardiovascular effects of secondhand smoke: nearly as large as smoking |journal=Circulation |volume=111 |issue=20 |pages=2684–98 |year=2005 |pmid=15911719 |doi=10.1161/CIRCULATIONAHA.104.492215 |s2cid=2291566 |doi-access=free }} Exposure to tobacco smoke for 30 minutes significantly reduces coronary flow velocity reserve in healthy nonsmokers.{{cite journal |vauthors=Otsuka R, Watanabe H, Hirata K, etal |title=Acute effects of passive smoking on the coronary circulation in healthy young adults |journal=JAMA |volume=286 |issue=4 |pages=436–41 |year=2001 |pmid=11466122|doi=10.1001/jama.286.4.436 |doi-access=free }} Secondhand smoke is also associated with impaired vasodilation among adult nonsmokers.{{cite journal|last1=Celermajer|first1=David S.|last2=Adams|first2=Mark R.|last3=Clarkson|first3=Peter|last4=Robinson|first4=Jacqui|last5=McCredie|first5=Robyn|last6=Donald|first6=Ann|last7=Deanfield|first7=John E.|title=Passive Smoking and Impaired Endothelium-Dependent Arterial Dilatation in Healthy Young Adults|journal=New England Journal of Medicine|date=18 January 1996|volume=334|issue=3|pages=150–155|doi=10.1056/NEJM199601183340303|pmid=8531969|doi-access=free}} Secondhand smoke exposure also affects platelet function, vascular endothelium, and myocardial exercise tolerance at levels commonly found in the workplace.{{cite journal|last1=Howard|first1=G|last2=Thun|first2=MJ|title=Why is environmental tobacco smoke more strongly associated with coronary heart disease than expected? A review of potential biases and experimental data|journal=Environmental Health Perspectives|date=December 1999|volume=107|issue=Suppl 6|pages=853–8|pmid=10592142|pmc=1566209|doi=10.2307/3434565|jstor=3434565}}

Pulmonary emphysema can be induced in rats through acute exposure to sidestream tobacco smoke (30 cigarettes per day) over a period of 45 days.{{cite journal |last1=Cendon |first1=S.P. |last2=Battlehner |first2=C. |last3=Lorenzi-Filho |first3=G. |last4=Dohlnikoff |first4=M. |last5=Pereira |first5=P.M. |last6=Conceição |first6=G.M.S. |last7=Beppu |first7=O.S. |last8=Saldiva |first8=P.H.N. |title=Pulmonary emphysema induced by passive smoking: an experimental study in rats |journal=Brazilian Journal of Medical and Biological Research |date=October 1997 |volume=30 |issue=10 |pages=1241–1247 |doi=10.1590/s0100-879x1997001000017 |pmid=9496445 |doi-access=free }} Degranulation of mast cells contributing to lung damage has also been observed.{{cite journal |author1=Eren, U. |author2=Kum, S. |author3=Sandikci, M. |author4=Kara, E. |title=Effects of long-term passive smoking on the mast cells in rat lungs |journal=Revue de Médecine Vétérinaire |volume=6 |pages=319–322 |year=2006 |url=http://revmedvet.com/artdes-us.php?id=1434|archive-url=https://web.archive.org/web/20090113060853/http://revmedvet.com/artdes-us.php?id=1434|url-status=usurped|archive-date=January 13, 2009}}

The term "third-hand smoke" was recently coined to identify the residual tobacco smoke contamination that remains after the cigarette is extinguished and secondhand smoke has cleared from the air.{{cite journal |vauthors=Matt GE, Quintana PJ, Hovell MF, etal |title=Households contaminated by environmental tobacco smoke: sources of infant exposures |journal=Tob Control |volume=13 |issue=1 |pages=29–37 |date=March 2004 |pmid=14985592 |pmc=1747815 |doi= 10.1136/tc.2003.003889}}{{cite journal |vauthors=Winickoff JP, Friebely J, Tanski SE, etal |title=Beliefs about the health effects of "thirdhand" smoke and home smoking bans |journal=Pediatrics |volume=123 |issue=1 |pages=e74–9 |date=January 2009 |pmid=19117850 |doi=10.1542/peds.2008-2184 |pmc=3784302 }}{{cite news |url = https://www.nytimes.com/2009/01/03/health/research/03smoke.html |work = New York Times |title = A New Cigarette Hazard: 'Third-Hand Smoke' |first = Roni Caryn |last = Rabin |date = 2009-01-02 |access-date = 2009-01-12}} Preliminary research suggests that by-products of third-hand smoke may pose a health risk,{{cite journal |last1=Sleiman |first1=M. |last2=Gundel |first2=L. A. |last3=Pankow |first3=J. F. |last4=Jacob |first4=P. |last5=Singer |first5=B. C. |last6=Destaillats |first6=H. |title=Formation of carcinogens indoors by surface-mediated reactions of nicotine with nitrous acid, leading to potential thirdhand smoke hazards |journal=Proceedings of the National Academy of Sciences |date=13 April 2010 |volume=107 |issue=15 |pages=6576–6581 |doi=10.1073/pnas.0912820107 |pmid=20142504 |pmc=2872399 |doi-access=free }}

though the magnitude of risk, if any, remains unknown. In October 2011, it was reported that Christus St. Frances Cabrini Hospital in Alexandria, Louisiana, would seek to eliminate third-hand smoke beginning in July 2012, and that employees whose clothing smelled of smoke would not be allowed to work. This prohibition was enacted because third-hand smoke poses a special danger for the developing brains of infants and small children.[https://www.foxnews.com/us/louisiana-hospital-to-ban-odor-of-smoke-on-workers-clothes/ Louisiana Hospital to Ban Odor of Smoke on Workers' Clothes], Fox News, October 3, 2011

In 2008, there were more than 161,000 deaths attributed to lung cancer in the United States. Of these deaths, an estimated 10% to 15% were caused by factors other than first-hand smoking; equivalent to 16,000 to 24,000 deaths annually. Slightly more than half of the lung cancer deaths caused by factors other than first-hand smoking were found in nonsmokers. Lung cancer in non-smokers may well be considered one of the most common cancer mortalities in the United States. Clinical epidemiology of lung cancer has linked the primary factors closely tied to lung cancer in non-smokers as exposure to secondhand tobacco smoke, carcinogens including radon, and other indoor air pollutants.{{cite journal |last1=Samet |first1=J. M. |last2=Avila-Tang |first2=E. |last3=Boffetta |first3=P. |last4=Hannan |first4=L. M. |last5=Olivo-Marston |first5=S. |last6=Thun |first6=M. J. |last7=Rudin |first7=C. M. |title=Lung Cancer in Never Smokers: Clinical Epidemiology and Environmental Risk Factors |journal=Clinical Cancer Research |date=15 September 2009 |volume=15 |issue=18 |pages=5626–5645 |doi=10.1158/1078-0432.CCR-09-0376 |pmid=19755391 |pmc=3170525 }}

There is widespread scientific consensus that exposure to secondhand smoke is harmful.{{harvnb|Kessler|2006}} The link between passive smoking and health risks is accepted by every major medical and scientific organisation, including:

