Smoking is currently considered the most important risk factor for lung cancer. There are more than 3,000 chemicals in tobacco, including multi-chain aromatic hydrocarbon compounds (e.g. benzo(a)pyrene) and nitrosamines, which have strong carcinogenic activity. Multi-chain aromatic hydrocarbon compounds and nitrosamines can cause DNA damage to bronchial epithelial cells through various mechanisms, resulting in activation of oncogenes (e.g. Ras gene) and inactivation of oncogenes (e.g. p53, FHIT gene, etc.), which can lead to cell transformation and eventually carcinogenesis. 2.Atmospheric pollution The prevention of lung cancer requires improvement of atmospheric pollution. The incidence of lung cancer in many industrially developed countries is extremely high, and the incidence is higher in urban than rural areas, and higher in factories and mines than in residential areas. The main cause of lung cancer in this area is due to the pollution of the atmosphere by harmful substances such as benzo(a)pyrene carcinogenic hydrocarbons produced by the combustion of oil, coal and internal combustion engines and asphalt road dust in industrial and transportation developed areas. 3.Occupational relationship This is because some jobs must be exposed to radioactive substances such as radium, uranium and mustard gas, asbestos, petroleum, asphalt, coal tar, arsenic, chromium, nickel, copper, tin, and other carcinogenic substances every day, which are the causes of lung cancer, and people who work in this area should pay more attention to the prevention of lung cancer. 4. Chronic lung diseases Some people are not aware of the chronic lung diseases, which may also be the cause of lung cancer, such as pneumoconiosis, silicosis and tuberculosis. Once suffering from these lung diseases, the chance of developing lung cancer will be high. If you want to carry out lung cancer prevention, you should be alert to these diseases as well. Moreover, if you suffer from lung fiber scarring lesion or non-bronchial chronic inflammation will also slowly turn into lung cancer, which is also one of the causes of lung cancer. 5. Family environment The decoration materials of the house and the fumes from cooking contain many ulcer-causing substances, and passive smoking caused by smoking among family members can also pollute the small family environment. The cause of lung cancer in women may be related to the long-term inhalation of cooking fumes. 6.Genetic factors Family gathering, genetic susceptibility, lowered immune function, metabolic and endocrine dysfunction may also play an important role in the occurrence of lung cancer. Many studies have proved that genetic factors may play an important role in the population and/or individuals who are susceptible to environmental carcinogens.