Benzoic Acid

Benzoic acid is primarily used as a preservative/pH-adjusting agent, typically around ~0.1–0.5% in cosmetics, and can sting or irritate compromised or highly reactive skin—especially in leave-on products or at lower pH where the undissociated acid is more biologically active. Patch testing and real-world reports show occasional irritant reactions (and less commonly allergy), so while many tolerate it, sensitive/eczema-prone users can flare. Given patient-safety priorities and its acid-dependent irritation potential, it warrants a mild-but-not-negligible score. Safety Notes: In consumer skincare, benzoic acid is most often used as an acid-form preservative/antimicrobial and pH-supporting component, with low-end usage around ~0.05% in leave-on lotions/creams (often alongside sorbic acid or other preservative systems) where only a small boost is needed. Mainstream rinse-off and leave-on products commonly fall around 0.1–0.5%, while higher-strength OTC products (e.g., acne/body care or strongly acidified specialty formulas where benzoic acid contributes to antimicrobial performance and pH control) can reach about 1–2%. Higher levels are constrained by potential irritation and the need for sufficiently low pH to keep the acid in its effective, undissociated form, so very high percentages are uncommon outside specialty consumer formulations.