AHA (Alpha Hydroxy Acids) Explained

Glycolic acid · Lactic acid · Mandelic acid

AHAs are a group of exfoliating acids (glycolic, lactic, mandelic) that work on surface texture, depending on strength and formula. Evidence varies by formula and concern.

Evidence: strong

Label names (INCI): Glycolic Acid, Lactic Acid, Mandelic Acid, Malic Acid, Citric Acid

Written by the Oliareen editorial teamDermatologist review: pendingLast updated: 6 November 2026How we write

Myth vs fact

Myth: Everyone needs to exfoliate with acids.
Fact: No. Skin sheds dead cells on its own. AHAs are optional; they can irritate and make skin more sun-sensitive, so daily sunscreen is a must if you use them.

What it is

AHAs dissolve in water and work on the top layer of skin. Labels list Glycolic, Lactic, Mandelic, Malic or Citric Acid. Glycolic is the smallest molecule; mandelic is larger and usually works more slowly.

What it does

It loosens the bonds between dead cells, so skin can look smoother. Some studies found better tone and fine lines after months of regular use. Results depend on strength, pH and the whole formula.

Often discussed for

This doesn't mean everyone with these needs it.

Concerns

Skin types

How to approach it

It comes in toners, serums and cleansers. Many people start once or twice a week. Follow the product's directions rather than chasing percentages or pH, and never do home-made acid peels.

Morning or evening

Usually at night. Avoid using it on the same night as a retinoid, BHA, pure vitamin C or benzoyl peroxide. Sunscreen the next day is essential.

If you're new to it

Start one new active at a time and give it at least two to four weeks before adding another. Patch test first: a little on the side of the jaw or behind the ear for a few days. Keep the rest of the routine simple: a gentle cleanser, a moisturiser and sunscreen by day.

General education, not a diagnosis or treatment plan.

Works well with

Examples of common pairings, not guaranteed combinations.

Use carefully with

Stacking several actives raises the risk of irritation. If you're on any prescribed medicine, ask your doctor before adding an active.

Retinoids (in the same session)
BHA (salicylic acid) (in the same session)
Pure vitamin C (L-ascorbic acid) (in the same session)
Benzoyl peroxide
Photosensitising — mandatory SPF
Stinging, over-exfoliation
Pregnancy: glycolic/lactic <=10% acceptable

Possible reactions

A few seconds of mild tingling or a little dryness can happen at first. Stop if burning doesn't settle, or if a red rash, itching, swelling or peeling keeps getting worse. Swelling of the face, lips or eyes, or trouble breathing, needs urgent medical care.

When to see a doctor

Evidence and timing

Evidence: Evidence: strong
Time to see a change (weeks): 1-2 glow; 12-22 tone/lines

Evidence comes from studies of specific formulas and strengths. Your product may behave differently.

Questions people ask

What's the difference between AHA and BHA?

AHAs dissolve in water and work on the surface. BHA (salicylic acid) dissolves in oil and gets into pores. Our exfoliation page explains more.

How often should I use it?

There's no fixed rule. Many people start once or twice a week and increase only if skin stays comfortable. Check the product's directions.

Is AHA okay in pregnancy?

Low-strength glycolic or lactic acid products are generally considered acceptable. Ask your doctor before peels or any new active.

Sources

Stiller MJ et al. Arch Dermatol 1996;132:631-6 (74 women, 22 wk, 8% GA/LA vs vehicle)
Kaidbey K et al. Photodermatol Photoimmunol Photomed 2003
Tang SC, Yang JH. Molecules 2018 AHA review (PMC5849239)