A group of natural acids found in foods. Alpha hydroxy acids include citric acid (found in citrus fruits), glycolic acid (found in sugar cane), lactic acid (found in sour milk), malic acid (found in apples), tartaric acid (found in grapes), and others.  Various alpha hydroxy acids are applied to the skin (used topically) for moisturizing and removing dead skin cells, for treating acne and improving the appearance of acne scars, for improving the appearance of photo-aged skin, and firming and smoothing skin.