Alpha Hydroxy Acids

The following information is intended to answer questions about alpha hydroxy acids, also known as AHAs, which are often used as ingredients in cosmetic and drug products applied to the skin.

How do AHAs work? 

AHA-containing products cause exfoliation, or shedding of the surface skin. The extent of exfoliation depends on the type and concentration of the AHA, its pH, and other ingredients in the product.

What about products that contain AHAs and are marketed with therapeutic claims? 

Some products containing AHAs have been marketed for uses such as treating acne, removing scars, and lightening discolorations. Among these are some products marketed as “skin peelers,” which may contain relatively high concentrations of AHAs or other acids and are designed to remove the outer layer of the skin. Products that are intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease, or to affect the structure or any function of the body are drugs under the law (Federal Food, Drug, and Cosmetic Act, Sec. 201(g)). For example, products intended for use as acne treatments or skin lighteners are considered drugs. 

Has the FDA received reports of adverse events related to AHAs? 

FDA received a total of 114 adverse dermatologic experience reports for AHA-containing skin care products between 1992 and February 2004, with the maximum number in 1994. The reported adverse experiences included burning (45), dermatitis or rash (35), swelling (29), pigmentary changes (15), blisters or welts (14), skin peeling (13), itching (12), irritation or tenderness (8), chemical burns (6), and increased sunburn (3). The frequency of such reports for skin exfoliating products that contain AHAs has been considerably lower in subsequent years. The more serious adverse reactions appear to occur most often with products that cause the greatest degree of exfoliation, such as “skin peelers.”

Has the FDA conducted research on the safety of AHAs? 

Yes. These studies (1) compared the effect of AHAs, topically applied in a cream, on the sensitivity of human skin to ultraviolet (UV) radiation with the effect of the same cream containing no AHAs, (2) measured how fast the skin returns to normal after use of the AHA-containing cream is discontinued, and (3) investigated whether AHAs enhance UV-induced damage to DNA in the skin (Kays Kaidbey, Betsy Sutherland, Paula Bennett, Wayne G. Wamer, Curtis Barton, Donna Dennis, and Andrija Kornhauser, Topical glycolic acid enhances photodamage by ultraviolet light, Photodermatology, Photoimmunology and Photomedicine, vol. 19 (2003), issue 1, pages 21-27).

These studies confirmed previous industry studies indicating that applying AHAs to the skin results in increased UV sensitivity. After four weeks of AHA application, volunteers’ sensitivity to skin reddening produced by UV increased by 18 percent. Similarly, the volunteers’ sensitivity to UV-induced cellular damage doubled, on average, with considerable differences among individuals.

However, the studies also indicated that this increase in sensitivity is reversible and does not last long after discontinuing use of the AHA cream. One week after the treatments were halted, researchers found no significant differences in UV sensitivity among the various skin sites.

The studies did not identify exactly how AHAs bring about the increased UV sensitivity, although the effects did not appear to involve dramatic increases in UV-induced damage to DNA in the skin.

Previous FDA studies have indicated that a cosmetic-type cream base caused an AHA to penetrate more deeply into the skin when compared to an AHA solution without the usual cosmetic ingredients. However, further studies will be needed to learn how much, if at all, those cosmetic-type ingredients influence the AHA-related effects on UV sensitivity.

FDA also has collaborated with the National Toxicology Program (NTP) to assess the safety of the long-term use of AHAs. This study determined that glycolic acid did not affect photocarcinogenesis (the development of cancer cells associated with exposure to light) in mice, and that salicylic acid had a photoprotective effect (protected against the effects of light) in mice. The complete results of this study are available in the NTP Technical Report on the Photocarcinogenesis Study of Glycolic Acid and Salicylic Acid (CAS Nos. 79-14-1 and 69-72-7) in SKH-1 Mice (Available in PDF (1.9MB)).

How can AHAs be used safely? 

It is important to follow directions carefully and heed any warning statements on the label when using any cosmetic product. If you are using AHAs, it is advisable to use sun protection.

The purpose is to educate consumers about the potential for increased skin sensitivity to the sun from the topical use of cosmetics containing AHAs and to educate manufacturers to help ensure that their labeling for these products is not false or misleading.

FDA recommends that the labeling of a cosmetic product that contains an AHA as an ingredient and that is topically applied to the skin or mucous membrane, such as the lips, bear a statement that conveys the following information:

Sunburn Alert: ,,This product contains an alpha hydroxy acid (AHA) that may increase your skin’s sensitivity to the sun and particularly the possibility of sunburn. Use sunscreen, wear protective clothing, and limit sun exposure while using this product and for a week afterwards.’’

Based on industry-sponsored studies, the Cosmetic Ingredient Review Expert Panel — the industry’s self-regulatory body for reviewing the safety of cosmetic ingredients — concluded that products containing the AHAs glycolic and lactic acid are safe for use by consumers if:

• The AHA concentration is 10 percent or less.
• The final product has a pH of 3.5 or greater.
• The final product is formulated in such a way that it protects the skin from increased sun sensitivity or its package directions tell consumers to use daily protection from the sun.

The most common AHAs in cosmetic products are glycolic acid and lactic acid. Among others are citric acid, hydroxy caprylic acid, and hydroxy capric acid.

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