What are Alpha Hydroxy Acids?

Alpha hydroxy acids are a group of organic carboxylic compounds that are produced both naturally and industrially. Some of the natural types of alpha hydroxy acids include:

• Citric Acid: Found in citrus fruits

• Lactic Acid: Found in milk and pickled products

• Glycolic Acid: Derived from sugarcane

• Malic Acid: Found in apples

• Tartaric Acid: Found in grapes

Note: Among the different types of AHA, lactic, citric, and glycolic acids are used in cosmetic products for skin health.

Structure and Physical Properties of Alpha Hydroxy Acids

There are several types of acids in the alpha hydroxy acids group. In these molecules, one or more hydroxyl functional groups are attached to the alpha carbon (the first carbon next to the acid group). Tartaric acid is a dicarboxylic acid with two hydroxyl groups located at the alpha position. Malic and citric acids have two hydroxyl groups, one of which is attached to a carboxyl group at the alpha position and the other to a carboxyl group at the beta position.

Uses of AHAs

AHAs are mostly known for their application in cosmetics and personal care products. These acids have numerous benefits for the skin. Due to their properties, they can combat signs of aging, fine lines, dark spots, and even acne; these properties include:

• Increasing skin thickness

• Improving the quality of elastic fibers

• Increasing collagen density

• Skin exfoliation

Also, alpha hydroxy acids are effective in reducing solar keratosis, roughness, and skin discoloration caused by sun exposure.

At concentrations of 4 to 10 percent, alpha hydroxy acids are available in creams or other products over the counter. While the pharmaceutical types have higher concentrations of over 20 percent and are only available with a prescription.

Mechanism of Action of Alpha Hydroxy Acids

Numerous studies have examined the mechanism of action of alpha hydroxy acids. The results of one study showed that the effects of alpha hydroxy acids when used topically are related to their chelating properties. This feature of alpha hydroxy acids leads to a reduction in the concentration of calcium ions in the epidermis and the release of calcium from cell adhesions. In fact, this results in the loss of calcium ions in desmosome cadherins (the main components of desmosomes that play an important role in maintaining intercellular adhesion) and adhesive connections. Consequently, disruption in cell adhesion occurs, leading to exfoliation. Additionally, the reduction in calcium can stimulate epidermal growth and delay cell differentiation.

Safety Evaluation of Using Alpha Hydroxy Acids in Cosmetics

Based on the report of the Cosmetic Ingredient Review (CIR) panel, which acts as a self-regulatory reference for the cosmetic industry to evaluate the safety of cosmetic ingredients, the use of products containing alpha hydroxy acids such as glycolic acid and lactic acid is safe under the following conditions:

• The concentration of AHA in the product is 10 percent or less.

• The final pH of the product is 3.5 or higher.

• The product formula is such that it protects the skin from severe sensitivity to sunlight, or the product usage guide advises consumers to protect their skin from sunlight during the day.

Possible Side Effects of Using Alpha Hydroxy Acids

Given the acidic nature of AHAs, a set of guidelines and safety precautions should be followed when using them. According to the U.S. Food and Drug Administration (FDA), some side effects resulting from the use of alpha hydroxy acids include:

• Skin burning

• Swelling

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Alpha Hydroxy Acids

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