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Is Dermatologic Usage of Coal Tar Carcinogenic?: A Review of the Literature

BACKGROUND Coal tar ointments have been used for decades in the treatment of various dermatoses, most notably eczema and psoriasis. Occupational exposure to coal tar poses an increased risk of developing cutaneous malignancies. The evidence of an increased risk of skin cancer in humans, as a result of dermatologic usage of tar, however, is conflicting. OBJECTIVE A consensus on the carcinogenicity of tar is sought. METHODS The existing literature (in vitro, animal, and human studies) on this subject is reviewed. RESULTS The carcinogenicity of coal tar has clearly been demonstrated by in vitro and animal studies, and appears to be potentiated by concomitant use of ultraviolet radiation. Systemic absorption of mutagens from topically applied tar has been demonstrated in humans. Epidemiologic studies in humans, however, have not definitively shown an increase in skin cancer with therapeutic use of tar. CONCLUSIONS Conclusive evidence for the carcinogenicity of tar used in dermatologic practice is lacking. Further controlled studies are necessary.