Cutaneous penetration of some hairdyes in the hairless rat

The cutaneous penetration of certain number of oxidation dyestuffs for hair [p-aminophenol, 2,4-diaminoanisole, 2,4-diaminophenoxyethanol, resorcinol, 3-acetylamino-2,6-dimethylphenol and the indamine: N-(4'-hydroxyphenyl)-3-amino-6-methylbenzoquinoneimine], either alone or when formulated with other dyestuffs, and under various experimental conditions, has been evaluated in the hairless rat using C14 labeled molecules. It has been found that: Dyestuffs having indamine structures, formed by oxidation of their precursors (bases, couplers), for all practical purposes do not cross the cutaneous barrier. No fixation of those dyestuffs investigated (resorcinol, 2,4-diaminoanisole, 2,4-diaminophenoxyethanol) which do pass through the cutaneous barrier is found in either liver or thyroid of the experimental animals, 4 days after their topical application. The amount of the hairdye 3-acetylamino-2,6-dimethylphenol which penetrates the cutaneous barrier is constant for quantities of hairdye solution greater than or equal to 20 mg/cm2 of skin. The type and composition of the excipient used in the formulation of hairdyes plays an important role in their penetration.