The relationship of pKa and acute skin irritation in man.

The relationship between pKa and skin irritation in man is studied for a homologous series of benzoic acid derivatives, which permeate through human skin at comparable rates (15-88 micrograms/cm2/hr). Skin irritation and pKa are correlated for pKa less than or equal to 4. Laser Doppler velocimetric assessment of skin blood flow, color meter readings, erythema, edema, and the primary irritation index are all linearly correlated and related to pKa; erythema at 24 hr appears to be the most sensitive parameter to variation in pKa when pKa less than or equal to 4.