• World Health Organization
• U.S. National Institutes of Health{{cite web |url = https://ntp.niehs.nih.gov/ntp/roc/content/profiles/tobaccorelatedexposures.pdf |title = Environmental Tobacco Smoke |website = 11th Report on Carcinogens |publisher = U.S. National Institutes of Health |access-date = 2007-08-27 |url-status = live |archive-url = https://web.archive.org/web/20080716173310/http://ntp.niehs.nih.gov/ntp/roc/eleventh/profiles/s176toba.pdf |archive-date = 2008-07-16 }}
• Centers for Disease Control{{cite web |url =https://www.cdc.gov/tobacco/data_statistics/fact_sheets/secondhand_smoke/general_facts/index.htm |title = Secondhand Smoke Fact Sheet |publisher = U.S. Centers for Disease Control and Prevention |date = 2017-02-21 }}
• United States Surgeon General
• U.S. National Cancer Institute{{cite web |url = http://cancercontrol.cancer.gov/tcrb/monographs/10/index.html |title = Health Effects of Exposure to Environmental Tobacco Smoke |publisher = U.S. National Cancer Institute |access-date = 2007-08-22 |url-status = dead |archive-url = https://web.archive.org/web/20070905172350/http://cancercontrol.cancer.gov/tcrb/monographs/10/index.html |archive-date = 2007-09-05 }}
• United States Environmental Protection Agency{{cite web |url = http://www.epa.gov/smokefree/healtheffects.html |title = Health Effects of Exposure to Secondhand Smoke |publisher = United States Environmental Protection Agency |access-date = 2007-09-24}}
• California Environmental Protection Agency
• American Heart Association,{{cite web |url = http://www.americanheart.org/presenter.jhtml?identifier=3039906 |title = The Truth about Secondhand Smoke |publisher = American Heart Association |access-date = 2007-08-27}} American Lung Association,{{cite web |url = http://www.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=35422 |title = Secondhand Smoke Fact Sheet |publisher = American Lung Association |access-date = 2007-09-24 |archive-url = https://web.archive.org/web/20070918063752/http://www.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=35422 |archive-date = 2007-09-18}} and American Cancer Society{{cite web |url = http://www.cancer.org/docroot/PED/content/PED_10_2X_Secondhand_Smoke-Clean_Indoor_Air.asp |title = Secondhand Smoke |publisher = American Cancer Society |access-date = 2007-08-27 |url-status = dead |archive-url = https://web.archive.org/web/20070914162226/http://www.cancer.org/docroot/PED/content/PED_10_2X_Secondhand_Smoke-Clean_Indoor_Air.asp |archive-date = 2007-09-14 }}
• American Medical Association{{cite press release |url = http://www.ama-assn.org/ama/pub/category/16496.html |title = AMA: Surgeon General's secondhand smoke report a wake-up call to lawmakers |publisher = American Medical Association |access-date = 2007-08-27}}
• American Academy of Pediatrics{{cite web |url = http://aappolicy.aappublications.org/cgi/content/full/pediatrics%3b107/4/794 |title = Tobacco's Toll: Implications for the Pediatrician |publisher = American Academy of Pediatrics |access-date = 2007-10-02 |url-status = dead |archive-url = https://web.archive.org/web/20071015203456/http://aappolicy.aappublications.org/cgi/content/full/pediatrics;107/4/794 |archive-date = 2007-10-15 }}
• Australian National Health and Medical Research Council{{cite web |url = http://www.nphp.gov.au/publications/legislation/smoke_passive.pdf |title = National Response to Passive Smoking in Enclosed Public Places and Workplaces |publisher = Australian National Public Health Partnership |date = November 2000 |access-date = 2007-09-11 |url-status = dead |archive-url = https://web.archive.org/web/20140212191352/http://www.nphp.gov.au/publications/legislation/smoke_passive.pdf |archive-date = 2014-02-12 }}
• United Kingdom Scientific Committee on Tobacco and HealthTwo relevant reports have been published by the Scientific Committee:
• A [http://www.archive.official-documents.co.uk/document/doh/tobacco/part-2.htm 1998 report of the SCOTH] concluded that passive smoking was a cause of lung cancer, heart disease, and other health problems.
• A [http://www.dh.gov.uk/en/Publicationsandstatistics/Publications/PublicationsPolicyAndGuidance/DH_4101474 2004 update by the SCOTH] {{webarchive|url=https://web.archive.org/web/20120206182922/http://www.dh.gov.uk/en/Publicationsandstatistics/Publications/PublicationsPolicyAndGuidance/DH_4101474 |date=2012-02-06 }}, reviewing new evidence published since the 1998 report, found that recent research had confirmed the initially reported link between passive smoking and health risks.

Recent major surveys conducted by the U.S. National Cancer Institute and Centers for Disease Control have found widespread public awareness that secondhand smoke is harmful. In both 1992 and 2000 surveys, more than 80% of respondents agreed with the statement that secondhand smoke was harmful. A 2001 study found that 95% of adults agreed that secondhand smoke was harmful to children, and 96% considered tobacco-industry claims that secondhand smoke was not harmful to be untruthful.{{harvnb|Surgeon General|2006|p=588 Ch. 10}}

A 2007 Gallup poll found that 56% of respondents felt that secondhand smoke was "very harmful", a number that has held relatively steady since 1997. Another 29% believe that secondhand smoke is "somewhat harmful"; 10% answered "not too harmful", while 5% said "not at all harmful".{{cite web | url=http://www.gallup.com/poll/28216/more-smokers-feeling-harassed-smoking-bans.aspx | title=More Smokers Feeling Harassed by Smoking Bans | website=Gallup | date=25 July 2007 | access-date=20 February 2015 | author=Saad, Lydia}}

As part of its attempt to prevent or delay tighter regulation of smoking, the tobacco industry funded a number of scientific studies and, where the results cast doubt on the risks associated with secondhand smoke, sought wide publicity for those results. The industry also funded libertarian and conservative think tanks, such as the Cato Institute in the United States and the Institute of Public Affairs in Australia which criticised both scientific research on passive smoking and policy proposals to restrict smoking."[http://www.sourcewatch.org/index.php?title=Cato_Institute#Cato_and_the_tobacco_industry Cato and the tobacco industry]". Accessed 8 April 2011.Nahan, Mike. The Australian, 10 April 2000, "The IPA sings its own song". New Scientist and the European Journal of Public Health have identified these industry-wide coordinated activities as one of the earliest expressions of corporate denialism. Further, they state that the disinformation spread by the tobacco industry has created a tobacco denialism movement, sharing many characteristics of other forms of denialism, such as HIV-AIDS denialism.{{cite journal |last1=Shermer |first1=Michael |title=I am a sceptic, but I'm not a denier |journal=New Scientist |date=May 2010 |volume=206 |issue=2760 |pages=36–37 |doi=10.1016/S0262-4079(10)61210-9 |bibcode=2010NewSc.206R..36S }}{{cite journal |last1=Diethelm |first1=P. |last2=McKee |first2=M. |title=Denialism: what is it and how should scientists respond? |journal=The European Journal of Public Health |date=16 October 2008 |volume=19 |issue=1 |pages=2–4 |doi=10.1093/eurpub/ckn139 |pmid=19158101 |s2cid=8098426 |doi-access=free }}

A 2003 study by James Enstrom and Geoffrey Kabat, published in the British Medical Journal, argued that the harms of passive smoking had been overstated.{{cite journal |vauthors=Enstrom JE, Kabat GC |title=Environmental tobacco smoke and tobacco related mortality in a prospective study of Californians, 1960-98 |journal=BMJ |volume=326 |issue=7398 |page=1057 |year=2003 |pmid=12750205 |doi=10.1136/bmj.326.7398.1057 |pmc=155687 }} Their analysis reported no statistically significant relationship between passive smoking and lung cancer, coronary heart disease (CHD), or chronic obstructive pulmonary disease, though the accompanying editorial noted that "they may overemphasise the negative nature of their findings."{{cite journal |author=Davey Smith G |title=Effect of passive smoking on health: More information is available, but the controversy still persists |journal=BMJ |volume=326 |issue=7398 |pages=1048–9 |year=2003 |pmid=12750182 |doi=10.1136/bmj.326.7398.1048 |pmc=1125974 }} This paper was widely promoted by the tobacco industry as evidence that the harms of passive smoking were unproven.{{harvnb|Kessler|2006|p=1383}}{{cite journal |vauthors=Tong EK, Glantz SA |title=Tobacco industry efforts undermining evidence linking secondhand smoke with cardiovascular disease |journal=Circulation |volume=116 |issue=16 |pages=1845–54 |year=2007 |pmid=17938301 |doi=10.1161/CIRCULATIONAHA.107.715888 |s2cid=4021497 |doi-access=free }} The American Cancer Society (ACS), whose database Enstrom and Kabat used to compile their data, criticized the paper as "neither reliable nor independent", stating that scientists at the ACS had repeatedly pointed out serious flaws in Enstrom and Kabat's methodology prior to publication.{{cite press release |url = http://www.no-smoke.org/pdf/BMJrelease.pdf |title = American Cancer Society Condemns Tobacco Industry Study for Inaccurate Use of Data |publisher = American Cancer Society |date = 2003-05-13 |access-date = 2007-08-29}} Notably, the study had failed to identify a comparison group of "unexposed" persons.{{cite journal |last1=Thun |first1=Michael J |title=More misleading science from the tobacco industry |journal=BMJ |date=4 October 2003 |volume=327 |issue=7418 |pages=E237–E238 |doi=10.1136/bmjusa.03070002 |s2cid=74351979 }}

