Unconsumed precursors and couplers after formation of oxidative hair dyes

Contact allergy to hair dye ingredients, especially precursors and couplers, is a well-known entity among consumers having hair colouring done at home or at a hairdresser. The aim of the present investigation was to estimate consumer exposure to some selected precursors (p-phenylenediamine, toluene-2,5-diamine) and couplers (3-aminophenol, 4-aminophenol, resorcinol) of oxidative hair dyes during and after hair dyeing. Concentrations of unconsumed precursors and couplers in 8 hair dye formulations for non-professional use were investigated, under the conditions reflecting hair dyeing. Oxidative hair dye formation in the absence of hair was investigated using 6 products, and 2 products were used for experimental hair dyeing. In both presence and absence of hair, significant amounts of unconsumed precursors and couplers remained in the hair dye formulations after final colour development. Thus, up to 1.1% p-phenylenediamine (PPD), 0.04% toluene-2,5-diamine, 0.02% 3-aminophenol and 0.02% resorcinol were found in the hair dye formulation after the required colour was developed. The consumers are thus exposed to precursors and couplers of oxidative hair dyes, both during and after hair dyeing, when the hair is washed. Furthermore, the consumers are also expected to be exposed to intermediates of oxidative hair dyes. The allergenic potential of oxidative hair dyes as well as the intermediates of these remains unknown.