Ingredients

Alpha hydroxy acids

Alpha hydroxy acids — glycolic, lactic, mandelic, citric, tartaric, malic — are a family of small water-soluble organic acids used in cosmetic skincare for their exfoliating and humectant properties. Their cosmetic use is regulated under Annex III of EU cosmetic law.

At a glance

INCI names

Glycolic Acid; Lactic Acid; Mandelic Acid; Citric Acid; Tartaric Acid; Malic Acid; and the corresponding salts (sodium lactate, etc.)

Chemical class

Alpha hydroxy carboxylic acids (one hydroxyl group on the carbon alpha to the carboxyl)

Regulatory class

Cosmetic ingredients, with conditions for glycolic and lactic acid in Annex III of Regulation (EC) No 1223/2009 following SCCS opinion (Commission Regulation amending Annex III adopted in 2023, applicable from 2024)

Cosmetic function

Buffering; humectant; skin conditioning; exfoliating (depending on the species and concentration)

What they are

Alpha hydroxy acids (AHAs) are small organic acids characterised by a hydroxyl group on the carbon adjacent to the carboxyl group. Glycolic acid is the smallest (two carbons); lactic acid is three carbons; mandelic acid carries a phenyl group; citric acid has three carboxyl groups. In a cosmetic context, the most prominent species are glycolic and lactic acid, with mandelic acid sometimes used for its slower penetration profile attributed to its larger molecular size.

How they are used in parapharmacy products

AHAs are used in leave-on facial products marketed for textural and tone-related concerns, in rinse-off cleansers and masks, and at lower concentrations as buffering agents and humectants in many product types. Cosmetic-grade products containing AHAs as labelled actives typically use concentrations in the range of a few per cent up to, historically, around 10%. Higher-concentration "chemical peels" used by professionals are a separate use category subject to different rules.

Regulatory status

Glycolic acid and lactic acid are listed in Annex III of Regulation (EC) No 1223/2009 with conditions of use (maximum concentration, minimum pH, required warnings) following SCCS opinions on these substances. The European Commission amended Annex III in 2023 by Commission Regulation (EU) 2023/1490 to introduce specific conditions for glycolic acid and lactic acid in leave-on and rinse-off products, applicable from 2024; consult the consolidated EUR-Lex text for the current detail.

Cosmetic products containing AHAs above specified concentrations or below specified pH thresholds are required to carry sun-protection warnings, on the basis that AHA exfoliation can transiently increase skin photosensitivity. The text of the required warning is set out in Annex III.

Evidence summary

The cosmetic effects of AHAs at the concentrations and conditions permitted in EU finished products are best characterised as well-established for short-term effects on skin texture and superficial pigmentation. The mechanism — disruption of corneocyte cohesion in the lower stratum corneum and a stimulation of cell turnover — is described in the dermatological literature. The clinical effect depends on the species, the concentration, the formulation pH and the population studied. Cosmetic claims must comply with Regulation 655/2013 and must not present the product as treating a disease.

Safety and known considerations

Topical AHAs cause concentration-dependent and pH-dependent local irritation: stinging, erythema, dryness. The required warning on sun protection reflects the increased sensitivity of freshly exfoliated skin to UV exposure. Use of AHAs in combination with other exfoliants (salicylic acid, retinoids) increases the risk of cumulative irritation. AHAs are unsuitable for use on damaged or inflamed skin; cosmetic-product labelling must communicate any restriction in this regard.

Last reviewed: May 2026.