moisturizer

In the human body, water constantly evaporates from the deeper layers of the skin through an effect known as transepidermal water loss. By regulating its water content, human skin naturally maintains a dry, easily shed surface as a barrier against pathogens, dirt, or damage, while protecting itself from drying out and becoming brittle and rigid. The ability to retain moisture depends on the lipid bilayer between the dead skin cells.{{citation | editor=Arza Seidel|display-editors=etal| title=Kirk-Othmer Chemical Technology of Cosmetics | year=2013}}

Moisturizers modify the rate of water loss, with active ingredients of moisturizers falling into one of two categories: occlusives and humectants.{{cite web |last1=Duffill |first1=Mark |last2=Oakley |first2=Amanda |title=Emollients and moisturisers |url=https://dermnetnz.org/topics/emollients-and-moisturisers/ |website=dermnetnz.org |access-date=31 December 2020 |archive-date=25 August 2023 |archive-url=https://web.archive.org/web/20230825045713/https://dermnetnz.org/topics/emollients-and-moisturisers |url-status=live }}

Occlusives form a hydrophobic coating on the surface of the skin, keeping moisture from escaping. The more occlusive the formulation, the greater the effect. Ointments are more occlusive than aqueous creams, which are more occlusive than lotion. Water loss through the skin is normally about 4–8 g/(m²⋅h). A layer of petrolatum applied to normal skin can reduce that loss by 50–75% for several hours. Oils naturally produced by the human body moisturize through this same mechanism.

Humectants are hydrophilic and absorb water. They absorb water from humid air (when >70% humidity) to moisturize the skin. More commonly, however, they draw out water from the dermis into the epidermis, making deeper skin dryer.{{cite journal |last1=Harwood |first1=Anne |last2=Nassereddin |first2=Ali |last3=Krishnamurthy |first3=Karthik |title=Moisturizers |url=https://www.ncbi.nlm.nih.gov/books/NBK545171/ |website=StatPearls |publisher=StatPearls Publishing |access-date=31 December 2020 |date=2020 |pmid=31424755 |archive-date=28 January 2023 |archive-url=https://web.archive.org/web/20230128195629/https://www.ncbi.nlm.nih.gov/books/NBK545171/ |url-status=live }} When used in practical applications, humectants are combined with occlusives.{{cite web |last1=Publishing |first1=Harvard Health |title=Moisturizers: Do they work? |url=https://www.health.harvard.edu/staying-healthy/moisturizers-do-they-work |website=Harvard Health |date=February 2008 |access-date=31 December 2020 |archive-date=20 September 2023 |archive-url=https://web.archive.org/web/20230920001311/https://www.health.harvard.edu/staying-healthy/moisturizers-do-they-work |url-status=live }} Moisturizers commonly contain water, which acts as a temporary hydration agent.

There are many different types of moisturizers. Petrolatum is one of the most effective moisturizers, although it can be unpopular due to its oily consistency.{{cite journal |last1=Sethi |first1=Anisha |last2=Kaur |first2=Tejinder |last3=Malhotra |first3=SK |last4=Gambhir |first4=ML |title=Moisturizers: The Slippery Road |journal=Indian Journal of Dermatology |date=2016 |volume=61 |issue=3 |pages=279–287 |doi=10.4103/0019-5154.182427 |pmid=27293248 |pmc=4885180 |issn=0019-5154|doi-access=free }}{{cite web |last1=Publishing |first1=Harvard Health |title=Choosing a good moisturizer for your skin |url=https://www.health.harvard.edu/staying-healthy/choosing-a-good-moisturizer-for-your-skin |website=Harvard Health |date=5 April 2018 |access-date=31 December 2020 |archive-date=1 October 2023 |archive-url=https://web.archive.org/web/20231001100959/https://www.health.harvard.edu/staying-healthy/choosing-a-good-moisturizer-for-your-skin |url-status=live }}

Other popular moisturizers are cetyl alcohol, cetearyl alcohol, cocoa butter, isopropyl myristate, isopropyl palmitate, lanolin, liquid paraffin, polyethylene glycols, shea butter, silicone oils, stearic acid, stearyl alcohol and castor oil, and other oils.

Moisturizers may also be available as lotions, creams, ointments, bath oils, or soap substitutes.

