Spotlight On: Alpha Hydroxy Acids

Ingredients, Skin Care

Alpha hydroxy acid products are the jeans of the skincare world: they have been used for years, but they’re not going anywhere anytime soon. And for good reason: According to Dr. David E. Bank, author of Beautiful Skin, alpha hydroxy acids cause increase exfoliation of the outer layer of skin, unplog pores, and function as a humectant to hydrate the skin. Bank also mentions that AHAs have further been shown to stimulate collagen and elastin production in the dermis. Dr. Leslie Baumann, author of Cosmetic Dermatology, further adds that AHAs have been reported in improving mottled pigmentation, fine lines, surface roughness, freckles, lentingines, and to treat actinic and seborrehic keratosis. AHAs seem to be an excellent addition to one’s skincare regime, if not already present.

What exactly is an alpha hydroxy acid?

Alpha hydroxy acid” is a name for a group of naturally occurring compounds that feature the hydroxy (-OH) group in the α position (that is, attached to the carbon that is adjacent to the -COOH carbon). Alpha hydroxy acids commonly found in skincare treatments include glycolic acids and lactic acid.

What does glycolic acid do?

Glycolic acid is the most common of all the alpha hydroxy acids. Glycolic acid peels advance desquamation and thinning of the stratum corneum (the uppermost layer of the skin). By exfoliating the top layer of the skin, glycolic acid peels smooth the skin, quicken the rate of cell turnover (which is reduced by up to 7% every ten years), decrease small wrinkles and increase the fibroblast proliferation of collagen.

What glycolic acid treatments are available? Are they all effective?

A glycolic acid peel, known as “the lunchtime peel” because it can be completed over a patient’s lunch hour, and often inconspicuously, is available from the dermatologist in concentrations ranging from 20 percent to 70 percent (pH as low as 3.0). Most dermatologists recommend that the patient undergo a series of six weekly treatments at a cost of $150-$200 per peel, and gradually building up the concentration and contact time with each peel. Baumann notes that it usually takes at least four peels for noticeable improvement of photodamage, solar lentigos, and melasma to occur. However, both treatment and results may vary based upon the patient.

Glycolic acid is also available in at-home treatments in 8 to 15 percent concentrations (pH about 3.5 or higher); it is typically diluted with anti-irritating ingredients in a mild formula. At these low concentrations, Baumann notes that the patient should not expect reversal of moderate to severe wrinkling or scarring. In fact, according to a randomized, placebo-controlled double-blind study, it was found that 0.05% all-trans-retinoic acid was more effective than 2% lipoic acid or 10% glycolic acid (a concentration found in at-home treatments) in treating signs of aging. The user should also be cautious of irritation with at-home treatments. Baumann cites a study by Yu et. al which found that certain other ingredients in formulations containing AHAs cause irritation, rather than the AHAs themselves. The buyer is thereby advised to be extremely cautious in selecting proper at-home glycolic acid treatments. Dr. Bank recommends NeoStrata Skin Smoothing Cream with 8 percent glycolic acid, and Aqua Glycolic Face Cream ($17.49,

What is lactic acid? How do its effects differ from glycolic acid?

Lactic acid, extracted from milk but usually found in synthetic form in most cosmetics, is another popular AHA, but unlike glycolic acid, it is primarily used in out-of-office treatments. One source of lactic acid is in LacHydrin, a prescription drug FDA approved to treat (surprise!) dry skin, not signs of aging, although the latter is also assisted with LacHydrin use. The fact that LacHydrin does both makes it an excellent recommendation for post-menopausal women, who often experience dry skin and signs of aging. For anti-aging treatments, glycolic acid is usually preferred to lactic acid because it has a smaller molecular structure, which allows it to easily and efficiently penetrate the skin, and also because glycolic acid increases the thickness and firmness of the skin, but lactic acid does not.

Don’t lactic acid and glycolic acid cause skin dryness?

Despite popular belief, it seems that lactic acid and glycolic acid do not cause skin dryness or irritation; rather, it is often the formulation (i.e., the other ingredients) of the AHA treatment that is the source of discomfort, as found in a previously mentioned study by Yu et. al. A second Baumann-cited study found that transepidermal water loss (TEWL) is not altered by application of AHAs. In fact, AHAs are humectants that increase the ability of the skin to hold onto water, as evidenced by the fact that lactic acid is the main ingredient in LacHydrin, an FDA-approved drug for the treatment of dry skin. One probable reason AHAs are commonly blamed for dry skin and irritation is because stronger peels, such as the deep phenol or medium depth trichloracetic acid (TCA) peels, often cause skin sensitivity and irritation. However, typical strength glycolic and lactic acid peels are actually considered “superficial,” usually without many of the side effects of medium-and-deep strength or laser treatments.

Do AHAs make skin more photosensitive or thin the skin?

AHAs have been found to thin the epidermis, and make skin more photosensitive. A Baumann-cited study conducted by Tsai et. al found that pre-treatment with 10% glycolic acid caused an increase in UVB sensitivity in white and Asian subjects, and an increase in UVA sensitivity in Asian subjects. This is a clear indication that AHAs must be used with regular sun protection.

The epidermis is thinned after use of AHAs. However, interestingly, the overall thickness of the skin is increased after use of glycolic acid, as treatment has been shown to increase expression of Type 1 Collagen mRNA and hyaluronic acid content in the dermis of the skin. However, after lactic acid treatment, a 1996 study by Smith et. al found no change in dermal thickness or firmness.


When administered by a licensed dermatologist, AHA treatments have been proven effective in fighting fine lines, dryness, and other signs of photoaging. AHAs also stimulate collagen levels and smooth the skin, giving it a luminous appearance. However, many at-home treatments (usually of about 10% glycolic acid) have been associated with formulation-derived irritation and less efficacy when compared to other options, like 0.05% all-trans-retinoic acid (tretinoin, a retinoid). Overall, it seems that AHA treatments are highly effective and relatively gentle anti-aging treatments, but when administered by a dermatologist rather than via at-home treatments.

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