A carcinogen is any substance or agent that produces or induces the development of cancer. Carcinogens are known to affect and initiate metabolic processes at the level of cellular DNA.

Cancer accounts for slightly over 20% of all deaths each year. It is estimated that one out of every four Americans will develop cancer eventually and that six out of 10 in this group will die from the disease itself or complications arising from the disease. Half of all cancer deaths occur before the age of 65. Among women between 30 and 40 and children between three and 14, cancer is the leading cause of death next to accidents. It is the most frequent cause of death among Americans under 35 years of age.

The testing of chemicals as cancer-producing agents began with the observation of Sir Percival Pott in 1775 that scrotal cancer in young chimney sweeps resulted from the lodgement of soot in the...