Mineral oils and waxes are not prone to oxidation or rancidity.{{cite journal |last1=Chuberre |first1=B. |last2=Araviiskaia |first2=E. |last3=Bieber |first3=T. |last4=Barbaud |first4=A. |title=Mineral oils and waxes in cosmetics: an overview mainly based on the current European regulations and the safety profile of these compounds |journal=Journal of the European Academy of Dermatology and Venereology|pages=5–14 |doi=10.1111/jdv.15946 |date=November 2019|volume=33 |issue=Suppl 7 |pmid=31588613 |s2cid=203850745 |doi-access=free }} For this reason, they have essentially replaced vegetable oils in emollients and topical medication.

Moisturizer cosmetics may additionally contain antioxidants, ceramides, emulsifiers, fragrances, penetration enhancers, preservatives, and solvents. Some products are marketed as having anti-wrinkle and skin enhancement effects. Many plant and animal extracts have been claimed to impart skin benefits, but such claims are presented with little scientific evidence.

Moisturizers are used for the treatment of certain skin diseases, such as psoriasis, ichthyosis vulgaris, xerosis, and pruritus in atopic dermatitis. More often, they are bases or vehicles for topical medication, such as in Whitfield's ointment. They are often combined with humectants, such as salicylic acid and urea.{{citation | editor=Tony Burns|display-editors=etal| title=Rook's Textbook of Dermatology | edition=8th | year=2010}}

Moisturizers are also widely used in sunscreens, antiperspirants, skin cleansers, shaving creams, aftershaves, and hair tonics.

Moisturizers are used in disposable diapers to prevent dry skin and diaper dermatitis.

Moisturizers show some beneficial effects in treating atopic dermatitis (eczema). Using moisturizers helps to improve skin comfort and may reduce disease flares.{{cite journal |vauthors=Ridd MJ, Roberts A, Grindlay D, Williams HC |date=October 2019 |title=Which emollients are effective and acceptable for eczema in children? |url=https://research-information.bris.ac.uk/ws/files/219950607/bmj.l5882.full.pdf |url-status=live |journal=BMJ |volume=367 |pages=l5882 |doi=10.1136/bmj.l5882 |pmid=31649114 |s2cid=204882682 |archive-url=https://web.archive.org/web/20230411114201/https://research-information.bris.ac.uk/ws/files/219950607/bmj.l5882.full.pdf |archive-date=2023-04-11 |access-date=2023-04-11}}{{Cite journal|last1=van Zuuren|first1=Esther J|last2=Fedorowicz|first2=Zbys|last3=Christensen|first3=Robin|last4=Lavrijsen|first4=Adriana PM|last5=Arents|first5=Bernd WM|date=2017-02-06|title=Emollients and moisturisers for eczema|journal=Cochrane Database of Systematic Reviews|type=Review|volume=2|issue=8|pages=CD012119|doi=10.1002/14651858.cd012119.pub2|pmid=28166390|issn=1465-1858|pmc=6464068}} They can be used as leave-on treatments, bath additives, or soap substitutes. There are many different moisturizer products, but the majority of leave-on treatments (from least to most greasy) are one of the following: lotions, creams, gels, or ointments. As none of the different types of moisturizers are more effective than the others, people with atopic dermatitis need to choose one or more products according to their age, affected body site, climate/season, and personal preference.{{cite journal |display-authors=6 |vauthors=Ridd MJ, Santer M, MacNeill SJ, Sanderson E, Wells S, Webb D, Banks J, Sutton E, Roberts A, Liddiard L, Wilkins Z, Clayton J, Garfield K, Barrett TJ, Lane JA, Baxter H, Howells L, Taylor J, Hay AD, Williams HC, Thomas KS |date=August 2022 |title=Effectiveness and safety of lotion, cream, gel, and ointment emollients for childhood eczema: a pragmatic, randomised, phase 4, superiority trial |journal=The Lancet. Child & Adolescent Health |volume=6 |issue=8 |pages=522–532 |doi=10.1016/S2352-4642(22)00146-8 |pmid=35617974 |s2cid=249024141 |doi-access=free |hdl-access=free |hdl=1983/e4009d3c-127f-4aa9-bf71-e40401b33eee}} However using moisturizers daily in infants during the first year of life does not help to prevent the development of atopic dermatitis, and might even increase the risk of skin infections.{{Cite report |url=https://evidence.nihr.ac.uk/collection/eczema-in-children-uncertainties-addressed/ |title=Eczema in children: uncertainties addressed |date=2024-03-19 |publisher=NIHR Evidence |doi=10.3310/nihrevidence_62438 |language=en|url-access=subscription }}{{cite journal |vauthors=Kelleher MM, Phillips R, Brown SJ, Cro S, Cornelius V, Carlsen KC, Skjerven HO, Rehbinder EM, Lowe AJ, Dissanayake E, Shimojo N, Yonezawa K, Ohya Y, Yamamoto-Hanada K, Morita K, Axon E, Cork M, Cooke A, Van Vogt E, Schmitt J, Weidinger S, McClanahan D, Simpson E, Duley L, Askie LM, Williams HC, Boyle RJ |date=November 2022 |title=Skin care interventions in infants for preventing eczema and food allergy |journal=The Cochrane Database of Systematic Reviews |volume=2022 |issue=11 |pages=CD013534 |doi=10.1002/14651858.CD013534.pub3 |pmc=9661877 |pmid=36373988 |collaboration=Cochrane Skin Group}}

