The relationships between cancer and exposure to chemicals have long been noted.

In 1761, Hill found that users of tobacco snuff had a high rate of nasal cancer.

Sir Percival Pott (1744–1788, English surgeon) observed, in 1775, that exposure to soot by chimney sweeps induced cancer of the scrotum (Pott, 1775).

Twenty years later, Sommering noted that cancer of the lip was often associated with pipe smoking.

163Rehn discovered in 1895 that bladder tumors occurred among workers in aniline dye factories. In the twentieth century, cancers induced by a variety of chemicals under different exposure conditions have been observed.

In 1915, Katsusaburo Yamagiwa and Koichi Ichikawa (1918) first succeeded in inducing experimental tumors in the skin of sensitive rabbit ears by applying coal tar (a complex mixture of chemicals) repeatedly to their skin every 2 or 3 days for a period of more than 100 days (Bishop, 1987).

Later in 1930, Earnest Kennaway demonstrated that dibenzanthracene, a chemical constituent of coal tar, was able to produce cancer in rats.

In 1933, Cook et al. (1933) also showed that benzo(a)pyrene (BaP) isolated from coal tar was carcinogenic in mouse skin.