Percutaneous absorption of hair dyes: correlation with partition coefficients

A homologous series of hair dyes was selected for percutaneous absorption studies with excised human skin. The permeability constants obtained for the dyes were compared with octanol/water and skin membrane/water partition coefficients. The compounds examined were: p-phenylenediamine, o-phenylenediamine, 2-nitro-p-phenylenediamine, 2-amino-4-nitrophenol, 4-chloro-m-phenylenediamine, and 4-amino-2-nitrophenol. Skin absorption of the dyes was observed when they were applied in an aqueous solution. With one exception, the octanol/water partition coefficients were in the same rank order as the permeability constants. The determination of the partitioning of the hair dyes between water and either stratum corneum or epidermis was more complex. Preliminary stratum corneum/water partition studies resulted in values that were in the reverse order of skin permeation. When binding of the compounds to components of the membrane was saturated, the partition values more closely duplicated the rank order of permeability of the dyes. Prediction of percutaneous absorption of substances based on their partition coefficients may be confounded if these compounds are capable of binding to skin.