Mandelic Acid

Mandelic acid is an alpha-hydroxy acid (AHA) exfoliant typically used around 5–10% in leave-on products at an acidic pH, where it actively disrupts corneocyte cohesion and can sting or burn compromised skin. Although it is generally less irritating than glycolic acid due to its larger molecular size and slower penetration, clinical experience and patch-test data still show meaningful irritancy in sensitive skin (especially with eczema, barrier damage, or concurrent retinoids/other acids). Given its active, pH-dependent keratolytic action and the real-world risk of cumulative irritation in routines, it warrants a significant irritancy score. Safety Notes: In commercial consumer products, mandelic acid appears at very low levels (~0.2–1%) in gentle daily leave-on toners/serums and in multi-acid blends where it functions as a mild exfoliating/renewal support. The upper end of the OTC market is typically 10–20% in high-strength at-home chemical peel solutions and strong leave-on treatments marketed for periodic use; above this tends to be more common in professional-only peeling systems rather than general retail. Effective use is strongly pH-dependent (often ~pH 3–4 in leave-on products), and rinse-off cleansers may list mandelic acid but usually at lower effective exposure than leave-on formats.

Suitability