Alpha hydroxy acids (AHA) are becoming a popular alternative to tretinoin in the battle against photo aging because they tend to be less irritating and drying to the skin. They may also be used in conjunction with tretinoin to achieve synergistic benefits.

Often referred to as fruit acids because they are found in plants and foods such as citrus fruits, apples, grapes, sugar cane and sour milk, AHAs have been used to beautify the skin for years. Cleopatra and Marie Antoinette bathed in milk and the upper crust of England softened their skin with red wine.

By breaking down the intracellular bonds of the epidermis AHAs accelerate the sloughing of the superficial dead skin cells and thin the outer layer of the skin. Lactic acid and glycolic acid are two AHAs commonly found in dermatologic preparations.

The concentration of the AHA, the base in which it is transmitted to the skin, and the type of AHA all contribute to how effective a product will be.

In low to medium concentrations (4 to 8%) AHAs are used to improve the appearance of age spots, treat acne and clogged pores, and eliminate warts.

In higher concentrations (8 to 12%) they have been found to reduce fine wrinkles and even out irregular skin coloring. A combination of glycolic acid with bleaching agents such as hydroquinone or kojic acid has proven effective in the treatment of age spots and melasma (the mask of pregnancy).

The vehicle in which AHAs are carried can alter the effectiveness of the concentration. If the base buffers the ARA to control for irritation then a 12% concentration may only be as effective as a 5% unbuffered preparation.

The type of alpha hydroxy acid is also of importance in determin ing how effective the product will be. Glycolic acid consists of smaller molecules and therefore penetrates deeper into the epidermis. In high concentrations it may stimulate realignment of the collagen in the dermis.

Lactic acids have a larger molecular structure so they do not penetrate as deeply However, lactic acids are very effective as chemically enhanced moisturizers. When applied to slightly moist skin products like Lachydrin and Lacticare lotions aid in water retention.

Short of being a biochemist, how do you tell which product is best for you? The first step would be to consult a dermatologist, then it may be a matter of trial and error until you find the product which best suits your skin type.