# Exfoliating acids (AHA and BHA)

> Source: https://thecastindex.com/beauty/ingredients/exfoliating-acids — updated 2026-09-25

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.

- Also on labels as: Glycolic acid, Lactic acid, Mandelic acid, Salicylic acid, Betaine salicylate, AHA, BHA
- Type: Chemical exfoliant

## 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

1. Start two or three times a week, usually in the evening
2. Do not use on broken, sunburnt or freshly shaved skin
3. 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.

## Products in the catalogue that list it

- [The Ordinary Glycolic Acid 7% Exfoliating Toner](https://thecastindex.com/beauty/the-ordinary-glycolic-acid-7-exfoliating-toner)
- [COSRX Low pH Good Morning Gel Cleanser](https://thecastindex.com/beauty/cosrx-low-ph-good-morning-gel-cleanser)

## Questions

### 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.

## Sources

- [DermNet — Salicylic acid](https://dermnetnz.org/topics/salicylic-acid)
- [DermNet — Chemical peels](https://dermnetnz.org/topics/chemical-peels)
- [American Academy of Dermatology — Understand sunscreen labels](https://www.aad.org/public/everyday-care/sun-protection/shade-clothing-sunscreen/understand-sunscreen-labels)

General information, not medical advice.