Alpha-hydroxy acids are commonly found and isolated from fruits of all sorts. That is why they are referred to as fruit acids. For example, malic acid is found in apples, citric acid can be isolated from most citrus fruits and glycolic acid is commonly found in honey and sugar cane. Lactic acid is found in milk that has soured and Tartaric acid can be isolated from fermented grapes (wine). . Glycolic acid works as an exfoliating agent because of its high acidity but easy solubility. When placed on the skin as part of an exfoliating cream or gel, glycolic acid goes under the damaged upper layers of skin and destroys the 'glue', which holds dead skin to the surface. As this dead skin is chemically burned off, the other ingredients carry the individual flakes away and a water rinse neutralizes the remaining acid. The result is a much-smoother skin surface and a more youthful appearance. A secondary benefit is glycolic acid's ability to draw moisturizers into the newly exfoliated skin surface. One study showed that topical treatment twice a day for 3 months with 5% glycolic acid cream at pH 2.8 affected surface and epidermal changes, while the same treatment, but with a 12% cream reached deeper and influenced both the epidermis and the deeper dermis layer, and resulted in increased epidermal and dermal firmness and thickness. Both showed clinical improvement in skin smoothness and in the appearance of lines and wrinkles. Another study showed that AHAs might thin the outer stratum corneum, but actually end up increasing the overall thickness of the epidermis. This thickening is accompanied by increased synthesis of collagen. It is apparent that alpha-hydroxy acids may do more than just increase exfoliation and skin cell turnover.