Enstrom's ties to the tobacco industry also drew scrutiny; in a 1997 letter to Philip Morris, Enstrom requested a "substantial research commitment... in order for me to effectively compete against the large mountain of epidemiologic data and opinions that already exist regarding the health effects of ETS and active smoking."{{cite web |url = http://legacy.library.ucsf.edu/tid/dfk37d00 |title = Proposed Research on the relationship of Low Levels of Active Smoking to Mortality: Letter from James Enstrom to Philip Morris Scientific Affairs office |date = 1997-01-01 |access-date = 2007-08-29}} In a US racketeering lawsuit against tobacco companies, the Enstrom and Kabat paper was cited by the US District Court as "a prime example of how nine tobacco companies engaged in criminal racketeering and fraud to hide the dangers of tobacco smoke."{{cite journal |author=Dalton R |title=Passive-smoking study faces review |journal=Nature |volume=446 |issue=7133 |pages=242 |date=March 2007 |pmid=17361147 |doi=10.1038/446242a |bibcode=2007Natur.446..242D |s2cid=27691890 |doi-access=free }} The Court found that the study had been funded and managed by the Center for Indoor Air Research,{{harvnb|Kessler|2006|p=1380}} a tobacco industry front group tasked with "offsetting" damaging studies on passive smoking, as well as by Philip Morris who stated that Enstrom's work was "clearly litigation-oriented".{{harvnb|Kessler|2006|pp=1380–3}} A 2005 paper in Tobacco Control argued that the disclosure section in the Enstrom and Kabat BMJ paper, although it met the journal's requirements, "does not reveal the full extent of the relationship the authors had with the tobacco industry."{{cite journal|last1=Bero|first1=LA|last2=Glantz|first2=S|last3=Hong|first3=MK|title=The limits of competing interest disclosures |journal=Tobacco Control|date=April 2005|volume=14|issue=2|pages=118–26|pmid=15791022|pmc=1748015}}

In 2006, Enstrom and Kabat published a meta-analysis of studies regarding passive smoking and coronary heart disease in which they reported a very weak association between passive smoking and heart disease mortality.{{cite journal|last1=Enstrom|first1=JE|last2=Kabat|first2=GC|title=Environmental tobacco smoke and coronary heart disease mortality in the United States--a meta-analysis and critique |journal=Inhalation Toxicology|date=March 2006|volume=18|issue=3|pages=199–210|doi=10.1080/08958370500434255|pmid=16399662|citeseerx=10.1.1.495.2191|s2cid=7457133}} They concluded that exposure to secondhand smoke increased the risk of death from CHD by only 5%, although this analysis has been criticized for including two previous industry-funded studies that suffered from widespread exposure misclassification.

Gio Batta Gori, a tobacco industry spokesman and consultant{{harvnb|Kessler|2006|p=162}}[http://www.usdoj.gov/civil/cases/tobacco2/20040816%20US%20FACTUAL%20MEMO%20w%20BkMks.pdf United States of America v. Philip Morris et al.], United States Factual Memorandum Pursuant to Order No. 470, Section V, United States District Court for the District of Columbia. p. 44[http://legacy.library.ucsf.edu/tid/hxh70e00 ETS / IAQ SCIENTIFIC CONSULTANTS], from the Legacy Tobacco Documents Archive. Retrieved July 19, 2007. and an expert on risk utility and scientific research, wrote in the libertarian Cato Institute's magazine Regulation that "...of the 75 published studies of ETS and lung cancer, some 70% did not report statistically significant differences of risk and are moot. Roughly 17% claim an increased risk and 13% imply a reduction of risk."{{cite journal |author=Gori, Gio Batta |title=Stoking the Rigged Terror of Secondhand Smoke |journal=Regulation |volume=30 |issue=1 |pages=14–7 |date=Spring 2007 |url=http://www.cato.org/pubs/regulation/regv30n1/v30n1-5.pdf |url-status=dead |archive-url=https://web.archive.org/web/20090116012647/http://www.cato.org/pubs/regulation/regv30n1/v30n1-5.pdf |archive-date=2009-01-16 }}

Steven Milloy, the "junk science" commentator for Fox News and a former Philip Morris consultant,[https://ssl.tnr.com/p/docsub.mhtml?i=20060206&s=thacker020606 Smoked Out: Pundit for Hire], by Paul D. Thacker. Published in The New Republic on January 26, 2006. Retrieved August 22, 2007.[http://legacy.library.ucsf.edu/tid/kwk84a00 Philip Morris budget for "Strategy and Social Responsibility"], listing Milloy as a paid consultant. Retrieved August 22, 2007. claimed that "of the 19 studies" on passive smoking "only 8— slightly more than 42%— reported statistically significant increases in heart disease incidence."[http://www.junksciencearchive.com/news/bmjsmoke.html "Secondhand Joking"], by Steven Milloy. Retrieved May 31, 2013.

Another component of criticism cited by Milloy focused on relative risk and epidemiological practices in studies of passive smoking. Milloy, who has a master's degree from the Johns Hopkins School of Hygiene and Public Health, argued that studies yielding relative risks of less than 2 were meaningless junk science. This approach to epidemiological analysis was criticized in the American Journal of Public Health:

{{blockquote|A major component of the industry attack was the mounting of a campaign to establish a "bar" for "sound science" that could not be fully met by most individual investigations, leaving studies that did not meet the criteria to be dismissed as "junk science."{{cite journal |vauthors=Samet JM, Burke TA |title=Turning Science Into Junk: The Tobacco Industry and Passive Smoking |journal=Am J Public Health |volume=91 |issue=11 |pages=1742–4 |year=2001 |pmid=11684591 |doi=10.2105/AJPH.91.11.1742 |pmc=1446866 }}}}

The tobacco industry and affiliated scientists also put forward a set of "Good Epidemiology Practices" which would have the practical effect of obscuring the link between secondhand smoke and lung cancer; the privately stated goal of these standards was to "impede adverse legislation".[http://www.pmdocs.com/PDF/2029059645_9652_0.PDF Scientific Communications Through the Media]{{dead link|date=March 2018 |bot=InternetArchiveBot |fix-attempted=yes }}, from the Philip Morris document archive. Retrieved October 3, 2007. Also cited in {{cite journal |last1=Ong |first1=Elisa K. |last2=Glantz |first2=Stanton A. |title=Constructing 'Sound Science' and 'Good Epidemiology': Tobacco, Lawyers, and Public Relations Firms |journal=American Journal of Public Health |date=November 2001 |volume=91 |issue=11 |pages=1749–1757 |doi=10.2105/ajph.91.11.1749 |pmid=11684593 |pmc=1446868 }} However, this effort was largely abandoned when it became clear that no independent epidemiological organization would agree to the standards proposed by Philip Morris et al.{{cite journal |vauthors=Ong EK, Glantz SA |title=Constructing "Sound Science" and "Good Epidemiology": Tobacco, Lawyers, and Public Relations Firms |journal=Am J Public Health |volume=91 |issue=11 |pages=1749–57 |year=2001 |pmid=11684593 |doi=10.2105/AJPH.91.11.1749 |pmc=1446868 }}

In 1995, Levois and Layard, both tobacco industry consultants, published two analyses in the journal Regulatory Toxicology and Pharmacology regarding the association between spousal exposure to secondhand smoke and heart disease. Both of these papers reported no association between secondhand smoke and heart disease.{{cite journal |last1=Layard |first1=M.W. |title=Ischemic Heart Disease and Spousal Smoking in the National Mortality Followback Survey |journal=Regulatory Toxicology and Pharmacology |date=February 1995 |volume=21 |issue=1 |pages=180–183 |doi=10.1006/rtph.1995.1022 |pmid=7784629 }}{{cite journal |last1=Levois |first1=M.E. |last2=Layard |first2=M.W. |title=Publication Bias in the Environmental Tobacco Smoke/Coronary Heart Disease Epidemiologic Literature |journal=Regulatory Toxicology and Pharmacology |date=February 1995 |volume=21 |issue=1 |pages=184–191 |doi=10.1006/rtph.1995.1023 |pmid=7784630 }} These analyses have been criticized for failing to distinguish between current and former smokers, despite the fact that former smokers, unlike current ones, are not at a significantly increased risk of heart disease.{{cite journal |last1=Law |first1=Malcolm R |last2=Wald |first2=Nicholas J |title=Environmental tobacco smoke and ischemic heart disease |journal=Progress in Cardiovascular Diseases |date=July 2003 |volume=46 |issue=1 |pages=31–38 |doi=10.1016/s0033-0620(03)00078-1 |pmid=12920699 }}

