Moisturizer

Moisturizer or emollient[1] is a cosmetic preparation used for protecting, moisturizing, and lubricating the skin. These functions are normally performed by sebum produced by healthy skin.[2] The word "emollient" is derived from the Latin verb mollire, to soften.[3]

White petrolatum

Mechanism of action

In the human body, water constantly evaporates from the deeper layers of the skin through an effect known as transepidermal water loss (TEWL). 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 corneocytes.[4]

Moisturizers modify the rate of water loss, with active ingredients of moisturizers falling into one of two categories: occlusives and humectants[5]

Occlusives form a 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.[5] 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.[4] Oils naturally produced by the human body moisturize through this same mechanism.[2]

Humectants absorb water. They can absorb this water from the air and moisturize the skin when the humidity is greater than 70%, but more commonly they draw water from the dermis into the epidermis, making skin dryer.[6] A study published in Skin Research and Technology in 2001 found no link between humectants and moisturizing effect.[7] When used in practical applications, they are almost always combined with occlusives.[8]

Moisturizers often contain water, which acts as a temporary hydration agent and as a way for the absorption of some components and evaporation of the moisturizer.[9]

Kinds

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.[10][11] Other popular moisturizers are castor oil, cetyl alcohol, cetearyl alcohol, cocoa butter, isopropyl myristate, isopropyl palmitate, lanolin, liquid paraffin, polyethylene glycols, shea butter, silicone oils, stearic acid, and stearyl alcohol.

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

Mineral oils and waxes are insensitive to oxidation or rancidity.[12] 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, with little scientific evidence.

Use

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.[13]

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

Moisturizers are used in disposable napkins to prevent dry skin and napkin dermatitis.

A Cochrane review noted that moisturizers show some beneficial effects in eczema.[14] The same review did not find evidence that one moisturizer is better than another.[14]

Potential health risks

Over-moisturization

Persistent moisturization to the skin from exposure to water may contribute to an allergic reaction or irritant contact dermatitis, and can result in penetration of foreign objects. Changes in the skin's normal ecological environment, in or on the skin, can also support the overgrowth of pathological organisms.[9]

Allergens

Moisturizers containing some aromas or food additives may trigger an immune reaction or even cause users to develop new allergies.[15][16]

There is currently no regulation over use of the term "hypoallergenic", and even pediatric skin products with the label were found to still contain allergens.[17][18] Those with eczema are especially vulnerable to an allergic reaction with lotions and creams, as their compromised skin barrier allows preservatives to bind with and activate immune cells.[19]

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, and an allergic reaction when those foods are later consumed.[15] A paper published in 2020 by researchers at St. George’s, University of London found that "frequent skin moisturization in early life might promote the development of food allergy, most likely through transcutaneous sensitization".[16]

Fire risk

Paraffin based skincare products and contaminated clothing can pose a serious fire hazard.[20] Between 2010 and 2018, paraffin was linked to 50 fire incidents (49 of which fatal) in the U.K.[21] 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.[20] The Medicines and Healthcare products Regulatory Agency (MHRA) released a warning in 2008 about the flammability of paraffin-based products.[22] MHRA recommends that sheets of people using paraffin are changed regularly, and that people refrain from smoking or bringing open flames around patients using paraffin.[23] MHRA also recommends that skin creams containing any paraffin have a flammability warning on the packaging.[24]

