Analysis of para-phenylenediamine allergic patients in relation to strength of patch test reaction

Despite having a positive patch test reaction to para-phenylenediamine (PPD), some patients continue to dye their hair, while others are forced to give up or abandon this practice. This difference in patient behaviour could be due to the degree of sensitization.

To establish whether the ability to continue dyeing hair in PPD allergic patients is related to the strength of patch test reaction. To note differences in other clinical features in relation to the strength of patch test reaction.

We analysed retrospectively the patch test records of 400 sequential PPD-positive patients for the strength of patch test reaction (+, ++, +++) and different clinical features. Data were analysed using Cochran-Mantel-Haenszel chi2 tests.

There was a strong linear relationship between the strength of patch test reaction and continuation with hair dyeing. Patients were more likely to report a history of hair dye reaction with increasing strength of patch test reaction. There was no difference in strength of patch test reaction in relation to age, site of rash, occupation (hairdressing) or history of atopic eczema. Overall concomitant reactivity with related aromatic amine allergens (benzocaine, N-isopropyl-N-phenyl-para-phenylenediamine, para-aminobenzoic acid) was infrequent.

Patients with stronger patch test reactions (++, +++) are more likely to have a clear history of reacting to hair dye and are less likely to still be dyeing their hair.