Skip to main content

Exfoliating acids

Glycolic acid

Also listed as AHA, alpha-hydroxy acid

The smallest, most penetrating AHA. At 5-10% it smooths texture and evens tone over months, but raises sunburn risk while you use it.

Moderate evidenceTypical strength: 5-10% leave-on, pH 3.5+

What it is

Glycolic acid is the smallest alpha-hydroxy acid (AHA). It loosens the bonds between dead cells in the outer layer so they shed faster, which smooths and brightens skin; with long use at higher strengths it also thickens the epidermis and increases dermal collagen.

Strength depends on both percentage and pH: the lower the pH, the more free acid and the stronger (and more irritating) the effect. The US cosmetic ingredient safety panel considers AHAs safe in consumer products up to 10% at pH 3.5 or higher; 20-70% peels belong in a clinic.

How strong is the evidence?

Moderate evidence

A 22-week double-blind trial in 74 women found 8% glycolic acid cream improved overall photodamage more than vehicle (76% vs 40% improved by at least one grade), and a 25% lotion thickened skin and raised collagen density in a biopsy study. Effects at consumer strengths are modest. A controlled study found 10% glycolic acid for 4 weeks made skin burn more easily in UV light.

What it's used for, checked

Rough texture and dullness

Holds up

Speeds shedding of dead surface cells; visible smoothing within weeks.

Sun damage and fine lines

Holds up

Modest improvement at 8% over about 5 months; larger effects at clinic peel strengths.

Dark spots and melasma

Mixed

Helps as an add-on and in peels; weaker alone than dedicated pigment treatments, and irritation can darken brown skin.

Acne and clogged pores

Mixed

Peels help acne in small trials; salicylic acid gets into oily pores better.

Works well with

  • Sunscreen — essential
  • A plain moisturizer

Don't combine with

  • Retinoids, other acids or benzoyl peroxide in the same session if your skin is sensitive
  • Waxing, laser or professional peels in the same week

Who should be careful

  • Use sunscreen daily while using it and for a week after stopping: in a controlled study, 10% glycolic acid made skin burn more easily, an effect that faded within a week.
  • Stinging, redness and peeling are common; stop if skin burns or cracks. Darker skin tones risk dark marks from irritation.
  • Don't use on broken, sunburned or eczema-flared skin.
  • Low-strength products are generally considered acceptable in pregnancy because little is absorbed.

The studies

Every citation is checked against its PubMed record.

  1. Topical 8% glycolic acid and 8% L-lactic acid creams for the treatment of photodamaged skin. A double-blind vehicle-controlled clinical trial.
    Stiller MJ, Bartolone J, Stern R, Smith S, Kollias N, Gillies R, et al. · Archives of Dermatology · 1996 · RCT

    74 women with photodamaged skin used 8% glycolic acid, 8% L-lactic acid or vehicle cream twice daily for 22 weeks; at least one grade of facial improvement was seen in 76%, 71% and 40% respectively. Lactic acid also improved mottled pigment and roughness on the forearms. Benefits were modest and the creams well tolerated.

  2. Effects of alpha-hydroxy acids on photoaged skin: a pilot clinical, histologic, and ultrastructural study.
    Ditre CM, Griffin TD, Murphy GF, Sueki H, Telegan B, Johnson WC, et al. · Journal of the American Academy of Dermatology · 1996 · Pilot controlled study

    Lotions with 25% glycolic, lactic or citric acid applied to one forearm versus placebo on the other for about 6 months increased skin thickness by about 25%, with denser collagen and better elastic fibres on biopsy.

  3. Topical glycolic acid enhances photodamage by ultraviolet light.
    Kaidbey K, Sutherland B, Bennett P, Wamer WG, Barton C, Dennis D, et al. · Photodermatology, Photoimmunology & Photomedicine · 2003 · RCT

    In 29 adults, 4 weeks of 10% glycolic acid (pH 3.5) increased UV-induced sunburn cells and lowered the dose of UV needed to cause redness versus placebo; the effect was gone a week after stopping.

  4. Applications of hydroxy acids: classification, mechanisms, and photoactivity.
    Kornhauser A, Coelho SG, Hearing VJ · Clinical, Cosmetic and Investigational Dermatology · 2010 · Review

    Reviews alpha-hydroxy, beta-hydroxy and polyhydroxy acids, their uses for photoaging, acne and pigmentation, and their effects on sun sensitivity, noting that their mechanisms of action still need clarification.