Alpha Hydroxy Acids: Miracle Workers or Skin Wreckers?
Alpha-Hydroxy Acids: Good for the Skin?
Alpha-hydroxy acids (AHAs) are lauded by the cosmetic industry and even dermatologists for their alleged anti-ageing properties. AHAs are a group of acids derived from a variety of sources, including fruit and milk sugars. There are a range of AHAs used in cosmetic products, including: glycolic acid, lactic acid, malic acid, tartaric acid, citric acid, ammonium glycolate, ammonium alpha-hydroxyethanoate and alpha-hydroxyethanoic acid. They are used in cosmetic products as exfoliants to remove the outer layer of skin, supposedly revealing fresher, younger, smoother looking skin underneath, and as moisturisers and emollients. Dermatologists and cosmetic surgeons use AHAs in much higher concentrations than cosmetic products (between 20 and 70 per cent), to reduce the signs of aging and treat chemical disorders, in the form of chemical or facial peels.
The AHAs used in cosmetics are synthetic. Since 1989 the U.S. FDA has received over 100 reports of adverse reactions in individuals using AHA, including bleeding, blistering, rashes, skin discolouration and stinging. The FDA believes that reactions are probably much more common, suggesting that for every report of an adverse reaction received by the agency, between 50 and 100 are received by the manufacturer. John Bailey, Ph.D., former director of the FDA’s Office of Cosmetics and Colours stated in 1998 that, “This would translate into approximately 10,000 adverse reactions being received for AHA-containing products.” 1
It has been suggested that AHAs may cause the skin to age more rapidly and elevate the risk of skin cancer, due to their ability to remove the outer layer of skin which can elevate sensitivity to sunlight, thereby increasing photo-ageing. In one study the AHA glycolic acid elevated the sensitivity of human skin to sunburn by as much as 50 per cent in some individuals. 2
Research carried out on guinea pigs found that the AHA glycolic acid caused skin damage, with higher doses altering the structure of the skin and destroying some parts of the epidermal layer, as well as increasing UVB-induced skin damage, to a far greater degree than either glycolic acid or UVB in isolation. 3
Alpha hydroxy acids are water soluble, Beta hydroxy acids (BHAs) are lipid (oil soluble.) Beta hydroxy acids are believed to cause less irritation than AHAs and they are allegedly able to reduce fine lines and wrinkles. According to the U.S. FDA BHAs may be listed as salicylic acid (or related substances – salicylate, sodium salicylate, and willow extract) – although from a chemist’s point of view this substance is not a genuine BHA but it is referred to as one by cosmetic companies – beta hydroxybutanoic acid, tropic acid and trethocanic acid. 4
Salicylic acid (a metabolite of aspirin) can penetrate the skin and approximately 10 per cent of applied salicylates can remain in the skin. It is irritating to the skin, mucous membranes and epithlial cells. 5 In animal studies parental exposures to salicylic acid caused reproductive and developmental toxicity. Salicylic acid also strips away the horny outer layer of the skin, prompting concerns that repeated use could enhance the risk of damage from UV radiation. 6 Those who have allergic skin reactions to aspirin may also react to topically applied salicylic acid.
In the U.S., following concerns raised by the FDA about AHAs increasing sensitivity to sunlight, the Cosmetic Ingredient Review (CIR) carried out an independent safety assessment of AHAs and found a small increase in sun sensitivity amongst study participants exposed to UV radiation, after being pretreated with AHAs. Therefore the CIR Expert Panel recommended that concentrations of AHA’s used in cosmetic products be restricted to 10 per cent or less in the final formulation with a pH of 3.5 or below and that products containing AHAs should be formulated to avoid elevating sensitivity to sunlight or directions for daily sun protection use should be highlighted on the label. The concentration limit is higher (up to 30 per cent) for professional products.
1) Kurtzweil, P., ‘Alpha Hydroxy Acids for Skin Care: Smooth Sailing or Rough Seas,’ U.S. Department of Health and Human Services, U.S. Food and Drug Administration, Centre for Food Safety and Applied Nutrition (CFSAN), Office of Cosmetics and Colours, FDA Consumer, College Park, MD, March – April, 1998; Revised May, 1999; online at: www.cfsan.fda.gov.
2) ‘NICNAS: Priority Existing Chemical Assessment Report,’ Australian Government, Department of Health and Aging, National Industrial Chemicals Notification and Assessment Scheme (NICNAS), Marrickville, NSW, 2000 (12): 128; online at: www.nicnas.gov.au.
3) Park, K.S. et al, Effect of Glycolic Acid on UVB-Induced Skin Damage and Inflammation in Guinea Pigs, Skin Pharmacology and Applied Skin Physiology, July-August, 2002: 15 (4): 236-245.
4) ‘Beta Hydroxy Acids in Cosmetics,’ U.S. Department of Health and Human Services, U.S. Food and Drug Administration, Centre for Food Safety and Applied Nutrition, Office of Cosmetics and Colours, College Park, MD, March 7, 2000; online at: www.cfsan.fda.gov.
5) Gilman, A.G., Rall, T.W., Nies, A.S., Taylor, P. (Eds), Goodman and Gilman’s The Pharmacological Basis of Therapeutics, 8th Edition, Pergamon Press, 1990, p 649.
6) Safety Assessment of Salicylic Acid, Butyloctyl Salicylate, Calcium Salicylate, C12-15 Alkyl Salicylate, Capryloyl Salicylic Acid, Hexyldodecyl Salicylate, Isocetyl Salicylate, Isodecyl Salicylate, Magnesium Salicylate, MEA-Salicylate, Ethylhexyl Salicylate, Potassium Salicylate, Methyl Salicylate, Myristyl Salicylate, Sodium Salicylate, TEA-Salicylate, and Tridecyl Salicylate, International Journal of Toxicology, 2003: 22 (3): 1-108.
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