Persistent moisturization to the skin via water contact may contribute to an allergic reaction or contact dermatitis.{{Citation needed|date=March 2024|reason=This is a scientific/medical claim and must be supported by literature.}} This could allow foreign objects to penetrate the skin.{{Ambiguous|date=March 2024|reason=Is (how) this related to preceding statement? Also, citation would be useful.}}

Changes in the skin's normal ecological environment–either atop or within the skin–can also allow for the overgrowth of pathogens.{{Cite journal|last=Marino|first=Christina|date=2006|title=Skin Physiology, Irritants, Dry Skin and Moisturizers|url=http://www.lni.wa.gov/Safety/Research/Dermatitis/files/skin_phys.pdf|journal=Skin Physiology, Irritants, Dry Skin and Moisturizers|access-date=2019-01-29|archive-date=2017-08-29|archive-url=https://web.archive.org/web/20170829154832/http://www.lni.wa.gov/Safety/Research/Dermatitis/files/skin_phys.pdf|url-status=dead}}

Aromas or food additives in moisturizers may trigger an immune reaction, including development of an allergy.

There is currently no regulation over use of the term "hypoallergenic". In fact, some pediatric skin products marketed as hypoallergenic contained allergens.{{cite web|last1=Parsons|first1=Julia|title=Protect children's skin from unregulated term 'hypoallergenic'|url=https://www.bcm.edu/news/skin-and-hair/protect-kids-from-unregulated-hypoallergenic|website=BAYLOR COLLEGE OF MEDICINE NEWS|access-date=31 December 2015|archive-date=4 March 2016|archive-url=https://web.archive.org/web/20160304073736/https://www.bcm.edu/news/skin-and-hair/protect-kids-from-unregulated-hypoallergenic|url-status=live}}{{cite journal|last1=Schlichte|first1=Megan J.|last2=Katta|first2=Rajani|title=Methylisothiazolinone: An Emergent Allergen in Common Pediatric Skin Care Products|journal=Dermatology Research and Practice|volume=2014|pages=1–4|doi=10.1155/2014/132564|pmid=25342949|pmc=4197884|year=2014|doi-access=free}}

Those with eczema are especially vulnerable to allergic reaction with lotions and creams, as their compromised skin barrier allows preservatives to bind with and activate immune cells.{{cite news|last1=Doyle|first1=Kathryn|title=Some skin creams bad news for eczema|url=https://www.reuters.com/article/us-skin-creams-eczema-idUSBRE9BB14720131212|newspaper=Reuters|access-date=31 December 2015|date=2013-12-12|archive-date=2016-09-24|archive-url=https://web.archive.org/web/20160924101858/http://www.reuters.com/article/us-skin-creams-eczema-idUSBRE9BB14720131212?|url-status=live}}

