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Glycolic acid

Glycolic acid is the smallest alpha hydroxy acid (AHA) and the most studied exfoliating acid in skincare. It loosens the outermost layer of dead skin cells so they shed more evenly, and it makes skin more sensitive to the sun while it is in use.

At a glance

  • Evidence level A. Published research on the ingredient itself.
  • What it is. A water-soluble alpha hydroxy acid with two carbon atoms, the smallest in its class.
  • What it does. Surface exfoliation. Skin feels smoother and looks brighter in published studies of AHA formulas.
  • Caution. Increases sun sensitivity. Use sunscreen daily while using it and for a week afterwards.

What it is

Glycolic acid occurs naturally in sugar cane and some fruit; cosmetic grades are mostly made synthetically for purity. It belongs to the alpha hydroxy acids, a family that also includes lactic, citric and malic acids.

Two numbers set how a glycolic acid product behaves: concentration and pH. At a lower pH, more of the acid is in its free, active form. Two products with the same percentage can therefore act very differently, and a percentage on its own says little.

Lactic Acid/Glycolic Acid Copolymer is a separate ingredient: a polymer built from the two acids, with no free-acid action in a formula.

What it does in skincare

In the outer layer of skin, the stratum corneum, dead cells are held together by bonds that weaken naturally as the cells rise to the surface. Glycolic acid weakens that cohesion further, so cells detach more evenly. The visible result, in studies of AHA formulas, is skin that feels smoother and reflects light more evenly.

Glycolic acid appears in three kinds of product. Leave-on serums and toners at low strength, used daily or several times a week. Rinse-off cleansers, with short contact. Professional peels at higher strength, where concentration, pH and contact time are set by the practitioner. See chemical peels for how professional use differs.

Evidence

The studies below describe the ingredient itself.

Van Scott and Yu described in 1984 how alpha hydroxy acids reduce the cohesion between surface skin cells. That work is the basis for the category. A pilot study by Ditre and colleagues applied AHA lotions to sun-damaged skin over several months and reported changes in both the epidermis and the dermis, in a small number of participants.

The US Cosmetic Ingredient Review assessed glycolic and lactic acid in 1998. It concluded that they are safe in consumer products at up to 10% and a final pH of 3.5 or higher, when the product is formulated to avoid increasing sun sensitivity or its directions call for daily sun protection. Salon products were assessed separately, at higher strength with brief contact and thorough rinsing.

The sun sensitivity finding comes from a study published by Kaidbey and colleagues in 2003. Glycolic acid applied for several weeks increased the skin's sensitivity to ultraviolet light, measured as redness and sunburn cells. The effect had reversed a week after application stopped. FDA's labeling guidance for AHA cosmetics rests on this work.

Use and caution

Sun-sensitivity notice. FDA recommends this statement for cosmetics containing alpha hydroxy acids:

Sunburn Alert: This product contains an alpha hydroxy acid (AHA) that may increase your skin's sensitivity to the sun and particularly the possibility of sunburn. Use a sunscreen, wear protective clothing, and limit sun exposure while using this product and for a week afterwards.

More on using acids safely: acids and sun sensitivity.

  • Patch test a new acid product first. See patch testing and declared allergens.
  • Start with a few evenings a week and build up.
  • Mild tingling on application is common. Stinging that persists, or redness that stays, means stop.
  • Avoid the eye area and broken skin.
  • Do not layer several exfoliating products in the same routine without a professional's guidance.
  • Pause acids before waxing, and after a professional treatment until your practitioner clears them.

A run of small bumps in the first weeks of an acid is often attributed to "purging". What the term covers: the purging myth.

In Vegalab products

The Brightening NanoSerum sealed vial set lists glycolic acid as its second ingredient, after water, together with mandelic acid and lactic acid. The sun-sensitivity notice above applies to it.

References

  1. Van Scott EJ, Yu RJ. Hyperkeratinization, corneocyte cohesion, and alpha hydroxy acids. J Am Acad Dermatol. 1984;11(5 Pt 1):867-879.
  2. Ditre CM, Griffin TD, Murphy GF, et al. Effects of alpha-hydroxy acids on photoaged skin: a pilot clinical, histologic, and ultrastructural study. J Am Acad Dermatol. 1996;34(2 Pt 1):187-195.
  3. Cosmetic Ingredient Review. Final report on the safety assessment of glycolic acid, ammonium, calcium, potassium, and sodium glycolates, methyl, ethyl, propyl, and butyl glycolates, and lactic acid, ammonium, calcium, potassium, sodium, and TEA-lactates, methyl, ethyl, isopropyl, and butyl lactates, and lauryl, myristyl, and cetyl lactates. Int J Toxicol. 1998;17(Suppl 1):1-241.
  4. Kaidbey K, Sutherland B, Bennett P, et al. Topical glycolic acid enhances photodamage by ultraviolet light. Photodermatol Photoimmunol Photomed. 2003;19(1):21-27.
  5. US Food and Drug Administration. Guidance for Industry: Labeling for Topically Applied Cosmetic Products Containing Alpha Hydroxy Acids as Ingredients. January 2005.
  6. Kornhauser A, Coelho SG, Hearing VJ. Applications of hydroxy acids: classification, mechanisms, and photoactivity. Clin Cosmet Investig Dermatol. 2010;3:135-142.
  7. Tang SC, Yang JH. Dual effects of alpha-hydroxy acids on the skin. Molecules. 2018;23(4):863.
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