The relationship between pKa and skin irritation for a series of basic penetrants in man.

For a series of bases, which penetrate through human skin in vitro at similar rates (0.056-0.49 microM/cm2/hr), penetrant pKa is shown to correlate with erythema, edema, and color meter readings. As estimates of irritation, erythema, edema, and redness measurements are highly linearly correlated. For the selected series, irritation becomes significant for bases with a pKa greater than 8. The irritation potential of acids with pKa less than or equal to 4 has been previously reported; pKa appears highly predictive of acute skin irritation for acids and bases in man.