The incidence of lung cancer is still increasing in many countries and has become the leading cause of cancer deaths. Currently, the incidence of lung cancer in China has taken the first place among various malignant tumors in major cities in China, and its mortality rate has exceeded the world average. At present, it is recognized that smoking is the most important factor leading to the development of lung cancer. Domestic data also show that 80% of lung cancer patients have a history of smoking, and about 3/4 of lung cancer patients have a history of heavy smoking. The harmful effects of cigarette smoking are not immediately apparent. The first British made cigarettes in 1881, and later spread to Europe and the United States, becoming a fashion. It was not until 1950, 70 years after the cigarette epidemic, when the incidence of lung cancer in the United Kingdom rose sharply and the incidence rates in the United States, Australia and Japan also rose, that people began to suspect that smoking and lung cancer might be related. In the future, countries have conducted studies and large-scale prospective population surveys, and found that smoking can cause cancer, and the possibility of cancer is closely related to the length of time smoking and how much smoking. The more you smoke, the earlier you start smoking, and the longer you smoke, the higher the risk of lung cancer. We should remember the three “20s”, those who have smoked for more than 20 years, those who started smoking under the age of 20, and those who smoke more than 20 cigarettes a day. Any one of the three “20s” is very likely to get lung cancer. In addition, some people are used to smoking one after another, a cigarette is too short to be thrown away, there are people who smoke very deep, most of the smoke is inhaled into the lungs, there are people with chronic bronchitis, but still “insist” on smoking, these behaviors are very harmful. However, we can encounter such situations in life: some people die of lung cancer even though they do not smoke, some people smoke for a long time without lung cancer, some people do not suffer from lung cancer during smoking, but suffer from lung cancer after quitting. This and so on, make people greatly confused. 1.Why do non-smokers die from lung cancer? Although smoking is the main cause of lung cancer, it is not the only cause. There are at least other related factors: occupational carcinogenic factors, air pollution, ionizing radiation, dietary factors, viral infections, fungal toxins, endocrine disorders, family genetics and so on. The occurrence of lung cancer is the result of a combination of factors. Non-smoking is not the same as no passive smoking. Non-smokers who smoke for more than 15 minutes a day are considered passive smokers. It has been found that if one person in a couple smokes heavily, the risk of lung cancer in the other person is greatly increased. This is because the content of carcinogenic agents in cigarette smoke is more than 50 times higher than that inhaled by the smoker himself. 2. Why some long-term smokers do not get lung cancer This is related to the fact that each person’s physique is different. The lung cancer-causing carcinogen in cigarette smoke is benzo(a)pyrene, which must be processed by a substance called hydrocarbonase in the human body to produce carcinogenic effects. This enzyme is prone to cancer in those with high vitality, while those with low vitality are not prone to cancer. 3.Will quitting smoking induce lung cancer The harm of smoking has a certain “hidden”, smoking causes lung cancer generally takes 20 to 30 years or longer. Similarly, the benefits of quitting smoking can only be seen slowly. Follow-up of smoking cessation shows that the incidence of lung cancer begins to decline after 5 years of cessation, and only after 15 years does the incidence rate become similar to that of nonsmokers. As the number of years of smoking cessation increases, the risk of lung cancer does not continue to increase but decreases, but the lung cancer-causing effects of the smoking experience do not completely disappear. Some people develop lung cancer after quitting smoking, not because they have quit smoking, but because they have been smoking for decades and have finally progressed from quantitative to qualitative changes. Of course, other causes of lung cancer include occupational carcinogens, air pollution, ionizing radiation, dietary factors, viral infections, fungal toxins, endocrine disorders, family genetics and so on. Therefore, although lung cancer and smoking are not necessarily equal, the two are inseparable as brothers. Remember, as long as you smoke, the more you smoke, the longer you smoke, the closer you are to lung cancer, and your life is in your hands, in the blink of an eye! In order to keep your health, it is wise to stay away from cigarettes and smoke.