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Glycolic acid

Glycolic acid in skincare: Exfoliant, keratolytic. What it does on skin, how strong the evidence behind the claim actually is, the concentrations in normal use, who reacts to it, and where it stands in pregnancy and sunlight. On a label it appears as Glycolic Acid.

Exfoliating acidsExfoliant, keratolyticEvidence: Strong

On the label: Glycolic Acid. Also called: AHA, alpha hydroxy acid, fruit acid.

This is an ingredient reference, not a diagnosis and not a treatment plan. It describes what substances are and what the published evidence supports; it does not tell you what your skin has or what to put on it. A rash that spreads, hurts, weeps, does not settle, or comes with feeling unwell is a reason to see a doctor or pharmacist, not to change serum.

What it is

The smallest of the alpha hydroxy acids, a two-carbon acid originally isolated from sugar cane and now made industrially. Its small size is the whole point: of the common AHAs it crosses the outer skin fastest, which makes it both the most effective and the most likely to sting. It is sold in cosmetic strengths for home use and in far higher strengths as a professional peel, and those two things behave nothing alike.

What it does on skin

It weakens the bonds holding dead cells together at the surface, so the outermost layer sheds more evenly instead of building up in patches. The visible result is a smoother, more even, more light-reflective surface within days. Over longer courses at higher strengths, studies also report changes deeper down — more ground substance and collagen in the dermis — which is the mechanism behind its use for fine lines and sun-damaged texture rather than just glow.

What the evidence is worth

Evidence: Strong

The surface effect is not in doubt: it is measurable, reproducible and quick. The deeper anti-ageing effect is supported by smaller studies, usually at peel strengths and over months, so a home toner is not the same intervention. Free acid at a low pH is what does the work, which is why two products with the same percentage on the front can perform very differently.

How it is used

Evening, on dry skin, starting two or three nights a week and building up only if nothing stings. A leave-on serum or toner at 5-10% is a normal consumer strength; anything much stronger belongs to a trained operator. Stop before waxing, threading or a laser appointment, and stop while skin is broken, sunburnt or already peeling.

Typical concentration in normal use: 5-10% in consumer leave-on products. That is a description of the market, not a recommendation, and it is not a dose.

Who reacts to it

Stinging in the first minute is common and usually settles. Persistent burning, tightness, shininess or new sensitivity to products that were fine last month means the barrier is over-exfoliated, and the fix is to stop for two weeks and use plain moisturiser. People with rosacea, eczema or a compromised barrier tolerate it poorly.

Pregnancy and breastfeeding

Generally considered fine

Topical AHAs are poorly absorbed and are generally treated as acceptable in pregnancy, unlike oral or high-strength professional peels. Skin is also more reactive in pregnancy, so this is a good time to use less rather than more, and to check with your midwife or clinician first.

Sunlight

More sun-sensitive

AHA use increases sensitivity to ultraviolet light and that sensitivity persists for about a week after you stop. Daily sunscreen is not an upsell here, it is part of the treatment: without it you undo the pigment benefit you were exfoliating for.

Rules and labelling

The Cosmetic Ingredient Review has concluded glycolic acid is safe for consumer products at concentrations up to 10% at a pH of 3.5 or above, and at higher concentrations only for brief professional use. Consumer products in the EU sit far below salon peel strength, and sun-protection wording is the standard expectation on an AHA label.

What it goes with, and what it does not

It pairs badly with a retinoid on the same night for most people — not because of a chemical conflict but because the irritation stacks. Alternate nights instead. It pairs well with a plain moisturiser applied ten minutes after, and with sunscreen the following morning, which is not optional.

One thing people get wrong

The myth is that the percentage on the front of the bottle tells you the strength. It does not. A 10% glycolic product buffered to pH 5 has far less free acid available than a 5% product at pH 3.5, so it does less. Percentage without pH is half a number, and the brand that gives you both is telling you more than the brand that shouts louder.

Sources: EU Cosmetics Regulation (EC) No 1223/2009 and its annexes, as published in the European Commission's CosIng database, for every statement about what is permitted, restricted or banned · opinions of the Scientific Committee on Consumer Safety (SCCS) and safety assessments of the Cosmetic Ingredient Review (CIR) for the concentration positions · standard dermatology reference material for mechanism, tolerability and contact-allergy patterns · checked 2026-09-06. Deep links are deliberately omitted where a stable public URL could not be confirmed.

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