Brands of moisturizers

See also

References
  1. Marks, Ronald. Emollients. CRC Press. p. 1. ISBN 978-1-85317-439-1. Retrieved 31 December 2020.
  2. MacDonald, Matthew. Your Body: The Missing Manual. "O'Reilly Media, Inc.". p. 22. ISBN 978-1-4493-9201-7.
  3. Schueller, Randy; Romanowski, Perry. Conditioning Agents for Hair and Skin. CRC Press. p. 111. ISBN 978-1-000-11037-1.
  4. Arza Seidel; et al., eds. (2013), Kirk-Othmer Chemical Technology of Cosmetics
  5. Duffill, Mark; Oakley, Amanda. "Emollients and moisturisers". dermnetnz.org. Retrieved 31 December 2020.
  6. Harwood, Anne; Nassereddin, Ali; Krishnamurthy, Karthik (2020). "Moisturizers". StatPearls. StatPearls Publishing. Retrieved 31 December 2020.
  7. Sagiv, A. E.; Dikstein, S.; Ingber, A. (February 2001). "The efficiency of humectants as skin moisturizers in the presence of oil". Skin research and technology: official journal of International Society for Bioengineering and the Skin (ISBS) [and] International Society for Digital Imaging of Skin (ISDIS) [and] International Society for Skin Imaging (ISSI). pp. 32–35. doi:10.1034/j.1600-0846.2001.007001032.x. Retrieved 31 December 2020.
  8. Publishing, Harvard Health. "Moisturizers: Do they work?". Harvard Health. Retrieved 31 December 2020.
  9. Marino, Christina (2006). "Skin Physiology, Irritants, Dry Skin and Moisturizers" (PDF). Skin Physiology, Irritants, Dry Skin and Moisturizers.
  10. Sethi, Anisha; Kaur, Tejinder; Malhotra, SK; Gambhir, ML (2016). "Moisturizers: The Slippery Road". Indian Journal of Dermatology. 61 (3): 279–287. doi:10.4103/0019-5154.182427. ISSN 0019-5154.
  11. Publishing, Harvard Health. "Choosing a good moisturizer for your skin". Harvard Health. Retrieved 31 December 2020.
  12. Chuberre, B.; Araviiskaia, E.; Bieber, T.; Barbaud, A. (November 2019). "Mineral oils and waxes in cosmetics: an overview mainly based on the current European regulations and the safety profile of these compounds". Journal of the European Academy of Dermatology and Venereology: JEADV. pp. 5–14. doi:10.1111/jdv.15946. Retrieved 31 December 2020.
  13. Tony Burns; et al., eds. (2010), Rook's Textbook of Dermatology (8th ed.)
  14. van Zuuren, Esther J; Fedorowicz, Zbys; Christensen, Robin; Lavrijsen, Adriana PM; Arents, Bernd WM (2017-02-06). "Emollients and moisturisers for eczema". Cochrane Database of Systematic Reviews (Review). 2: CD012119. doi:10.1002/14651858.cd012119.pub2. ISSN 1465-1858. PMC 6464068. PMID 28166390.
  15. Graham, Melissa. "Researchers find link between natural lotions, new food allergies". American Academy of Allergy, Asthma & Immunology. Archived from the original on 2017-11-09. Retrieved 31 December 2015.
  16. "Regular Moisturizer Use on Infant Skin Associated with Food Allergy Onset". ImmunoFrontiers. 30 December 2020. Retrieved 31 December 2020.
  17. Parsons, Julia. "Protect children's skin from unregulated term 'hypoallergenic'". BAYLOR COLLEGE OF MEDICINE NEWS. Retrieved 31 December 2015.
  18. Schlichte, Megan J.; Katta, Rajani (2014). "Methylisothiazolinone: An Emergent Allergen in Common Pediatric Skin Care Products". Dermatology Research and Practice. 2014: 1–4. doi:10.1155/2014/132564. PMC 4197884. PMID 25342949.
  19. Doyle, Kathryn (2013-12-12). "Some skin creams bad news for eczema". Reuters. Retrieved 31 December 2015.
  20. {cite web |title=Fire tests show dangers of paraffin-based skin creams |url=https://www.bbc.com/news/av/uk-43009261 |website=BBC News |access-date=31 December 2020}}
  21. "Emollients: new information about risk of severe and fatal burns with paraffin-containing and paraffin-free emollients". GOV.UK. Retrieved 31 December 2020.
  22. "Paraffin-based treatments: risk of fire hazard". GOV.UK. Retrieved 31 December 2020.
  23. "Paraffin-based skin emollients on dressings or clothing: fire risk". GOV.UK. Retrieved 31 December 2020.
  24. Goldberg, Adrian; Robinson, Ben (19 March 2017). "Skin creams containing paraffin linked to fire deaths". BBC News. Retrieved 31 December 2020.
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