Both alpha and beta hydroxy acids are used in skin care treatments to exfoliate or peel. Alpha hydroxy acids (AHAs) are also known as fruit acids, as they are found in citrus fruits, apples and grapes. They are also found in corn, sugar cane and milk. They share a common chemical structure consisting of a hydroxyl group on the alpha carbon position. Examples include malic acid, lactic acid, citric acid and glycolic acid.
Beta hydroxy acids (BHAs) have a slightly different chemical structure and are less commonly used. In skin care, salicylic acid is the main beta hydroxy acid, but also look on the label for beta hydroxybutanoic acid, tropic acid or trethocanic acid. A significant difference between the two is that alpha hydroxy acids are water soluble, while beta hydroxy acids are oil soluble.
Both alpha and beta hydroxy acids are becoming increasingly popular in skin care products such as toners, moisturizers, sunscreen and cleansers.
Advertising campaigns claim their effects include improved acne, a decrease in the appearance of wrinkles, diminished excess pigmentation spots, moisturizing and tightening the skin, removing sun damage, and improving underlying collagen and elastic tissues in the skin.
There is little if any scientific data to back up these claims, however.
Alpha hydroxy acids are able to decrease the strength of cell-to-cell bonding so the outer layer of dead skin, the stratum corneum, peels off in sheets. This results in increased moisturization of the upper layer of skin. Wrinkles are smoothed out as a result. AHAs are used for refreshing damaged skin.
Beta hydroxy acid is also used for exfoliation and improved skin tone. Since BHAs are more oil soluble, they may be better for oily skin types and better at treating acne. These also tend to cause less irritation than AHAs.
Safety of AHAs
By removing the upper protective stratum corneum layer of the skin, AHAs make the skin more sensitive to sunburn. Reported side effects include photosensitivity, dryness, scaling and burning. Some users are more sensitive to the side effects of AHAs than others and are more prone to the side effects.
The Cosmetic Ingredient Review (CIR) expert panel of the CTFA (now the Personal Care Products Council) reviewed consumer-reported side effects and human clinical studies in 1998 to come up with reasonable safety suggestions.
It was determined that AHAs such as glycolic acid and lactic acid are safe in cosmetic products at concentrations of less than 10 percent, and a final formulation pH of greater than 3.5, AHAs are safe for use in salons in the hands of trained aestheticians at concentrations of 20 percent to 30 percent and a final pH of greater than 3.
At this concentration, AHAs are used as a light epidermal peel and only for brief and discontinuous use when rinsed off the skin. Above this concentration, the CIR recommends that these only be used by dermatologists as a chemical peel.
As concentrations increase, the risk of skin irritation also increases. Side effects include burning sensations, dermatitis or rash, swelling, pigment changes, blisters or welts, skin peeling, itching, irritation or tenderness, chemical burns and increased risk of sunburn.
Safety of BHAs
The CIR expert panel evaluated the safety of salicylic acid, the main ingredient of BHAs, as a cosmetic ingredient in 2000, but has not reviewed it since. It determined that salicylic acid is safe when used properly and formulated to avoid irritation and sun sensitivity. Long-term safety, however, has not been established for either BHAs or AHAs.
Consumers should carefully read cosmetic labels. Any product containing either an AHA or BHA should be tested first on a small area of skin before widespread use on the body. These products should not be used on infants or children. Sunscreen should be used if using an AHA or BHA product, as the skin's sensitivity to sun may increase with use.