"Benzo[a]pyrene, C20H12, is a five-ring polycyclic aromatic hydrocarbon whose metabolites are mutagenic 
and highly carcinogenic. Benzo[a]pyrene is listed as a Group 1 carcinogen by the IARC. It belongs to a class of polycyclic aromatic compounds known as benzopyrenes, which consist of a benzene ring fused to a pyrene molecule. Benzo[a]pyrene is a product of incomplete combustion at temperatures between 300 and 600 °C (572 and 1,112 °F). Benzo[a]pyrene was determined in 1933 to be the component of coal tar responsible for the first recognized occupation-associated cancers, the sooty warts (cancers of the scrotum) suffered by chimney sweeps in 18th century England. In the 19th century, high incidences of skin cancers were noted among fuel industry workers. By the early 20th century, the toxicity of benzo[a]pyrene was demonstrated when malignant skin tumors were produced in laboratory animals by repeatedly painting them with coal tar. When the body's metabolism attempts to remove Benzo[a]pyrene by converting into a water soluble compound for easier excretion. The resulting diol epoxide, however, reacts with and binds to DNA resulting in mutations which can lead to cancer."