Caprylic Acid

Caprylic acid (octanoic acid) is a medium-chain fatty acid used as an emollient component, pH adjuster, or antimicrobial/solubilizing aid, typically at low percentages, but in leave-on products it can still sting or burn on compromised barriers. Clinically, fatty acids and surfactant-like lipids can be irritant on eczematous or post-procedure skin, and caprylic acid’s acidity and membrane-disruptive antimicrobial behavior increases that risk compared with inert emollients. Given real-world use in multi-ingredient routines and the heightened vulnerability of sensitive-skin populations, a moderate irritancy score is the safer benchmark-aligned assessment. Safety Notes: In commercial skincare, caprylic acid is most often used at very low levels (about 0.05–1%) as an emollient/co-emulsifier, pH-aiding fatty acid, or antimicrobial-supporting component in leave-on creams/lotions and rinse-off cleansers. Higher levels are mainly seen in consumer-available high-strength exfoliating/anti-acne blends and “acid” treatment products where caprylic acid is used as part of an AHA/BHA/FFA acid system or solvent-like fatty acid phase; these can reach roughly 10–20% in leave-on formulations, with rinse-off products typically trending lower due to irritation and sensorial constraints. Caprylic acid is not subject to a specific EU/FDA max concentration limit as a standalone cosmetic ingredient, but practical upper use levels are constrained by skin tolerance, odor, and formulation stability.