What is the difference between AHA and BHA?

AHAs are water-soluble and work on the skin’s surface; BHA (salicylic acid) is oil-soluble and can work inside pores, which is why it is favoured for oily and blemish-prone skin.

How often should I exfoliate with acids?

Start two or three times a week and adjust to your skin. Daily use suits only some formulas and skin types.

Ingredient library / Chemical exfoliant

Exfoliating acids (AHA and BHA).

Also on labels as: Glycolic acid · Lactic acid · Mandelic acid · Salicylic acid · Betaine salicylate · AHA · BHA

Edited by Kaiser Khan · Updated 25 September 2026 · Editorial policy

Quick answer

What is exfoliating acids (aha and bha)?

Exfoliating acids loosen the bonds between dead skin cells so they shed more evenly. Alpha hydroxy acids (AHAs) such as glycolic and lactic acid work on the surface for smoother, brighter-looking skin; beta hydroxy acid (BHA), salicylic acid, is oil-soluble and works inside pores, which suits oily and blemish-prone skin.

What it does

Smooths the look of rough texture and dullness (AHAs)
Helps clear congested pores and blackheads (BHA)
Can make skin more sensitive to the sun

Who it suits

AHAs: dull, rough or uneven-looking skin. BHA: oily, congested or blemish-prone skin. Sensitive skin should start slowly or choose gentler forms.

How to use it

Start two or three times a week, usually in the evening
Do not use on broken, sunburnt or freshly shaved skin
Wear sunscreen daily — AHAs increase sun sensitivity

Take care

Over-use causes redness, stinging and a damaged barrier
Avoid the same night as retinoids until skin tolerates both
If pregnant or breastfeeding, check leave-on acids with a pharmacist

What it pairs with

Follow with a ceramide or hyaluronic-acid moisturiser. Keep retinoids and strong vitamin C for different nights or times.

General information, not medical advice. For a skin condition, pregnancy or persistent irritation, speak to a pharmacist, GP or dermatologist.

In the catalogue

Products listing exfoliating acids (aha and bha).

Named in each brand’s own listing

The Ordinary · Skin prep

Glycolic Acid 7% Exfoliating Toner

An AHA texture step for evenings when skin is not compromised — follow the brand’s patch-test and SPF guidance; not a clinical treatment.

Read the guide ↗

COSRX · Skin prep

Low pH Good Morning Gel Cleanser

A low-pH morning cleanse that clears oil without leaving skin tight before sunscreen and base.

Read the guide ↗

Read further

Sources.

Exfoliating acids (AHA and BHA), answered

What is the difference between AHA and BHA?: AHAs are water-soluble and work on the skin’s surface; BHA (salicylic acid) is oil-soluble and can work inside pores, which is why it is favoured for oily and blemish-prone skin.
How often should I exfoliate with acids?: Start two or three times a week and adjust to your skin. Daily use suits only some formulas and skin types.