Hydroxy acids and retinoids in cosmetics
Posted on Tuesday, January 13, 2004
Alpha-hydroxy acids are a special group of nontoxic organic acids found in natural foods and are often commercially referred to as "fruit acids". They are weak organic acids and structurally all of them have one hydroxyl group attached to the alpha position of the acid (first carbon following the acid group). Although they are found in nature in sugarcane (glycolic acid), sour milk (lactic acid), and fruits (malic, citric and tartaric acids), the alpha-hydroxy acids used in dermatological and cosmetic products are usually produced synthetically. Several factors of these acids influence the effects on the skin, such as acid concentration, product pH, amount of free acid present, acid type, vehicle used, duration of exposure, and patient's skin type.

Retinoids include natural and synthetic compounds derived from retinol that show vitamin A activity. The importance of this vitamin became manifest many years ago, when erophtalmia was widely observed in people with a diet poor in this vitamin.  The mechanism of action of retinoids has not been completely elucidated, but these substances have profound effects on the modulation of cellular proliferation and differentiaton. Retinol is used for the treatment of skin aging in a concentration of 0.075%. There are no studies comparing its effectiveness with that of of retinoic acid, although retinol does not appear to be as effective. There are indications that its beneficial effects would be greater at higher concentrations.
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