Volume 32, Issue 6, Page 29 (June 2001)

The use of hydroxy acids in skin care products dates back to Cleopatra, who is said to have applied sour milk to her face to enhance its youthfulness.

Authors have reported success using alpha-hydroxy acid (AHA) products in the treatment of photoaging by improving mottled pigmentation, fine lines, surface roughness, freckles, and lentigines. AHAs have also been used with success to treat actinic and seborrheic keratosis (J. Dermatol. Surg. Oncol. 18[6]:495-98, 1992).

AHAs are a family of naturally occurring organic acids. Glycolic acid, derived from sugarcane, is most commonly used for in-office superficial peels and for at-home preparations. Other AHAs include lactic acid, derived from sour milk; malic acid from apples; citric acid from citrus fruits; tartaric acid from grapes; and phytic acid from rice.

The structure common to all AHAs is a terminal carboxyl group with one or two hydroxyl groups on the second, or alpha, carbon, and a variable-length carbon chain. This structure gives AHAs their water solubility and hydrophilic properties. Although these AHAs are derived from organic ingredients, the majority of those used in cosmeceuticals are chemically produced.

AHAs walk the line between being a cosmetic and being a drug. They have come under scrutiny by the Food and Drug Administration following reports that apoptotic "sunburn cells" have been seen in patients treated with AHA products.

A more recent unpublished study, presented by Dr. E. Schachler at the International Symposium on Cosmetic Efficacy, held in New York in 1999, demonstrated that AHAs indeed have a biologic activity and could technically be considered drugs.

In this study, Dr. Schachler showed that cytokine production was recorded when AHA was applied to cultured keratinocytes. The types of cytokines produced by these cells were altered when AHA was placed in these cell cultures.

AHAs have been shown to be effective in reversing the signs of dermal and epidermal aging. They reduce intercorneocyte cohesion directly above the granular layer, advancing desquamation and leading to even thinning of the stratum corneum.

This improves skin surface flexibility because a thin stratum corneum bends more easily without fissuring or cracking.

These exfoliant properties make them desirable as smoothing and "antiaging" products, because the exfoliation process becomes less efficient with age.

In the mid-1990s, Dr. Cherie Ditre and her associates observed a significant increase in epidermal thickness, reversal of basal cell atypia, and dispersal of melanin pigmentation due to the application of AHAs.

The investigators also noted increased glycosaminoglycans and collagen synthesis, enhanced quality of elastic fibers, and elevated fibroblast proliferation (J. Am. Acad. Dermatol. 34[2, pt. 1]:187-95, 1996).

Studies on glycolic acid used in vivo and in vitro have also shown the ingredient to increase collagen production and fibroblast proliferation (Dermatol. Surg. 24[10]:1054-58, 1998; Dermatol. Surg. 22[5]:439-41, 1996).

Moisturizers containing AHAs range in concentration from 2% to 20%, with glycolic acid being the most commonly used AHA.

When formulated properly, AHAs are excellent ingredients for the treatment of photoaging and dry skin. It is important to remind patients that AHA products can be irritating to patients with sensitive skin and rosacea. The irritation induced by some AHA products has been shown to be related to the formulation of the product rather than the AHA itself (Cosmet. Dermatol. 9[5]:40-44, 1996).

In fact, AHAs have actually been shown to decrease skin irritation. One randomized, double-blind, vehicle-control study found that AHAs—specifically glycolic acid, lactic acid, tartaric acid, and gluconolactone—protected the skin from irritation caused by a 5% sodium lauryl sulfate challenge patch test, as measured by resulting erythema and changes in transepidermal water loss (TEWL).

The researchers found that TEWL is not adversely altered by application of AHAs. In fact, it has been suggested that lactic acid may help improve the skin barrier by increasing levels of ceramide linoleate, thereby decreasing TEWL (Acta Derm. Venereol. 78[1]:27-30, 1998).

Lactic acid is also available in a prescription form (Lac-Hydrin 12% cream). Several studies on the activity of this product have documented its moisturizing ability. Many think lactic acid may be a part of the skin's natural moisturizing system, which may give it superior moisturizing effects, compared with other AHAs (Cosmet. Toiletries 93:85-86,1978).

Lactic acid also has been shown to have antiaging benefits and effects on desquamation similar to those seen with glycolic acid. It is generally not used as an in-office peel.

Although AHAs are very popular in daily cleansers and moisturizers, some experts have suggested that continued AHA use may result in a decrease in efficacy due to accommodation by the skin. It is believed that continued exposure to AHA enhances the skin's ability as an acid buffer, allowing it to more efficiently neutralize the effects of the acids (J. Am. Acad. Dermatol. 35[3, pt. 1]:388-91, 1996).

Although there is currently no published evidence to support this claim, it must be kept in mind.

It may be beneficial to have patients stop the use of AHA preparations periodically to enhance the long-term efficacy of these products.

AHAs may increase photosensitivity; therefore, patients using these products should be advised to apply sunscreens.
DR. LESLIE BAUMANN is director of cosmetic dermatology at the University of Miami. Melissa Lazarus, a research fellow at the university, contributed to the column. To respond to this column, write to Dr. Baumann at our editorial offices.

© 2001 International Medical News Group. Published by Elsevier Inc. All rights reserved.