Succinic Acid

Succinic acid is a dicarboxylic acid used in leave-on products (often ~0.5–2%) for mild keratolytic/anti-acne effects, and as an acidifier; at functional, low pH it can sting compromised or eczematous skin similar to other low-strength acids. Human patch-test data generally suggest low irritation at typical cosmetic levels, but clinical experience shows occasional burning/erythema in reactive individuals and with cumulative use alongside other actives, so I rate it mild rather than “gentle” for high-sensitivity populations. Safety Notes: In commercial skincare, succinic acid is most often seen as a minor supporting acid/pH adjuster or antimicrobial/deodorizing adjunct in leave-on and rinse-off formulas around ~0.05–0.5%, with the lowest marketed uses appearing near ~0.05% in multi-acid or preservative-boosting systems. High-strength consumer products (typically acne/blemish leave-on serums, spot treatments, or acid gels) are marketed in the ~1–2% range, with a small number of specialty/high-strength OTC products reaching about 5% succinic acid. There is no specific EU/FDA maximum for succinic acid as a cosmetic ingredient; practical upper limits are mainly driven by irritation risk, solubility, and pH/stability constraints, especially for leave-on products.