Sustained by the quest for a youthful appearance, the use of alpha-hydroxy acids (AHAs) in skin
care products has grown dramatically throughout the last decade. Advertising and labeling for
these products claim, among other things, that they reduce wrinkles, spots, and other signs of
aging. Despite these claims that AHAs bring about substantial changes in the skin, there is little
information about their long-term safety.
Recent studies sponsored by FDA's Office of Women's Health have confirmed that applying an
AHA to the skin can make people more susceptible to the damaging effects of the sun, including
sunburn. However, these studies also indicate that - at least in the case of glycolic acid, the AHA
most commonly used in cosmetics - this change tends to be quickly reversible after a person
stops using the product.
An analysis of the results will be published in scientific journals. The full text of the study
reports will be made available in the near future.
The cosmetic industry has previously sponsored several clinical studies on this subject. These
studies have shown that topical application of glycolic acid causes an increase in sensitivity to ultraviolet (UV) radiation. In other words, when exposed to the sun, people tend to burn more easily when they are using AHAs on their skin.
During FDA's independent review of the available data on AHA-induced sensitivity to UV, the agency found several questions unanswered. Among these were -
- How long does the increased UV sensitivity last after a consumer stops using the product?
- Do other ingredients - those that make up the cream or lotion base of the product - influence the way AHAs affect UV sensitivity?
- How do AHAs bring about this increase in UV sensitivity? For instance, do AHAs affect the sensitivity of the DNA in skin to damage by sunlight?
How FDA's Studies Were Conducted
The FDA-sponsored studies involved Caucasian volunteers with varying degrees of susceptibility to sunburn. Each volunteer underwent exposure of small patches of skin to UV light. In one study, researchers compared the effects of UV light on -
- patches of skin that received applications of glycolic acid in a cream base,
- patches of skin that received applications of the same cream, but without glycolic acid, and
- patches of skin that received neither the glycolic acid cream nor the plain cream.
The cream base used in the studies was similar to that contained in a number of cosmetic products.
What the Studies Showed
These studies confirmed the previous findings 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%. 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.
Advice to consumers
Based on the 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 under the following conditions:
- 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.
FDA's own studies suggest that if you are using AHAs, it is advisable to use sun protection. It also is important to follow directions carefully and heed any warning statements on the label.