Cigarette causes lung cancer
Cigarette smoking is the single greatest risk factor for lung cancer. There is a significant "dose-response" relationship between the number of pack-years smoked and lung cancer risk; that is, the more a person smokes and the longer he or she smokes, the greater the risk for lung cancer.
How does cigarette smoking cause lung cancer? This question has not yet been answered definitively, but the toxic mix of chemicals found in tobacco smoke is the likely factor. Major chemicals in cigarette smoke that have been studied with respect to lung cancer include:
- polycyclic aromatic hydrocarbons (PAHs)
- nicotine by-products
- tobacco-specific nitrosamines (TSNAs)
- metals (e.g., nickel, cadmium)
- radioactive polonium 210 (210Po)
Types of Tobacco
The main commercially grown species of tobacco used in cigarette products in the United States, western Europe, and Japan is Nicotiana tabacum. Within this species, sub-types of tobacco include bright (Virginia, flue-cured), Burley, Maryland, and oriental (aromatic) tobaccos. Cigarettes made in the United Kingdom and Finland primarily use bright tobaccos. Both varieties of cigarettes, when ignited, create smoke particles containing nicotine. Such "mainstream" smoke particlesminus water and nicotineare the "tar" produced by burning cigarettes.
Cigarettes are made from sheets of reconstituted tobacco. Special solutions are used to keep the tobacco mixture intact, and chemicals known as humectants are added to maintain tobacco moisture. In addition, trade secret flavorants are included to make the product taste better during smoking. Such tobacco additives, when burned, may yield undesirable compounds. For example, the burning of licorice flavorant may produce chemicals known as polycyclic aromatic hydrocarbons (PAHs), and the burning of sugar may increase tar and nicotine in the smoke. Coumarin, a known cancer-causing substance in animals, has in the past been used as a tobacco additive. It is also likely that commercial tobaccos contain up to a few parts per million of the pesticides DDT and DDD, as well as the agricultural chemical maleic hydrazide.
Approximately 400 to 500 separate gaseous substances are present in the smoke of a nonfilter cigarette. The major elements of cigarette vapor include:
- carbon dioxide
- carbon monoxide
Other noteworthy substances include:
- nitrogen oxides
- hydrogen cyanide