There is a controversial discussion of the carcinogenic action of coal tar used as a therapeutic agent in dermatologic practice. The carcinogen benzo(a)pyrene is present in most coal tar preparations, and it is a potent inducer of the aryl hydrocarbon hydroxylase activity in liver and skin after topical application. The formation of the most reactive metabolite of benzo(a)pyrene is catalyzed by aryl hydrocarbon hydroxylase hydroxylase. Topically used coal tar alters the mutagenicity of the urine indicating a systemic effect. These experimental data recommend to be very cautious in using coal tar as a therapeutic agent although there are only a few case reports on tumors after treatment with coal tar.
