[Pattern of contact sensitization to paraphenylenediamine and its detection in hair dyes]

One of the greatest challenges in occupational dermatology is the identification of chemical substances used by patients in their work in order to determine their allergenic potential. Numerous techniques have been described for the identification of allergenic compounds. These tests must be sensitive, specific, and safe. We describe a study to detect the presence of paraphenylenediamine (PPD) in hair dyes that are commercially available in Spain.

We undertook an experimental study involving qualitative and semiquantitative detection of PPD in hair dyes sold in Spain. The qualitative technique we used was a previously described colorimetric method involving dilution of the dye with isopropyl alcohol followed by addition of a reagent solution (1g of vanilla in 15 ml of isopropyl alcohol and 7.5 ml of hydrochloric acid). A quantitative study was then done in which the dye was extracted in 96% ethanol and subjected to 1-dimensional thin-layer chromatography.

A total of 15 brown and 12 blonde dyes were analyzed. PPD was identified in all of the brown dyes analyzed, irrespective of whether it was indicated (n = 12) or not (n = 3) in the composition. PPD was found in 6 of the 9 blonde dyes that indicated it in the composition and 2 of the 3 in which it was not indicated. Semiquantitative analysis by thin-layer chromatography revealed that the concentration of PPD in brown hair dyes (mean, 3%) was higher than in blonde dyes (mean, 0.1-0.3%).

The presence of PPD in hair dyes is related to the color of the dye. It is consistently present in darker dyes and at low levels in blonde dyes. This study highlights the clinical and epidemiological importance of identifying allergens in dermatology, particularly in occupational dermatology.