 In the 18th century a scrotal cancer of chimney sweepers, the chimney sweeps' carcinoma, was already known to be connected to soot.Benzo["a"]pyrene (B"a"P) is a polycyclic aromatic hydrocarbon found in coal tar with the formula C20H12.The compound is one of the benzopyrenes, formed by a benzene ring fused to pyrene, and is the result of incomplete combustion at temperatures between and .