The American Academy of Allergy, Asthma, and Immunology released a warning in 2014 that natural lotion containing ingredients commonly found in food (such as goats milk, cow's milk, coconut milk, or oil) may introduce new allergies, potentially causing an allergic reaction upon later consuming such foods.{{cite web|last1=Graham|first1=Melissa|title=Researchers find link between natural lotions, new food allergies|url=http://www.aaaai.org/about-the-aaaai/newsroom/news-releases/natural-lotions.aspx|website=American Academy of Allergy, Asthma & Immunology|access-date=31 December 2015|archive-url=https://web.archive.org/web/20171109191313/http://www.aaaai.org/about-aaaai/newsroom/news-releases/natural-lotions|archive-date=2017-11-09}} A paper published in 2021 noted that frequent skin moisturization in early life might promote the development of food allergy, even when skin conditions such as eczema are taken into account.{{cite web |title=Frequent moisturization of infants can lead to food allergies |url=https://www.news-medical.net/news/20210304/Frequent-moisturization-of-infants-can-lead-to-food-allergies.aspx |website=Medical News |access-date=7 August 2022 |date=4 March 2021 |archive-date=19 November 2023 |archive-url=https://web.archive.org/web/20231119150759/https://www.news-medical.net/news/20210304/Frequent-moisturization-of-infants-can-lead-to-food-allergies.aspx |url-status=live }}

Paraffin-based skincare products and contaminated clothing can pose a serious fire hazard. Between 2010 and 2018, paraffin was linked to 50 fire incidents (49 of which were fatal) in the U.K.{{cite web |title=Emollients: new information about risk of severe and fatal burns with paraffin-containing and paraffin-free emollients |url=https://www.gov.uk/drug-safety-update/emollients-new-information-about-risk-of-severe-and-fatal-burns-with-paraffin-containing-and-paraffin-free-emollients |website=GOV.UK |access-date=31 December 2020 |language=en |archive-date=8 November 2020 |archive-url=https://web.archive.org/web/20201108141042/https://www.gov.uk/drug-safety-update/emollients-new-information-about-risk-of-severe-and-fatal-burns-with-paraffin-containing-and-paraffin-free-emollients |url-status=live }} A West Yorkshire Fire and Rescue Service study found that clothing contaminated with cream containing only 21% paraffin, when set alight, was fully engulfed in flame in 3 seconds.{{cite news |title=Fire tests show dangers of paraffin-based skin creams |work=BBC News |url=https://www.bbc.com/news/av/uk-43009261 |access-date=31 December 2020 |archive-date=29 November 2021 |archive-url=https://web.archive.org/web/20211129162633/https://www.bbc.com/news/av/uk-43009261 |url-status=live }} The Medicines and Healthcare products Regulatory Agency (MHRA) released a warning in 2008 about the flammability of paraffin-based products.{{cite web |title=Paraffin-based treatments: risk of fire hazard |url=https://www.gov.uk/drug-safety-update/paraffin-based-treatments-risk-of-fire-hazard |website=GOV.UK |access-date=31 December 2020 |language=en |archive-date=21 February 2022 |archive-url=https://web.archive.org/web/20220221230533/https://www.gov.uk/drug-safety-update/paraffin-based-treatments-risk-of-fire-hazard |url-status=live }} MHRA recommends that regular paraffin users change their sheets regularly, refrain from smoking and/or bringing open flames near paraffin-coated people or objects.{{cite web |title=Paraffin-based skin emollients on dressings or clothing: fire risk |url=https://www.gov.uk/drug-safety-update/paraffin-based-skin-emollients-on-dressings-or-clothing-fire-risk |website=GOV.UK |access-date=31 December 2020 |language=en |archive-date=4 February 2022 |archive-url=https://web.archive.org/web/20220204083840/http://www.gov.uk/drug-safety-update/paraffin-based-skin-emollients-on-dressings-or-clothing-fire-risk |url-status=live }} MHRA also recommends that skin creams containing any paraffin have a flammability warning on the packaging.{{cite web |last1=Goldberg |first1=Adrian |last2=Robinson |first2=Ben |title=Skin creams containing paraffin linked to fire deaths |url=https://www.bbc.com/news/uk-39308748 |website=BBC News |access-date=31 December 2020 |date=19 March 2017 |archive-date=15 December 2020 |archive-url=https://web.archive.org/web/20201215220258/https://www.bbc.com/news/uk-39308748 |url-status=live }}

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