AHA, BHA and PHA: a guide to exfoliating acids in skincare
Glycolic, lactic, salicylic, gluconolactone – what the acids on your label are, how they differ and why the same acid can be an exfoliant in one product and just a pH adjuster in another.
Updated: 31 October 2026 · Reviewed by: Kamil Pyziak
What chemical exfoliation means
Exfoliating acids loosen the bonds that hold dead cells together in the outermost layer of the skin, so they shed more evenly. Unlike scrubs, they work without rubbing. How strongly they act depends mainly on the type of acid, its concentration and the pH of the product.
Those last two factors are not printed on the INCI list. That is why reading the label can tell you which acid is present, but not how strong the product is.
AHA: glycolic, lactic, mandelic
Alpha hydroxy acids (AHA) are water-soluble. The most common are Glycolic Acid (the smallest molecule), Lactic Acid and Mandelic Acid (a larger molecule, often described as working more gradually). Citric, malic and tartaric acids also belong to this family.
AHAs work on the skin surface. They are found in toners, serums, peels and body lotions. Products with AHAs can increase the skin’s sensitivity to the sun, so manufacturers usually recommend daily sun protection.
BHA: salicylic acid
In cosmetics, the beta hydroxy acid you will meet is Salicylic Acid. It is more oil-soluble than AHAs, which is why it is popular in products for oily and blemish-prone skin and in anti-dandruff shampoos.
In the EU, salicylic acid is regulated in two places: as a preservative (Annex V) and for other uses (Annex III), with maximum concentrations that depend on the product type and restrictions for products used on children under three. Related salts and esters, such as Sodium Salicylate, may appear on labels too.
PHA: gluconolactone and lactobionic acid
Polyhydroxy acids (PHA) such as Gluconolactone and Lactobionic Acid have larger molecules with several water-binding groups. They are often marketed for sensitive skin because they act more slowly at the surface, and they also behave as humectants.
“Gentler” is a relative description: tolerance is individual, and a strong formula with PHA can still irritate.
Same acid, different role
Citric acid near the end of a list is almost always there to adjust pH, not to exfoliate. Lactic acid may be paired with Sodium Lactate as a buffer. Salicylic acid in small amounts may be acting as a preservative.
A good rule of thumb: an acid that is meant to exfoliate is usually named on the front of the pack and appears higher on the list, often with instructions to use it only a few times a week.
Using acids sensibly
Introduce one acid product at a time, follow the manufacturer’s instructions and use sun protection during the day. Combining several strong exfoliants or using them together with other potentially irritating products increases the risk of irritation.
If you have a skin condition, are using prescription treatments or are pregnant, ask a doctor or pharmacist before starting a new exfoliating product.
What the label does not tell you
The INCI list will not show the percentage of acid or the product’s pH, both of which strongly affect how it works. Two serums listing glycolic acid can differ greatly in strength. When in doubt, look for information from the manufacturer and start slowly.