Sensitization to p-phenylenediamine.

p-Phenylenediamine (PPD) from 0.2 mg to 1.6 mg in water or in petrolatum was applied as a patch test to 501 patients with different dermatoses, asthma, hay fever, and venereal diseases. Of these patients 10.6% reacted within the first five days indicating previous hypersensitivity and 14.4% between the sixth and the 16th day indicating the initiation of hypersensitivity to PPD by the patch application (flare-up). The reactions within the first five days were not correlated with the amount of PPD in the tests, but a statistically significant correlation was found between flare-ups and amount, so that the larger the amount of PPD the higher the frequency of flare-ups. About one half of both reactions occurred in patients with eczematous dermatitis.