Glycolic acid is the second most used member of the so-called alpha-hydroxy acids (AHAs) (the first being lactic acid), a group of organic acids that are used in skincare for their powerful exfoliating effects.
Glycolic acid, similar to the other AHAs, works by dissolving the keratine bridges between dead skin cells. This makes it easier for the cells to be shed, leaving smoother, younger-looking skin. Glycolic acid can be found naturally in sugarcane and has the smallest molecule among all the AHAs, making it the acid that penetrates the skin the easiest.
It also has an additional benefit: it has been shown in studies that the regular application of glycolic acid peels may boost the production of collagen and hyaluronic acid in the skin, resulting in mild anti-wrinkle activity.
The application of glycolic acid to the skin produces different results depending on the concentration used and the length of application. At concentrations below 2%, it is added to leave-on products to soften the uppermost layers of the stratum corneum and for its anti-inflammatory properties.
In medium-strength products (concentrations of 10-20%) it acts as a gentle chemical peel that can be used to treat acne, normalize keratinization, and decrease epidermal thickness. At concentrations above 20% (sometimes even up to 70% or more) it can be used as a strong chemical peel treatment that may only be left on the skin for a few minutes, after which it has to be neutralized (otherwise it may cause irritation and burning).
Regular application of glycolic acid offers several benefits: it increases skin cell turnover, which is beneficial for problems like acne and rosacea, decreases inflammation, and loosens dead skin cells from pores. AHA peels can improve the appearance of pigmentation issues such as melasma, acne scars, and post-inflammatory hyperpigmentation.
Glycolic acid peels are safe to use even during pregnancy and breastfeeding. The skin may be more sun-sensitive for several days after the peel.
Glycolic acid has been found to be more invasive than lactic acid, but with the added benefit of collagen-boosting activity.
The difference between glycolic acid and salicylic acid is that salicylic acid is a beta-hydroxy acid with a slightly different mechanism of action for its exfoliant activity. Unlike glycolic acid, salicylic acid is not suitable to use during pregnancy and breastfeeding.
A commonly asked question is whether or not glycolic acid can be used together with other skincare superstars such as retinol. The answer is yes, but only in carefully formulated amounts. Retinol can also increase the skin’s cell turnover rate, so these two agents combined in high concentrations may cause irritation, redness, and stinging. It has been shown, however, that in properly formulated skincare products the combination may be beneficial.