Lung cancer is the most common primary malignant tumor of the lung and is currently the leading cause of cancer deaths worldwide. China’s urban malignant tumor mortality survey shows that lung cancer ranks first, with about 600,000 people dying from lung cancer each year. Smoking has been recognized as the most important cause of lung cancer. Currently, China has 1/3 of the world’s smokers, and about 1 million people die every day from smoking-related diseases such as lung cancer, while 80% of male lung cancers and 19.3% of female lung cancers are attributed to smoking. In clinical practice, we refer to the number of cigarettes smoked per day x the number of years smoked as the smoking index for lung cancer. If you smoke an average of 20 cigarettes per day and have been smoking for 20 years, your smoking index is 400. If you smoke 30 cigarettes per day and have been smoking for 15 years, your smoking index is 400. If you have smoked 30 cigarettes a day and have been smoking for 15 years, then your smoking index is 450. If your smoking index is greater than 400, you are 7 to 20 times more likely to develop lung cancer than non-smokers. Experts classify people with a smoking index of more than 400 as a “high-risk group” for developing lung cancer, meaning those who smoke most severely, figuratively speaking, the “three 20s” – those who have smoked for more than 20 years The three “20s” are those who have smoked for more than 20 years, those who started smoking before the age of 20, and those who smoke more than 20 cigarettes a day. If you meet any of these three criteria, you are likely to develop lung cancer. Below, we analyze each of the 3 characteristics that may cause lung cancer. 1. Smoking for more than 20 years Tobacco is the only consumer product that has been proven to cause death in users. Tobacco contains hundreds of complex chemical components, and there are more than 40 kinds of carcinogenic substances in the smoke produced by smoking, and more than 10 kinds of cancer-promoting substances, among which the most harmful substances are carbon monoxide, tobacco tar and nicotine, all of which have carcinogenic and cancer-promoting effects. A worldwide survey on the causes of lung cancer shows that the risk of lung cancer in smokers is 12-24 times higher than in nonsmokers, and the risk in lifelong smokers is 20-40 times higher than in nonsmokers. 1990, a study by the Centers for Disease Control and Prevention showed that 85% of lung cancer deaths are caused by smoking. The more cigarettes smoked, the longer the number of years smoked, and the drier the age at which smoking began, the higher the lung cancer mortality rate. The study also suggests that 96% of lung cancer patients have smoked for more than 20 years. In the case of a fixed amount of smoking, the incidence of lung cancer gradually increases with the increase in the number of years of smoking. 2. Starting the first cigarette before the age of 20 The age at which an individual starts smoking may be an independent risk factor for the development of lung cancer. It was found that the risk of lung cancer was higher for men who smoked before the age of 19 and for women at the age of 25. The younger the age of smoking initiation, the greater the likelihood of lung cancer development. Studies in the United States have shown that the relative risk of lung cancer for those who started smoking at an age younger than 15, 15 to 19, 20 to 24, and 25 years of age or older was 15.10, 12.81, 9.72, and 3.21. It is clear that as the age of smoking increases, the risk of lung cancer decreases. It is worth noting that there is a tendency of smoking at a younger age in China: the smoking rate of young people under 30 years old is on the rise, and the average age of people starting to smoke has decreased from 22.4 years old in 1984 to 19.7 years old, and these people will become a high-risk group for the occurrence of lung cancer. Therefore, we should vigorously strengthen the tobacco control work of young people. The risk of lung cancer increases with the increase of daily smoking and the number of years of smoking. The American Cancer Society survey confirmed that. The risk of lung cancer in smokers is several to tens of times that of nonsmokers, and the greater the amount of smoking, the higher the risk of lung cancer: 1 to 9 cigarettes per day is 3 to 15 times that of nonsmokers; more than 40 cigarettes per day is 19 to 30 times that of nonsmokers. In addition, researchers found that the incidence of lung cancer among smokers was 10.8 times higher than among nonsmokers in a large-scale observational study of more than 1 million people in three countries: the United States, the United Kingdom, and Canada. The annual mortality rate of lung cancer among nonsmokers was 12.8/100,000, 95.2/100,000 for those who smoked less than 10 cigarettes a day, and 235.4/100,000 for those who smoked more than 20 cigarettes a day, 18.4 times higher than that of nonsmokers. This shows that the greater the amount of smoking, the higher the mortality rate of lung cancer.