Tobacco Smoking
Tobacco contains about 4000 chemical compounds, most of which are proven carcinogenic. Polycyclic aromatic hydrocarbons and nitrosamines are the main cancer-causing agents are present in the tobacco smoke. Cessation of smoking can greatly reduce the chances of lung cancer each year. If a person quit smoking for 15 years, he will approach the risk of developing cancer as a non-smoker as damaged cells due to smoking will then replaced by the healthy cells.