P-Anisic Acid

P-Anisic Acid (4-methoxybenzoic acid) is primarily used as a preservative/antimicrobial or pH-adjusting support ingredient, typically at low concentrations (often ~0.1–0.5%). As a weak aromatic acid, it can sting or irritate compromised barriers (eczema, post-procedure skin) especially in leave-on products or when combined with other acids, but it is generally well tolerated by most users at typical use levels. Given documented low-to-moderate irritation potential typical of organic acids and the need to err on safety for highly reactive patients, a mild irritancy score is appropriate. Safety Notes: P-Anisic Acid is most commonly encountered in consumer skincare as part of preservative systems (often paired with organic acids/glycols), where it is typically used at low levels around ~0.05–0.3% in both leave-on and rinse-off products; the lowest market-seen usage is about 0.02% as a supporting antimicrobial/booster. High-strength OTC formulations (e.g., “preservative-free” natural brands relying on multi-acid preservation or deodorant/toner-style products) can reach ~0.5–1.0% to achieve broad antimicrobial support, with practical upper limits driven by pH/solubility and irritation risk rather than a specific EU/FDA concentration cap.