Relative irritancy of free fatty acids of different chain length.

Free fatty acids of human skin surface lipids have previously been implicated in the pathogenesis of acne vulgaris because of their apparent irritant and comedogenic properties. Prior studies on the relative irritancy of free fatty acids revealed the saturated C8 to C14 fatty acids and a C18 dienoic unsaturated fatty acid (linoleic) to be most irritating. Saturated free fatty acids from C3 to C18, and unsaturated C18 free fatty acids were applied daily under occlusive patch tests to human skin until detectable erythema appeared. The most irritating fatty acids were C8 through C12. Of the unsaturated fatty acids tested, only linoleic acid produced irritation.