Alpha Hydroxy acids (AHA's) are a class of chemical compounds that occur naturally in fruits, milk, and sugar cane. Although they are called acids they are not to be confused with strong industrial acids such as hydrochloric acid and sulfuric acid.
The AHAs most commonly used in cosmetic products are glycolic acid (which is derived from sugar cane) and lactic acid (the substance that gives you muscle burn when you exercise). Other AHAs used include citric acid (from oranges, lemons, etc.), 2-hydroxyoctanoic acid, and 2-hydroxydecanoic acid. The AHA’s may be obtained from their natural sources or may be made synthetically.
Alpha Hydroxy Acids have been safety used for many years (in fact the use of sour milk baths containing lactic acid goes back to the ancient Egyptians). In response to concerns raised by FDA, the cosmetic industry asked the Cosmetic Ingredient Review (CIR) to conduct an independent assessment of the safety of AHAs.
To support this assessment, the cosmetic industry conducted studies to measure whether or not AHAs might increase the sensitivity of the skin to UV light from sun exposure. When these studies were completed, all of the available information, including additional studies conducted by FDA, were carefully reviewed by the CIR Expert Panel.
The CIR Expert Panel noted that the data showed that there was a small, but statistically significant, increase in the sensitivity of the test subjects to UV radiation. The Expert Panel commented that the increase in UVR damage associated with AHA pretreatment was so slight that, in most cases, the ordinary components of a product would be sufficient to eliminate the effect. For example, inclusion of a sunscreen with an SPF of 2 would eliminate the effect. Likewise, addition of color additives or vehicles that produce even a small increase in the ability to reflect UV radiation would eliminate the effect.
The CIR Expert Panel concluded that, even though the effect is small, some steps should be taken to minimize the potential that use of AHA ingredients would result in increased sun sensitivity. They recommended that cosmetics containing AHA ingredients be formulated so as to avoid increasing sun sensitivity or to provide directions for use that include the daily use of sun protection (a SPF product).
The Expert Panel expanded on the meaning of daily use of sun protection to include the American Academy of Dermatology (AAD) recommendations. The AAD recommends avoiding the sun between the peak hours of 10:00 am and 4:00 pm, using a sunscreen with an SPF of 15 or greater and wearing protective clothing and hats.
In March 2000, the FDA reported that studies sponsored by its Office of Women’s Health had found that increased sensitivity to UVR results from applying a cream containing glycolic acid, which the FDA has said it believes has effects similar to other AHAs. Study participants’ sensitivity to skin reddening produced by UVR increased by 18% and their sensitivity to UVR-induced cellular damage doubled on average, with considerable variations among individuals.
The FDA-sponsored studies also indicated, however, that the increased sensitivity quickly reverses after a person stops using the product. One week after the application of the cream to the participants’ skin was stopped; the researchers found that treated skin areas were not significantly more sensitive to UVR than untreated skin areas.
In June 2000, the cosmetic industry submitted a Citizens Petition to the Food and Drug Administration asking them to establish a regulation requiring AHA products, formulated to function as exfoliants, to be labeled with a sun alert statement instructing consumers to “have adequate sunscreen protection while using this product and for a week after you discontinue use.”
After considering this request, FDA published formal guidance in July 2005, that encourages manufacturers to label their products with the following statement: "Sunburn Alert: The product contains an alpha hydroxy acid (AHA) that may increase your skin's sensitivity to the sun and particularly the possibility of sunburn. Use a sunscreen, wear protective clothing, and limit sun exposure while using this product and for a week afterwards.”
Read the FDA Guidance on AHAs
The CIR Expert Panel concluded that AHA ingredients are safe for products formulated for home use when used at lower concentrations and controlled pH of the formula and for professional use at higher concentrations at slightly lower pH. The panel further required that home use products be formulated to avoid increased sun sensitivity or that the use of daily sun protection be advised. For professional products the panel recommended that they be applied by a trained professional for brief and discontinuous use followed by directions for the daily use of sun protection.
It should be noted that, in a study that was completed after the CIR review was issued, a clinical test with 12 healthy subjects using commercial skin creams containing 4 and 8% (low levels) Glycolic Acid and sunscreens (SPF 4), both at pH 3.8, reported that there was no measurable damage to the skin, supporting the conclusion that AHAs can be formulated to avoid increasing sun sensitivity. The sample size on this study was quite small and may not be meaningful to readers with experience in this area.
Why are sunscreens added to Alpha Hydroxy Acids?
As discussed above, sometimes small amounts of a sunscreen ingredient may be included in an AHA product to protect against any increased sensitivity to sunlight that might occur during use.
Does the use of Alpha Hydroxy Acids increase the incidence of skin cancer?
Studies have not found that AHA-containing products contribute to an increase in the incidence of skin cancer.
The National Toxicology Program (NTP) conducted a study to determine if simulated sunlight increased cancer in mice whose skin was treated with Glycolic Acid. No increase in tumors over those mice exposed to simulated sunlight alone was observed.
Read the NTP Report on AHAs.