A 1998 study by the International Agency for Research on Cancer (IARC) on environmental tobacco smoke (ETS) found "weak evidence of a dose–response relationship between risk of lung cancer and exposure to spousal and workplace ETS."{{cite journal |last1=Boffetta |first1=Paolo |last2=Agudo |first2=Antonio |last3=Ahrens |first3=Wolfgang |last4=Benhamou |first4=Ellen |last5=Benhamou |first5=Simone |last6=Darby |first6=Sarah C. |last7=Ferro |first7=Gilles |last8=Fortes |first8=Cristina |last9=Gonzalez |first9=Carlos A. |last10=Jöckel |first10=Karl-Heinz |last11=Krauss |first11=Martin |last12=Kreienbrock |first12=Lothar |last13=Kreuzer |first13=Michaela |last14=Mendes |first14=Anabela |last15=Merletti |first15=Franco |last16=Nyberg |first16=Fredrik |last17=Pershagen |first17=Göran |last18=Pohlabeln |first18=Hermann |last19=Riboli |first19=Elio |last20=Schmid |first20=Giovanni |last21=Simonato |first21=Lorenzo |last22=Tre'daniel |first22=Jean |last23=Whitley |first23=Elise |last24=Wichmann |first24=Heinz-Erich |last25=Winck |first25=Carlos |last26=Zambon |first26=Paola |last27=Saracci |first27=Rodolfo |title=Multicenter Case-Control Study of Exposure to Environmental Tobacco Smoke and Lung Cancer in Europe |journal=JNCI: Journal of the National Cancer Institute |date=7 October 1998 |volume=90 |issue=19 |pages=1440–1450 |doi=10.1093/jnci/90.19.1440 |pmid=9776409 |doi-access=free }}

In March 1998, before the study was published, reports appeared in the media alleging that the IARC and the World Health Organization (WHO) were suppressing information. The reports, appearing in the British Sunday Telegraph{{cite web |title=Passive Smoking Doesn't Cause Cancer —Official |url=http://tobaccodocuments.org/pm/2063594041-4042.html |url-status=dead |archive-url=https://web.archive.org/web/20071013185243/http://tobaccodocuments.org/pm/2063594041-4042.html |archive-date=2007-10-13 }} and The Economist,{{cite web|title=Smokescreens – The World Health Organization is showing signs of allowing politics to get in the way of truth. The Economist March 14th, 1998|url=http://ltdlimages.library.ucsf.edu/imagesv/v/d/m/vdm97d00/Svdm97d00.pdf|url-status=dead|archive-url=https://web.archive.org/web/20071129085456/http://ltdlimages.library.ucsf.edu/imagesv/v/d/m/vdm97d00/Svdm97d00.pdf|archive-date=2007-11-29}} among other sources,Le Grand C. Anti-smokers blown away by study. Australian 1998, March 10.WHO Rejects smoking link with lung cancer. Zimbabwe Independent 1998, Oct 23.No Link Between Passive Smoking and Lung Cancer. The Times 1998, March 9. alleged that the WHO withheld from publication of its own report that supposedly failed to prove an association between passive smoking and a number of other diseases (lung cancer in particular).

In response, the WHO issued a press release stating that the results of the study had been "completely misrepresented" in the popular press and were in fact very much in line with similar studies demonstrating the harms of passive smoking.{{cite journal |title=Passive smoking does cause lung cancer, do not let them fool you |journal=The Ceylon Medical Journal |date=June 1998 |volume=43 |issue=2 |pages=98 |pmid=9704550 }} The study was published in the Journal of the National Cancer Institute in October of the same year, and concluded the authors found "no association between childhood exposure to ETS and lung cancer risk" but "did find weak evidence of a dose–response relationship between risk of lung cancer and exposure to spousal and workplace ETS." An accompanying editorial summarized:

{{blockquote|When all the evidence, including the important new data reported in this issue of the Journal, is assessed, the inescapable scientific conclusion is that ETS is a low-level lung carcinogen.{{cite journal |last1=Blot |first1=William J. |last2=McLaughlin |first2=Joseph K. |title=Passive Smoking and Lung Cancer Risk: What Is the Story Now? |journal=JNCI: Journal of the National Cancer Institute |date=7 October 1998 |volume=90 |issue=19 |pages=1416–1417 |doi=10.1093/jnci/90.19.1416 |pmid=9776401 |doi-access=free }}}}

With the release of formerly classified tobacco industry documents through the Tobacco Master Settlement Agreement, it was found (by Elisa Ong and Stanton Glantz) that the controversy over the WHO's alleged suppression of data had been engineered by Philip Morris, British American Tobacco, and other tobacco companies in an effort to discredit scientific findings which would harm their business interests.{{cite journal |vauthors=Ong EK, Glantz SA |title=Tobacco industry efforts subverting International Agency for Research on Cancer's second-hand smoke study |journal=Lancet |volume=355 |issue=9211 |pages=1253–9 |year=2000 |pmid=10770318 |doi=10.1016/S0140-6736(00)02098-5 |s2cid=25145666 }} A WHO inquiry, conducted after the release of the tobacco-industry documents, found that this controversy was generated by the tobacco industry as part of its larger campaign to cut the WHO's budget, distort the results of scientific studies on passive smoking, and discredit the WHO as an institution. This campaign was carried out using a network of ostensibly independent front organizations and international and scientific experts with hidden financial ties to the industry.{{cite web|title=Tobacco Companies Strategies to Undermine Tobacco Control Activities at the World Health Organization|url=https://www.who.int/tobacco/media/en/who_inquiry.pdf|archive-url=http://webarchive.loc.gov/all/20040821060747/http://www.who.int/tobacco/media/en/who_inquiry.pdf|url-status=dead|archive-date=2004-08-21|access-date=2008-12-30}}

In 1993, the United States Environmental Protection Agency (EPA) issued a report estimating that 3,000 lung cancer related deaths in the United States were caused by passive smoking annually.US Environmental Protection Agency. {{cite web|url= http://oaspub.epa.gov/eims/eimscomm.getfile?p_download_id=36793 |title=Respiratory health effects of passive smoking: Lung cancer and other disorders }}

Philip Morris, R.J. Reynolds Tobacco Company, and groups representing growers, distributors and marketers of tobacco took legal action, claiming that the EPA had manipulated this study and ignored accepted scientific and statistical practices.

The United States District Court for the Middle District of North Carolina ruled in favor of the tobacco industry in 1998, finding that the EPA had failed to follow proper scientific and epidemiologic practices and had "cherry picked" evidence to support conclusions which they had committed to in advance.{{cite web |title=The Osteen Decision |url=http://www.tobacco.org/Documents/980717osteen.html |archive-url=https://web.archive.org/web/20000815224937/http://www.tobacco.org/Documents/980717osteen.html |url-status=dead |archive-date=2000-08-15 }} The court stated in part, "EPA publicly committed to a conclusion before research had begun...adjusted established procedure and scientific norms to validate the Agency's public conclusion... In conducting the ETS Risk Assessment, disregarded information and made findings on selective information; did not disseminate significant epidemiologic information; deviated from its Risk Assessment Guidelines; failed to disclose important findings and reasoning..."

