Alpha hydroxy acids, or AHAs, (A-H-As) are a group of chemicals that are used to encourage the turnover of skin cells. This thinning of the outer layer of skin often improves the appearance of fine lines, age spots, dryness, and acne blemishes. Two common alpha hydroxy acids are glycolic (gly-CALL-ic) acid, made from sugar cane, and lactic (LAK-tic) acid, produced from milk. These acids are found in many creams, cleansers, and other cosmetic products, typically in strengths of 10 percent or less. In higher concentrations up to 70 percent, AHAs are used by dermatologists to perform light skin peels. The acid preparation is applied to the skin for several minutes. During this time, you may feel tingling, warmth, or even a mild burning. The acid is then neutralized and rinsed off. While AHAs can help your skin look better, they may also make you more vulnerable to sunburn and sun damage. The daily use of sun block is therefore advised for anyone receiving peels or using AHA products. Some people report adverse reactions to these acids, including severe redness, burning, itching, swelling, and discoloration. If you experience problems, stop using the product and see a doctor right away. Because AHAs are relatively new, their long-term effects on the skin are unknown.