Sorbic Acid

Sorbic acid is an antimicrobial preservative typically used around ~0.1–0.3% (sometimes higher depending on pH), and it can sting and irritate, especially in leave-on products and on compromised barriers. Patch testing and clinical experience show it can provoke irritant reactions and occasional allergy in reactive/eczema-prone patients, so I score it as a moderate-risk preservative where patch testing is prudent. Safety Notes: In commercial skincare, sorbic acid is most often used as a preservative/acidifier at very low levels, with leave-on and rinse-off products commonly starting around ~0.01–0.05% when paired with other preservative systems. Higher-strength consumer-available formulations (e.g., “preservative-free”-leaning systems relying more heavily on sorbic acid, low-pH gels/toners, and some natural/organic emulsions) can reach ~0.2–0.6% to achieve antimicrobial support, though performance is pH-dependent and typically strongest in acidic formulas (often used alongside potassium sorbate and/or benzoic acid). This range reflects observed OTC market use; practical upper limits are usually driven by solubility, odor/sensory impact, and irritation risk rather than a single global maximum.