It is true that smoking causes cancer. It is a fact recognized worldwide that smoking causes cancer, and the World Health Organization has designated cigarettes as a class I carcinogen. China is a country with high incidence of lung cancer. According to statistics, the probability of smokers suffering from lung cancer is three to four times higher than that of non-smokers, and the probability of long-term smokers suffering from lung cancer is even higher. In addition to lung cancer, smoking also induces oral cancer, laryngeal cancer, esophageal cancer, cervical cancer, breast cancer, liver cancer and many other cancers. Tobacco combustion process, will release a variety of harmful substances, on the one hand, will damage the lung function, on the other hand, these harmful substances in a variety of carcinogenic or cancer-promoting substances, such as benzo(a)pyrene, cadmium, arsenic and so on. Long-term smoking in the human body will make the cells in the organism undergo abnormal DNA damage, gene mutation, etc., which will eventually lead to the occurrence of cancer. In addition to causing cancer, long-term smoking will also damage blood vessels, leading to atherosclerosis, cardiovascular and cerebrovascular disease incidence increases. This shows the health hazards of smoking, and smokers are advised to quit smoking as soon as possible under the guidance of a doctor.