It is medically proven that smoking causes lung cancer. Why is smoking easy to cause lung cancer? Studies have proven that tobacco contains hundreds of complex chemical components, most of which are harmful to humans. These carcinogens can lead to DNA damage in bronchial epithelial cells, activation of certain oncogenes, mutation and inactivation of oncogenes, and transformation of cellular genetic information into cancer through different mechanisms. Eighty percent of lung cancers in men are attributed to smoking. Cigarettes contain the highest amount of nicotine and are the most toxic. Experiments show that the nicotine in 1 cigarette can poison a mouse, 40-60 mg of pure nicotine can poison a person. Currently, China has about 300 million smokers, and each year more than 1 million people die from lung cancer, coronary heart disease and other smoking-related diseases, a figure that exceeds the sum of tuberculosis, AIDS, perinatal diseases, car accidents and suicide deaths. Smoking is not only hazardous to the smoker’s health, but also to the health of non-smokers who passively inhale large amounts of tobacco smoke. The alarming thing is that the harm of “secondhand smoke” is almost as bad as smoking, and some people who live with smokers are six times more likely to develop lung cancer than the average person. The results of the study showed that the non-smoking wives of heavy smokers have a higher risk of lung cancer, and there is a dose-effect relationship. Husbands who smoke have a 30% increased risk of lung cancer in their wives. Children inhaling “second-hand smoke” not only affects development, but also predisposes them to diseases such as bronchitis and pneumonia. If the wife is pregnant and often inhales the smoke from her husband, it can harm the fetus and lead to miscarriage and fetal malformation.