Smoking Cigarettes contain more than 1,400 ingredients, and there are more than 40 kinds of carcinogenic substances in the smoke produced by smoking, and more than 10 kinds of substances that can promote the development of cancer, among which the most harmful to human beings are nicotine, CO, tar and many other metal compounds. Numerous epidemiological studies have demonstrated the close relationship between smoking and lung cancer, and the incidence and mortality of lung cancer continue to rise as a result of smoking. More than 80% of deaths from lung cancer are caused by smoking, including passive smoking. The mortality rate of lung cancer in male smokers is 8-20 times higher than that of nonsmokers. Passive smoking in women also predisposes to lung cancer, and the current increase in passive smokers in women is associated with an increased risk of lung cancer. The incidence rates of smokers and nonsmokers are only gradually approaching after about 15 years of quitting smoking. 2.Environmental factors Atmospheric and environmental pollution is another risk factor for the occurrence of lung cancer. A foreign study confirmed that serious air pollution can lead to a high incidence of lung cancer, and the incidence of lung cancer is significantly higher in cities than in villages, with incidence rates of 4-9% and 1-3% respectively. The harmful emissions from automobile exhaust, industrial processes, asbestos, radioactive isotopes, aromatic compounds, rubber and plastic manufacturing in cities lead to more serious air pollution than in the countryside. In addition, the fuel and fumes used in cooking are also risk factors for the development of lung cancer in women, and the combustion products of fuel contain many carcinogenic substances. It is recommended that cooking should be done in a well-ventilated kitchen.