In 2002, the EPA successfully appealed this decision to the United States Court of Appeals for the Fourth Circuit. The EPA's appeal was upheld on the preliminary grounds that their report had no regulatory weight, and the earlier finding was vacated.{{cite web|title=Flue-Cured Tobacco Cooperative vs. EPA|url=http://pacer.ca4.uscourts.gov/opinion.pdf/982407.P.pdf|access-date=2008-12-30|url-status=dead|archive-url=https://web.archive.org/web/20081009020709/http://pacer.ca4.uscourts.gov/opinion.pdf/982407.P.pdf|archive-date=2008-10-09}}

In 1998, the U.S. Department of Health and Human Services, through the publication by its National Toxicology Program of the 9th Report on Carcinogens, listed environmental tobacco smoke among the known carcinogens, observing of the EPA assessment that "The individual studies were carefully summarized and evaluated."{{cite book |contribution=Final Report on Carcinogens – Background Document for Environmental Tobacco Smoke |title=Meeting of the NTP Board of Scientific Counselors – Report on Carcinogens Subcommittee |editor1=U.S. Department of Health |editor2=Human Services |editor3=National Toxicology Program |location=Research Triangle Park, North Carolina |date=December 2–3, 1998 |url=https://ntp.niehs.nih.gov/ntp/newhomeroc/other_background/tobacco_smoking1_2apps_508.pdf |page=24 |archive-url=https://web.archive.org/web/20071129085500/http://ntp.niehs.nih.gov/files/EnvironmentalTS.pdf |archive-date=2007-11-29 }}

The tobacco industry's role in funding scientific research on secondhand smoke has been controversial.{{cite journal |author=Thun MJ |title=Passive smoking: Tobacco industry publishes disinformation |journal=BMJ |volume=327 |issue=7413 |pages=502–3; author reply 504–5 |year=2003 |pmid=12946979 |doi=10.1136/bmj.327.7413.502-c |pmc=188400 }} A review of published studies found that tobacco-industry affiliation was strongly correlated with findings exonerating secondhand smoke; researchers affiliated with the tobacco industry were 88 times more likely than independent researchers to conclude that secondhand smoke was not harmful.{{cite journal |vauthors=Barnes DE, Bero LA |title=Why review articles on the health effects of passive smoking reach different conclusions |journal=JAMA |volume=279 |issue=19 |pages=1566–70 |year=1998 |pmid=9605902|doi=10.1001/jama.279.19.1566 }} In a specific example which came to light with the release of tobacco-industry documents, Philip Morris executives successfully encouraged an author to revise his industry-funded review article to downplay the role of secondhand smoke in sudden infant death syndrome.{{cite journal |vauthors=Tong EK, England L, Glantz SA |title=Changing conclusions on secondhand smoke in a sudden infant death syndrome review funded by the tobacco industry |journal=Pediatrics |volume=115 |issue=3 |pages=e356–66 |year=2005 |pmid=15741361 |doi=10.1542/peds.2004-1922 |s2cid=33226933 |doi-access=free }} The 2006 U.S. Surgeon General's report criticized the tobacco industry's role in the scientific debate:

{{blockquote|The industry has funded or carried out research that has been judged to be biased, supported scientists to generate letters to editors that criticized research publications, attempted to undermine the findings of key studies, assisted in establishing a scientific society with a journal, and attempted to sustain controversy even as the scientific community reached consensus.{{cite web |title = The Health Consequences of Involuntary Exposure to Tobacco Smoke |publisher = Surgeon General of the United States |website = Executive Summary |year = 2006 |access-date =2009-01-28 |url = http://www.surgeongeneral.gov/library/secondhandsmoke/report/executivesummary.pdf |page=21}}}}

This strategy was outlined at an international meeting of tobacco companies in 1988, at which Philip Morris proposed to set up a team of scientists, organized by company lawyers, to "carry out work on ETS to keep the controversy alive."{{cite web |url = http://tobaccodocuments.org/landman/2063791182-1187.html |title = Minutes of a meeting of Philip Morris with British tobacco companies to discuss tobacco-industry strategy on passive smoking |access-date = 2007-08-27 |url-status = dead |archive-url = https://web.archive.org/web/20071013185238/http://tobaccodocuments.org/landman/2063791182-1187.html |archive-date = 2007-10-13 }} All scientific research was subject to oversight and "filtering" by tobacco-industry lawyers:

{{blockquote

|Philip Morris then expect the group of scientists to operate within the confines of decisions taken by PM scientists to determine the general direction of research, which apparently would then be 'filtered' by lawyers to eliminate areas of sensitivity.

}}

Philip Morris reported that it was putting "...vast amounts of funding into these projects... in attempting to coordinate and pay so many scientists on an international basis to keep the ETS controversy alive."

Measures to tackle secondhand smoke pose a serious economic threat to the tobacco industry, having broadened the definition of smoking beyond a personal habit to something with a social impact. In a confidential 1978 report, the tobacco industry described increasing public concerns about secondhand smoke as "the most dangerous development to the viability of the tobacco industry that has yet occurred."[http://legacy.library.ucsf.edu/tid/qra99d00 A Study of Public Attitudes toward Cigarette Smoking and the Tobacco Industry in 1978], produced for the Tobacco Institute and released under the terms of the Tobacco Master Settlement Agreement. In United States of America v. Philip Morris et al., the District Court for the District of Columbia found that the tobacco industry "... recognized from the mid-1970s forward that the health effects of passive smoking posed a profound threat to industry viability and cigarette profits," and that the industry responded with "efforts to undermine and discredit the scientific consensus that ETS causes disease."

Accordingly, the tobacco industry have developed several strategies to minimise the impact on their business:

• The industry has sought to position the secondhand smoke debate as essentially concerned with civil liberties and smokers' rights rather than with health, by funding groups such as FOREST.{{cite journal |last1=Smith |first1=E. A. |last2=Malone |first2=R. E. |title='We will speak as the smoker': the tobacco industry's smokers' rights groups |journal=The European Journal of Public Health |date=5 January 2007 |volume=17 |issue=3 |pages=306–313 |doi=10.1093/eurpub/ckl244 |pmid=17065174 |pmc=2794244 }}
• Funding bias in research; in all reviews of the effects of secondhand smoke on health published between 1980 and 1995, the only factor associated with concluding that secondhand smoke is not harmful was whether an author was affiliated with the tobacco industry. However, not all studies that failed to find evidence of harm were by industry-affiliated authors.
• Delaying and discrediting legitimate research (see for an example of how the industry attempted to discredit Takeshi Hirayama's landmark study, and{{cite journal |vauthors=Trotter L, Chapman S |title="Conclusions about exposure to ETS and health that will be unhelpful to us"*: How the tobacco industry attempted to delay and discredit the 1997 Australian National Health and Medical Research Council report on passive smoking |journal=Tob Control |volume=12 |issue=Suppl 3:iii |pages=102–6 |year=2003 |pmid=14645955 |doi=10.1136/tc.12.suppl_3.iii102 |pmc=1766130 }} for an example of how it attempted to delay and discredit a major Australian report on passive smoking)
• Promoting "good epidemiology" and attacking so-called junk science (a term popularised by industry lobbyist Steven Milloy): attacking the methodology behind research showing health risks as flawed and attempting to promote sound science. Ong & Glantz (2001) cite an internal Phillip Morris memo giving evidence of this as company policy.
• Creation of outlets for favourable research. In 1989, the tobacco industry established the International Society of the Built Environment, which published the peer-reviewed journal Indoor and Built Environment. This journal did not require conflict-of-interest disclosures from its authors. With documents made available through the Master Settlement, it was found that the executive board of the society and the editorial board of the journal were dominated by paid tobacco-industry consultants. The journal published a large amount of material on passive smoking, much of which was "industry-positive".{{cite journal |vauthors=Garne D, Watson M, Chapman S, Byrne F |title=Environmental tobacco smoke research published in the journal Indoor and Built Environment and associations with the tobacco industry |journal=Lancet |volume=365 |issue=9461 |pages=804–9 |year=2005 |pmid=15733724 |doi=10.1016/S0140-6736(05)17990-2 |s2cid=23160158 }}

Citing the tobacco industry's production of biased research and efforts to undermine scientific findings, the 2006 U.S. Surgeon General's report concluded that the industry had "attempted to sustain controversy even as the scientific community reached consensus... industry documents indicate that the tobacco industry has engaged in widespread activities... that have gone beyond the bounds of accepted scientific practice." The U.S. District Court, in U.S.A. v. Philip Morris et al., found that "...despite their internal acknowledgment of the hazards of secondhand smoke, Defendants have fraudulently denied that ETS causes disease."{{harvnb|Kessler|2006|p=1523}}

