Pyridoxine hydrochloride (vitamin B6) in oral doses of 500 mg daily induced blackening of the growing hairs of the scalp of an 18-year-old girl with homocystinuria. The specific periods of pyridoxine intake were registered on the previously blond scalp hair as distinct black bands. Microscopically the hair cortex in the dark bands showed an increased number of melanin granules. We have labeled this unique color phenomenon melanotrichia. It is postulated that the observed melanotrichia resulted from the reduction in tyrosinase inhibitory levels of homocysteine.
Shelley WB, Rawnsley HM, Morrow G. Pyridoxine-Dependent Hair Pigmentation in Association With HomocystinuriaThe Induction of Melanotrichia. Arch Dermatol. 1972;106(2):228-230. doi:10.1001/archderm.1972.01620110060014