Glycolic acid (AHA)

Also known as: alpha hydroxy acid, AHA, hydroxyacetic acid

Glycolic acid is the smallest and most used alpha hydroxy acid, sold in leave-on products around 5 to 10% and used in professional peels at 20 to 70%. Randomized trial evidence supports professional peels for acne and shows that even low-strength daily creams modestly improve sun-damaged skin. The honest picture: peels have decent trial support, while the dramatic resurfacing claims made for low-percentage home products rest on evidence showing modest, gradual change.

How it works

Glycolic acid loosens the bonds holding dead cells in the outermost skin layer, speeding their shedding and revealing newer skin. At higher concentrations and longer contact times it reaches deeper, triggering a wound-repair response that increases skin thickness, collagen, and hyaluronic acid in the dermis.

What the evidence says, claim by claim

These are the results measured in studies, not the results shown in ads. Where the research is weak, the grade says so.

For acne

Moderate evidence

A randomized, double-blind, placebo-controlled split-face trial in 26 patients found five 40% glycolic acid peels at 2-week intervals significantly reduced acne lesions versus placebo, working better on blackheads and whiteheads than inflamed lesions. A 2018 systematic review of 12 RCTs (387 participants) found chemical peels including glycolic acid similarly effective for mild-to-moderate acne, but rated the trial quality very low to moderate.

Randomized trials support this use, but they are few, small, or short. The effect is probably real. The size of it is less certain.

Clinical evaluation of glycolic acid chemical peeling in patients with acne vulgaris: a randomized, double-blind, placebo-controlled, split-face comparative study (Dermatologic Surgery, 2014; RCT)
Chemical peels for acne vulgaris: a systematic review of randomised controlled trials (BMJ Open, 2018; systematic-review)

For wrinkles and fine lines

Limited evidence

In a double-blind, vehicle-controlled trial of 74 women aged 40 to 70, 8% glycolic acid cream was modestly useful against signs of photodamage over 22 weeks, a finding the authors themselves phrased cautiously. Marketing for home glycolic products implies peel-level resurfacing; the controlled data show small improvements in fine lines at OTC strengths.

Only small, short, or lower-quality studies exist. Treat marketing claims about this use with caution.

Topical 8% glycolic acid and 8% L-lactic acid creams for the treatment of photodamaged skin. A double-blind vehicle-controlled clinical trial (Archives of Dermatology, 1996; RCT)

For dullness and texture

Moderate evidence

Texture smoothing is glycolic acid's most reliable effect. A controlled forearm study applying 25% AHA lotion for 6 months found about a 25% increase in skin thickness with improved elastic fiber quality and collagen density versus placebo, and the 8% cream RCT found improvement in overall photodamage scores driven largely by texture and roughness. Effects at typical 5 to 10% leave-on strengths are gradual, over 8 to 24 weeks.

Randomized trials support this use, but they are few, small, or short. The effect is probably real. The size of it is less certain.

Effects of alpha-hydroxy acids on photoaged skin: a pilot clinical, histologic, and ultrastructural study (Journal of the American Academy of Dermatology, 1996; RCT)
Topical 8% glycolic acid and 8% L-lactic acid creams for the treatment of photodamaged skin. A double-blind vehicle-controlled clinical trial (Archives of Dermatology, 1996; RCT)

Risks and what can go wrong

Stinging, redness, and flaking scale with concentration and pH. AHAs increase sun sensitivity (the FDA requires a sunburn-alert label), so daily sunscreen is not optional. Peels above 30% belong with professionals; misuse causes burns and post-inflammatory hyperpigmentation, a particular risk in darker skin. Low-strength topical use is generally considered acceptable in pregnancy.

The practical details

OTC leave-on products run 5 to 10% (higher with buffering); at-home peel pads reach 20 to 30%; professional peels use 20 to 70% with timed neutralization. Start 2 to 3 nights per week. Do not stack with retinoids or other exfoliants on the same night while adjusting. Results on texture appear within weeks; pigment and fine-line changes take months.