The positions of major tobacco companies on the issue of secondhand smoke is somewhat varied. In general, tobacco companies have continued to focus on questioning the methodology of studies showing that secondhand smoke is harmful. Some (such as British American Tobacco and Philip Morris) acknowledge the medical consensus that secondhand smoke carries health risks, while others continue to assert that the evidence is inconclusive. Several tobacco companies advocate the creation of smoke-free areas within public buildings as an alternative to comprehensive smoke-free laws.The most current positions of major tobacco companies on the issue of passive smoking can be found on their websites. As of 13 January 2009, the following websites contain tobacco-industry positions on the topic:

• British American Tobacco: [http://www.bat.com/group/sites/uk__3mnfen.nsf/vwPagesWebLive/DO52AMJ4]
• Imperial Tobacco: {{cite web |title=Imperial Tobacco Group PLC - Media - Our view - Smoking and health - Environmental tobacco smoke |url=http://www.imperial-tobacco.com/index.asp?page=82 |url-status=dead |archive-url=https://web.archive.org/web/20090116015146/http://www.imperial-tobacco.com/index.asp?page=82 |archive-date=2009-01-16 |access-date=2008-10-25}}
• Philip Morris: [http://www.philipmorrisusa.com/en/cms/Products/Cigarettes/Health_Issues/Secondhand_Smoke/default.aspx USA] {{Webarchive|url=https://web.archive.org/web/20101006025905/http://www.philipmorrisusa.com/en/cms/Products/Cigarettes/Health_Issues/Secondhand_Smoke/default.aspx|date=2010-10-06}} and [http://www.philipmorrisinternational.com/PMINTL/pages/eng/smoking/Secondhand_smoke.asp International]
• R. J. Reynolds Tobacco Company: {{cite web |title=R.J. Reynolds Tobacco Company - Smoking & Health - Summary of Opinions |url=http://www.rjrt.com/smoking/summaryCover.asp |url-status=dead |archive-url=https://web.archive.org/web/20061118145334/http://www.rjrt.com/smoking/summaryCover.asp |archive-date=2006-11-18 |access-date=2006-11-19}}

On September 22, 1999, the U.S. Department of Justice filed a racketeering lawsuit against Philip Morris and other major cigarette manufacturers.[http://www.usdoj.gov/civil/cases/tobacco2/index.htm Litigation Against Tobacco Companies] U.S. Department of Justice Almost 7 years later, on August 17, 2006, U.S. District Court Judge Gladys Kessler found that the Government had proven its case and that the tobacco company defendants had violated the Racketeer Influenced Corrupt Organizations Act (RICO). In particular, Judge Kessler found that PM and other tobacco companies had:

• conspired to minimize, distort and confuse the public about the health hazards of smoking;
• publicly denied, while internally acknowledging, that secondhand tobacco smoke is harmful to nonsmokers, and
• destroyed documents relevant to litigation.

The ruling found that tobacco companies undertook joint efforts to undermine and discredit the scientific consensus that secondhand smoke causes disease, notably by controlling research findings via paid consultants. The ruling also concluded that tobacco companies were fraudulently continuing to deny the health effects of ETS exposure.

On May 22, 2009, a three-judge panel of the U.S. Court of Appeals for the District of Columbia Circuit unanimously upheld the lower court's 2006 ruling.[http://pacer.cadc.uscourts.gov/common/opinions/200905/06-5267-1181914.pdf Appeal Ruling], U.S. Court of Appeals for the District of Columbia Circuit, 22 May 2009[https://www.bloomberg.com/apps/news?pid=newsarchive&sid=aTHJN4mM4M3I Altria, Cigarette Makers Lose 'Lights' Ruling Appeal] Bloomberg news, 22 May 2009[https://www.reuters.com/article/domesticNews/idUSTRE54L44820090522?pageNumber=2&virtualBrandChannel=10531&sp=true U.S. appeals court agrees tobacco companies lied] Reuters, 22 May 2009

{{See also|Smoking ban|List of smoking bans|Smoking bans in private vehicles}}

As a consequence of the health risks associated with secondhand smoke, many national and local governments have outlawed smoking in indoor public places, including restaurants, cafés, and nightclubs, as well as some outdoor open areas.[http://gothamist.com/2011/05/18/smokers_just_daring_bloomberg_to_ti.php Smokers Daring Bloomberg To Ticket Them Under Park Ban] {{webarchive|url=https://web.archive.org/web/20131126094031/http://gothamist.com/2011/05/18/smokers_just_daring_bloomberg_to_ti.php |date=2013-11-26 }} Ireland was the first country in the world to institute a comprehensive national ban on smoking in all indoor workplaces on 29 March 2004. Since then, many others have followed suit. The countries which have ratified the WHO Framework Convention on Tobacco Control (FCTC) have a legal obligation to implement effective legislation "for protection from exposure to tobacco smoke in indoor workplaces, public transport, indoor public places and, as appropriate, other public places." (Article 8 of the FCTC{{cite web |url = http://whqlibdoc.who.int/publications/2003/9241591013.pdf |title = WHO Framework Convention on Tobacco Control |publisher = World Health Organization |quote = Parties recognize that scientific evidence has unequivocally established that exposure to tobacco causes death, disease and disability |date = 2005-02-27 |access-date = 2009-01-12 }}) The parties to the FCTC have further adopted Guidelines on the Protection from Exposure to secondhand Smoke which state that "effective measures to provide protection from exposure to tobacco smoke ... require the total elimination of smoking and tobacco smoke in a particular space or environment in order to create a 100% smoke-free environment."{{cite web |title = Guidelines on the Protection from Exposure to Secondhand Smoke |website = Framework Convention on Tobacco Control |publisher = World Health Organization |year = 2007 |access-date =2009-01-29 |url =https://www.who.int/fctc/cop/art%208%20guidelines_english.pdf }}

Opinion polls have shown considerable support for smoke-free laws. In June 2007, a survey of 15 countries found 80% approval for such laws.[http://www.marketresearchworld.net/index.php?option=content&task=view&id=1619&Itemid= Market Research World] A survey in France, reputedly a nation of smokers, showed 70% support.

Smoking bans by governments result in decreased harm from secondhand smoke, including less admissions for acute coronary syndrome.{{cite journal |last1=Frazer |first1=Kate |last2=Callinan |first2=Joanne E |last3=McHugh |first3=Jack |last4=van Baarsel |first4=Susan |last5=Clarke |first5=Anna |last6=Doherty |first6=Kirsten |last7=Kelleher |first7=Cecily |title=Legislative smoking bans for reducing harms from secondhand smoke exposure, smoking prevalence and tobacco consumption |journal=Cochrane Database of Systematic Reviews |date=4 February 2016 |volume=2016 |issue=2 |pages=CD005992 |doi=10.1002/14651858.CD005992.pub3 |pmid=26842828 |pmc=6486282 }} In the first 18 months after the town of Pueblo, Colorado, enacted a smoke-free law in 2003, hospital admissions for heart attacks dropped 27%. Admissions in neighbouring towns without smoke-free laws showed no change, and the decline in heart attacks in Pueblo was attributed to the resulting reduction in secondhand smoke exposure.{{cite journal |title=Reduced hospitalizations for acute myocardial infarction after implementation of a smoke-free ordinance—City of Pueblo, Colorado, 2002–2006 |journal=MMWR Morb. Mortal. Wkly. Rep. |volume=57 |issue=51 |pages=1373–7 |date=January 2009 |pmid=19116606 |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5751a1.htm |author1= Centers for Disease Control and Prevention (CDC) }} A 2004 smoking ban instituted in Massachusetts workplaces decreased workers' secondhand smoke exposure from 8% of workers in 2003 to 5.4% of workers in 2010.{{cite web |url = http://blogs.cdc.gov/niosh-science-blog/2013/11/21/ets/ |title = Reducing Worker Exposure to ETS |publisher = National Institute for Occupational Safety and Health (NIOSH) |date = 21 November 2013 |last = Fitzsimmons |first = Kathleen |access-date = 14 January 2015}} A 2016 review also found that bans and policy changes in specific locations such as hospitals or universities can lead to reduced smoking rates. In prison settings bans might lead to reduced mortality and to lower exposure to secondhand smoke.{{cite journal |last1=Frazer |first1=Kate |last2=McHugh |first2=Jack |last3=Callinan |first3=Joanne E |last4=Kelleher |first4=Cecily |title=Impact of institutional smoking bans on reducing harms and secondhand smoke exposure |journal=Cochrane Database of Systematic Reviews |date=27 May 2016 |volume=2016 |issue=5 |pages=CD011856 |doi=10.1002/14651858.CD011856.pub2 |pmid=27230795 |pmc=10164285 }}

