AHAs are derived from various plant sources or from milk. However, 99% of the AHAs included in cosmetics are synthetic. In low concentrations (less than 3%) AHAs work as water-binding agents. At concentrations over 4% and in a base with an acid pH of 3 to 4, these can exfoliate skin cells by breaking down the substance in skin that holds skin cells together. The most effective and well-researched AHAs are glycolic acid and lactic acid. Malic acid, citric acid, and tartaric acid may also be effective, but are less stable and less skin-friendly; there is little research showing that they have any benefit for skin.

AHAs may irritate mucous membranes and cause irritation. However, AHAs are widely used for therapy of photodamaged skin, and also have been reported to normalize hyperkeratinization (over-thickened skin) and to increase viable epidermal thickness and dermal glycosaminoglycans content. A vast amount of research has substantially described how the aging process affects the skin and has demonstrated that many of the unwanted changes can be improved by topical application of AHAs, including glycolic and lactic acid.

To find out if a cosmetic contains an AHA, look on the list of ingredients all cosmetics must, by law, have on their outer packaging. AHA ingredients may be listed as:
1. Glycolic acid
2. Lactic acid
3. Malic acid
4. Citric acid
5. Glycolic acid + ammonium glycolate alpha-hydroxyethanoic acid
6. Ammonium alpha-hydroxyethanoate
7. Alpha-hydroxyoctanoic acid
8. Alpha-hydroxycaprylic acid
9. Hydroxycapry lie acid
10. Mixed fruit acid
11. Tri-alpha hydroxy fruit acids
12. Triple fruit acid
13. Sugar cane extract
14. Alpha hydroxy and botanical complex L-alpha hydroxy acid
15. Glycomer in crosslinked fatty acids alpha nutrium (three AHAs)

AHAs are generally safe when used on the skin as a cosmetic agent using the recommended dosage. The most common side-effects are mild skin irritations, redness and flaking. The severity usually depends on the pH and the concentration of the acid used. Chemical peels tend to have more severe side-effects including blistering, burning and skin discoloration, although they are usually mild and go away a day or two after treatment.

The FDA has warned consumers that care should be taken when using AHAs after an industry-sponsored study found that they can increase photosensitivity to the sun. This is because AHAs exfoliate sun-damaged skin from the surface of the skin, and because this layer imparts some (albeit minimal) sun protection for skin. Wearing a sunscreen can eliminate this risk. Or better yet, use products with AHA at night.

An example of a product with AHA is Estee Lauder’s Frution Extra Multi-Action Complex.

Source: Wikipedia, Y2K Health and Detox Center, Don’t Go To The Cosmetics Counter Without Me by Paula Begoun