AHA vs BHA: how exfoliating acids show up on a label

Two families of exfoliating acid

The FDA defines alpha hydroxy acids as organic acids with a hydroxyl group on the carbon next to the carboxylic acid group.¹ The most common in cosmetics are glycolic acid and lactic acid; others include citric acid, hydroxycaprylic acid and hydroxycapric acid.² Products containing AHAs cause exfoliation, the shedding of the skin's surface, and how much depends on the type and concentration of the AHA, its pH and the other ingredients in the product.²

The beta hydroxy acid most commonly used in cosmetics is salicylic acid. The FDA adds a caveat: from a chemist's perspective it is not a true BHA, but cosmetic companies often call it one, and so many consumers think of it as one. The FDA describes both AHAs and BHAs as exfoliants.³ CosIng also lists salicylic acid as a preservative.⁴

How they appear on a label

A name does not always say which family an acid belongs to, or whether it is there to exfoliate. CosIng, the EU's ingredient database, records these functions:

Only salicylic acid carries a function about dead skin cells: keratolytic, which CosIng defines as helping to eliminate the dead cells of the skin's outer layer. Glycolic and lactic acid are listed for buffering, defined as altering or maintaining a product's pH.⁹ That fits what the FDA says about AHAs: they are sometimes used for other purposes, such as adjusting the pH.²

BHA ingredients may also be listed as related substances such as sodium salicylate or willow extract.³ Esters such as Capryloyl Salicylic Acid are separate ingredients, which the US Cosmetic Ingredient Review panel assessed alongside salicylic acid.¹⁰ The checker's Exfoliating acids group collects AHAs, BHAs and PHAs, but leaves out citric, malic and tartaric acid because they are mostly used to adjust pH.

EU rules: limits for salicylic acid, none for AHAs

Salicylic acid has two entries in the EU Cosmetics Regulation. Annex III, entry 98, covers uses other than preserving, such as exfoliating, and sets maximums by product type. Annex V, entry 3, covers its use as a preservative.¹¹

Both entries exclude oral products and uses that could expose the lungs by inhalation, and neither allows salicylic acid in products for children under three; the preservative entry makes one exception, for its salts in shampoos. Entry 98's levels include any use of salicylic acid in the product.¹¹ The salicylic acid page covers the 2025 review of children's exposure.

Glycolic and lactic acid have no entry in any annex, and CosIng lists no restriction for either.¹¹⁵⁶ The EU's scientific committee of the time did suggest precautionary levels for both in 2000, compared in glycolic acid vs lactic acid, but those suggestions are not in the annexes.¹²¹¹

US guidance: a sunburn alert for AHAs

In January 2005 the FDA recommended that cosmetics containing an AHA and applied to the skin or lips carry a statement conveying this: "Sunburn Alert: This product contains an alpha hydroxy acid (AHA) that may increase your skin's sensitivity to the sun and particularly the possibility of sunburn. Use a sunscreen, wear protective clothing, and limit sun exposure while using this product and for a week afterwards." FDA guidance is a recommendation, not a legal requirement, and this one does not cover products that are also labelled to contain a sunscreen.¹

The FDA's own studies point the same way. After four weeks of applying an AHA cream, volunteers' sensitivity to UV-induced reddening rose by 18% and their sensitivity to UV-induced cell damage doubled on average. A week after stopping, researchers found no significant differences.²

For BHAs, the FDA's consumer page advises similar precautions to those for AHAs, including sun protection.³

Why pH and concentration matter, and why the label is silent

The US Cosmetic Ingredient Review panel's 1998 report found that the skin absorbs AHAs, and absorbs more the lower the pH. In clinical tests, irritation rose with AHA concentration at a given pH, and rose when the pH of a given concentration was lowered.¹³ The panel's conclusion pairs a maximum concentration with a minimum pH;¹ the figures are set out in glycolic acid vs lactic acid.

For salicylic acid, the panel found in 2003 that the data were not enough to set a concentration or a minimum pH at which no irritation would occur. It concluded they are safe as used when formulated to avoid irritation and increased sun sensitivity, or with directions for daily sun protection where that sensitivity is expected.¹⁰ Its 2025 amended assessment concluded that salicylic acid and 17 salicylates are safe in cosmetics in the present practices of use and concentration when formulated to be non-irritating and non-sensitising.¹⁴

None of this reaches the label. Under Article 19 of the EU regulation, the ingredient list runs in descending order of weight, and names below 1% may follow in any order.¹¹ The list gives no percentages and no pH, yet both shape how much an acid exfoliates.² Ingredient list order explains what position can and cannot show.

What to look for on the label

• Read each acid's full name. Glycolic, Lactic and Mandelic Acid are AHAs; Salicylic Acid is the usual BHA; Citric Acid is listed in CosIng for buffering and chelating, not exfoliating.⁸
• Look for the sunburn alert on US packs of AHA products. It is a recommendation, so its absence proves nothing.¹
• Check the position, remembering that below 1% the order is free.¹¹ How to read a cosmetic ingredient list covers the rest.
• Sort the whole list at once with the skincare ingredient checker, which marks names in its Exfoliating acids group.

A name says what is in a product, not how strongly it acts: concentration, pH and the rest of the formula decide that, and a label shows none of them.