In 2001, a systematic review for the Guide to Community Preventive Services acknowledged strong evidence of the effectiveness of smoke-free policies and restrictions in reducing expose to secondhand smoke. A follow-up to this review, identified the evidence on which the effectiveness of smoking bans reduced the prevalence of tobacco use. Articles published until 2005, were examined to further support this evidence. The examined studies provided sufficient evidence that smoke-free policies reduce tobacco use among workers when implemented in worksites or by communities.{{cite journal | vauthors = Hopkins DP, Razi S, Leeks KD, Priya Kalra G, Chattopadhyay SK, Soler RE | year = 2010 | title = Smokefree policies to reduce tobacco use. A systematic review | journal = Am J Prev Med | volume = 38 | issue = 2 Suppl | pages = S275–89 | doi = 10.1016/j.amepre.2009.10.029 | pmid = 20117612| author7 = Task Force on Community Preventive Services }}

While a number of studies funded by the tobacco industry have claimed a negative economic impact from smoke-free laws, no independently funded research has shown any such impact. A 2003 review reported that independently funded, methodologically sound research consistently found either no economic impact or a positive impact from smoke-free laws.{{cite journal |vauthors=Scollo M, Lal A, Hyland A, Glantz S |title=Review of the quality of studies on the economic effects of smoke-free policies on the hospitality industry |journal=Tobacco Control |date=Mar 2003 |pmid=12612356 |pmc=1759095 |volume=12 |issue=1 |pages=13–20 |doi=10.1136/tc.12.1.13}}

Air nicotine levels were measured in Guatemalan bars and restaurants before and after an implemented smoke-free law in 2009. Nicotine concentrations significantly decreased in both the bars and restaurants measured. Also, the employees' support for a smoke-free workplace substantially increased in the post-implementation survey compared to pre-implementation survey.{{cite journal |vauthors=Barnoya J, Arvizu M, Jones MR, Hernandez JC, Breysse PN, Navas-Acien A |title=Secondhand smoke exposure in bars and restaurants in Guatemala City: before and after smoking ban evaluation |journal=Cancer Causes Control |volume=22 |issue=1 |pages=151–6 |date=November 2010 |pmid=21046446 |doi=10.1007/s10552-010-9673-8 |s2cid=673901 }}

Recent surveys taken by the Society for Research on Nicotine and Tobacco demonstrate supportive attitudes of the public towards smoke-free policies in outdoor areas. A vast majority of the public supports restricting smoking in various outdoor settings. The respondents' support for the policies were for varying reasons such as litter control, establishing positive smoke-free role models for youth, reducing youth opportunities to smoke, and avoiding exposure to secondhand smoke.{{cite journal |last1=Thomson |first1=George |last2=Wilson |first2=Nick |last3=Edwards |first3=Richard |title=At the frontier of tobacco control: A brief review of public attitudes toward smoke-free outdoor places |journal=Nicotine & Tobacco Research |date=June 2009 |volume=11 |issue=6 |pages=584–590 |doi=10.1093/ntr/ntp046 |pmid=19359392 |doi-access=free }}

Alternatives to smoke-free laws have also been proposed as a means of harm reduction, particularly in bars and restaurants. For example, critics of smoke-free laws cite studies suggesting ventilation as a means of reducing tobacco smoke pollutants and improving air quality.{{cite news |title=No ifs or butts |url=https://www.building.co.uk/no-ifs-or-butts/3047478.article |work=Building |date=7 March 2005 }} Ventilation has also been heavily promoted by the tobacco industry as an alternative to outright bans, via a network of ostensibly independent experts with often undisclosed ties to the industry.{{cite journal |vauthors=Drope J, Bialous SA, Glantz SA |title=Tobacco industry efforts to present ventilation as an alternative to smoke-free environments in North America |journal=Tob Control |volume=13 |issue=Suppl 1 |pages=i41–7 |date=March 2004 |pmid=14985616 |pmc=1766145 |doi= 10.1136/tc.2003.004101|quote = The industry developed a network of ventilation 'experts' to promote its position that smoke-free environments were not necessary, often without disclosing the financial relationship between these experts and the industry. }} However, not all critics have connections to the industry.

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) officially concluded in 2005 that while completely isolated smoking rooms do eliminate the risk to nearby non-smoking areas, smoking bans are the only means of eliminating health risks associated with indoor exposure. They further concluded that no system of dilution or cleaning was effective at eliminating risk.{{cite web |title=ASHRAE Position Document on Environmental Tobacco Smoke |url=https://www.ashrae.org/file%20library/about/position%20documents/pd_environmental-tobacco-smoke-2020-07-1.pdf |publisher=American Society of Heating, Refrigerating and Air-Conditioning Engineers |date=July 2020 }} The U.S. Surgeon General and the European Commission Joint Research Centre have reached similar conclusions.{{cite web |title = The Health Consequences of Involuntary Exposure to Tobacco Smoke |publisher = Surgeon General of the United States |website = Executive Summary |year = 2006 |access-date =2009-01-28 |url = http://www.surgeongeneral.gov/library/secondhandsmoke/report/executivesummary.pdf }}{{cite web|publisher=European Commission Joint Research Centre |title=Institute for Health and Consumer Protection Activity Report 2003 |year=2003 |url=http://ihcp.jrc.ec.europa.eu/docs/IHCP_annual_report/ihcp03.pdf |access-date=2009-01-28 |url-status=dead |archive-url=https://web.archive.org/web/20090327101821/http://ihcp.jrc.ec.europa.eu/docs/IHCP_annual_report/ihcp03.pdf |archive-date=March 27, 2009 }} The implementation guidelines for the WHO Framework Convention on Tobacco Control states that engineering approaches, such as ventilation, are ineffective and do not protect against secondhand smoke exposure. However, this does not necessarily mean that such measures are useless in reducing harm, only that they fall short of the goal of reducing exposure completely to zero.

Others have suggested a system of tradable smoking pollution permits, similar to the cap-and-trade pollution permits systems used by the United States Environmental Protection Agency in recent decades to curb other types of pollution.{{cite news |title = Let Bars Buy, Sell Smoking Permits |url = http://www.madison.com/archives/read.php?ref=/madison.com/html/archive_files/wsj/2005/09/25/0509240280.php |first = Robert |last = Haveman |author2 = John Mullahy |work = Wisconsin State Journal |date = September 25, 2005 |access-date = 2009-01-28 |page = B2 |url-status = dead |archive-url = https://web.archive.org/web/20090104145317/http://www.madison.com/archives/read.php?ref=%2Fmadison.com%2Fhtml%2Farchive_files%2Fwsj%2F2005%2F09%2F25%2F0509240280.php |archive-date = January 4, 2009 }} This would guarantee that a portion of bars/restaurants in a jurisdiction will be smoke-free, while leaving the decision to the market.

{{main|Animals and tobacco smoke}}

Multiple studies have been conducted to determine the carcinogenicity of environmental tobacco smoke to animals. These studies typically fall under the categories of simulated environmental tobacco smoke, administering condensates of sidestream smoke, or observational studies of cancer among pets.

To simulate environmental tobacco smoke, scientists expose animals to sidestream smoke, that which emanates from the cigarette's burning cone and through its paper, or a combination of mainstream and sidestream smoke. The IARC monographs conclude that mice with prolonged exposure to simulated environmental tobacco smoke, that is six hours a day, five days a week, for five months with a subsequent four-month interval before dissection, will have significantly higher incidence and multiplicity of lung tumors than with control groups.

The IARC monographs concluded that sidestream smoke condensates had a significantly higher carcinogenic effect on mice than did mainstream smoke condensates.

