This page of the Report on Carcinogens by the National Institutes of Health (NIH) summarizes the research findings on coal tars. Coal tars and coal-tar pitches are known to be human carcinogens, based on sufficient evidence of carcinogenicity from studies in humans.
In addition to its use in industry, coal tar preparations have been used for many years to treat various skin conditions, such as eczema, psoriasis, seborrheic dermatitis, and dandruff. Both prescription and nonprescription preparations are available and include cleansing bars, creams, gels, lotions, ointments, shampoos, and other topical solutions and suspensions. Coal tar is also registered as an active ingredient in pesticides with the U.S. Environmental Protection Agency (EPA).
The primary routes of potential human exposure to coal tars and coal-tar products are inhalation, ingestion, and dermal contact. The general population may be exposed to coal tar through its use in treating skin disorders. It has been estimated that nearly 2% of the United States population is affected by psoriasis, one of the conditions for which coal-tar ointments (containing 1% to 10% coal tar) are prescribed (IARC 1985). Others may be exposed through the use of coal-tar shampoos to treat dandruff or coal-tar ointments to treat eczema. The general population may also be exposed to coal tars pres-ent as environmental contaminants.
For more on the carcinogenicity of coal-tar pitch, see this paper from the IARC (International Agency for Research on Cancer) and this IARC summary of the data concerning the carcinogenicity of coal tar.