Secondhand smoke is popularly recognised as a risk factor for cancer in pets.{{cite web |url = http://www.livescience.com/animals/070831_pets_smoking.html |title = Secondhand Smoke Causes Cancer in Pets |first = Andrea |last = Thompson |publisher = LiveScience |date = 2007-08-31 |access-date = 2007-08-31}} A study conducted by the Tufts University School of Veterinary Medicine and the University of Massachusetts Amherst linked the occurrence of feline oral cancer to exposure to environmental tobacco smoke through an overexpression of the p53 gene.{{cite journal |vauthors=Snyder LA, Bertone ER, Jakowski RM, Dooner MS, Jennings-Ritchie J, Moore AS |title=p53 expression and environmental tobacco smoke exposure in feline oral squamous cell carcinoma |journal=Vet Pathol |volume=41 |issue=3 |pages=209–14 |year=2004 |pmid=15133168 |doi=10.1354/vp.41-3-209 |s2cid=24749614 |doi-access=free }} Another study conducted at the same universities concluded that cats living with a smoker were more likely to get feline lymphoma; the risk increased with the duration of exposure to secondhand smoke and the number of smokers in the household.{{cite journal |vauthors= Bertone ER, Snyder LA, Moore AS |title= Environmental Tobacco Smoke and Risk of Malignant Lymphoma in Pet Cats |journal=American Journal of Epidemiology |volume=156 |issue=3 |pages=268–273 |year=2002 |pmid=12142262 |doi= 10.1093/aje/kwf044 |doi-access=free }} A study by Colorado State University researchers, looking at cases of canine lung cancer, was generally inconclusive, though the authors reported a weak relation for lung cancer in dogs exposed to environmental tobacco smoke. The number of smokers within the home, the number of packs smoked in the home per day, and the amount of time that the dog spent within the home had no effect on the dog's risk for lung cancer.{{cite journal |vauthors=Reif JS, Dunn K, Ogilvie GK, Harris CK |title=Passive smoking and canine lung cancer risk |journal=Am J Epidemiol |volume=135 |issue=3 |pages=234–9 |year=1992 |pmid=1546698 |doi=10.1093/oxfordjournals.aje.a116276}}

• Health effects of tobacco
• Third-hand smoke
• Tobacco control
• Philip Morris v. Uruguay

{{Reflist|colwidth=30em}}

;Scientific bodies

{{Refbegin}}

• [https://web.archive.org/web/20070905172350/http://cancercontrol.cancer.gov/tcrb/monographs/10/index.html Health Effects of Exposure to Environmental Tobacco Smoke], from the U.S. National Cancer Institute
• {{cite web |url= https://ntp.niehs.nih.gov/ntp/roc/content/profiles/tobaccorelatedexposures.pdf |title= Environmental Tobacco Smoke |url-status= live |archive-url= https://web.archive.org/web/20080716173310/http://ntp.niehs.nih.gov/ntp/roc/eleventh/profiles/s176toba.pdf |archive-date= 2008-07-16 }} {{small|(219 KB)}}. From the 11th Report on Carcinogens of the U.S. National Institutes of Health
• {{cite journal |author1=U.S. Dept. of Health and Human Services |author2=Centers for Disease Control and Prevention |author3=Coordinating Center for Health Promotion |author4=National Center for Chronic Disease Prevention and Health Promotion |author5=Office on Smoking and Health |url=https://www.ncbi.nlm.nih.gov/books/NBK44324/ |title=The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General |series=Publications and Reports of the Surgeon General |publisher=Surgeon General of the United States |date=2006-06-27 |location=Atlanta, Ga. |pmid=20669524 |id=O2NLM: WA 754 H4325 2006|ref=CITEREFSurgeon_General2006 |quote=Secondhand smoke exposure causes disease and premature death in children and adults who do not smoke}}
• {{cite book |author1=World Health Organization |author2=International Agency for Research on Cancer |title=Tobacco Smoke and Involuntary Smoking |publisher=IARC Working Group on the Evaluation of Carcinogenic Risks to Humans

|location=Lyon, France |year=2004 |isbn=978-92-832-1283-6 |url=http://monographs.iarc.fr/ENG/Monographs/vol83/mono83.pdf |volume=83 |series=IARC monographs on the evaluation of carcinogenic risks to humans |ref=CITEREFIARC2004|author-link1=World Health Organization |author-link2=International Agency for Research on Cancer }}

• [https://www.cdc.gov/tobacco/data_statistics/fact_sheets/secondhand_smoke/general_facts/ Secondhand Smoke Fact Sheet] from the U.S. Centers for Disease Control and Prevention
• [https://www.cdc.gov/niosh/topics/tobacco/ Tobacco Smoke in the Workplace] from the U.S. Centers for Disease Control and Prevention
• [http://www.oehha.ca.gov/air/environmental_tobacco/2005etsfinal.html Health Effects of Exposure to Environmental Tobacco Smoke], from the California Environmental Protection Agency
• [https://purl.fdlp.gov/GPO/gpo45024 Environmental Tobacco Smoke Exposure in Children Aged 3-19 Years with and Without Asthma in the United States, 1999-2010] National Center for Health Statistics
• {{cite journal |last1=Öberg |first1=Mattias |last2=Jaakkola |first2=Maritta S |last3=Woodward |first3=Alistair |last4=Peruga |first4=Armando |last5=Prüss-Ustün |first5=Annette |title=Worldwide burden of disease from exposure to second-hand smoke: a retrospective analysis of data from 192 countries |journal=The Lancet |date=January 2011 |volume=377 |issue=9760 |pages=139–146 |doi=10.1016/S0140-6736(10)61388-8 |pmid=21112082 |s2cid=7179156 }}

{{Refend}}

;Tobacco industry

{{Refbegin}}

• {{cite web |url=https://www.who.int/tobacco/media/en/who_inquiry.pdf |archive-url=http://webarchive.loc.gov/all/20040821060747/http://www.who.int/tobacco/media/en/who_inquiry.pdf |url-status=dead |archive-date=August 21, 2004 |title=Tobacco Company Strategies to Undermine Tobacco Control Activities |access-date=October 5, 2020 }} {{small|(1.55 MB)}}: Report of the Committee of Experts on Tobacco Industry Documents from the World Health Organization
• [http://legacy.library.ucsf.edu/ The Legacy Tobacco Documents Library] and [http://bat.library.ucsf.edu British American Tobacco Documents Archive] from the University of California, San Francisco
• [http://www.pmdocs.com/ Philip Morris USA Document Archive], made public as a result of the Tobacco Master Settlement Agreement

{{Refend}}

;Other links

{{Refbegin}}

• [https://www.who.int/fctc/cop/art%208%20guidelines_english.pdf Guidelines Protection from Exposure to Secondhand Smoke], by WHO Framework Convention on Tobacco Control
• [http://webarchive.loc.gov/all/20070619093702/http://www.who.int/tobacco/resources/publications/wntd/2007/pol_recommendations/en/index.html WHO Policy recommendations on protection from exposure to second-hand tobacco smoke]
• {{cite journal |last1=Small |first1=Elysia |last2=Shah |first2=Hina P. |last3=Davenport |first3=Jake J. |last4=Geier |first4=Jacqueline E. |last5=Yavarovich |first5=Kate R. |last6=Yamada |first6=Hidetaka |last7=Sabarinath |first7=Sreedharan N. |last8=Derendorf |first8=Hartmut |last9=Pauly |first9=James R. |last10=Gold |first10=Mark S. |last11=Bruijnzeel |first11=Adrie W. |title=Tobacco smoke exposure induces nicotine dependence in rats |journal=Psychopharmacology |date=January 2010 |volume=208 |issue=1 |pages=143–158 |doi=10.1007/s00213-009-1716-z |pmid=19936715 |pmc=3586198 }}
• {{cite web |url=http://publichealthlawcenter.org/sites/default/files/resources/doj-final-opinion.pdf |title=United States of America v. Philip Morris et al.: Final Opinion of Judge Gladys Kessler |publisher=United States District Court for the District of Columbia |last=Kessler |first=Gladys |date=August 17, 2006 }}
• [https://web.archive.org/web/20100821222220/http://www.time.com/time/health/article/0%2C8599%2C2012103%2C00.html "How Secondhand Cigarette Smoke Changes Your Genes"]

{{Refend}}

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