Tobacco is native to the Americas, Indians found that it contains substances that can excite the nerves, in tribal meetings and rituals to smoke its burning smoke, the Spanish colonists brought it to Europe, the earliest Spanish sailors back home when puffing clouds, once made the people back home alarmed, think they deal with the devil, but soon the use of tobacco was popularized throughout Europe and to the world. 18th century when tobacco was introduced to China. A, tobacco in harmful substances Cigarettes ignited smoke contains dozens of harmful substances, including carbon monoxide, nicotine, 3, 4-benzopyrene, nicotine tar and other alkaloids. Nicotine, an alkaloid, is neurotoxic, especially for insects is fatal, but can stimulate human nerve excitement, long-term use tolerance will increase, but also produce dependence. According to research three cigarettes or half cigar smoke contains all the nicotine can kill people, some people have done experiments: 1 drop of pure nicotine on the tongue of a dog, the dog died after a few minutes; 1 drop of nicotine can also kill a horse weighing 200 kg. But the nicotine inhaled by people who smoke is only a very small part of it. Even a small amount of nicotine also has a variety of biological effects, is inhaled into the body, the respiratory tract, cardiovascular, gastrointestinal, nervous system and liver, kidney and other organs have different degrees of damage. There is a causal relationship between smoking and lung cancer The causes of lung cancer are: (1) smoking, (2) air pollution. Smoking is a small but highly concentrated air pollution. The incidence of lung cancer will be higher if you live and work in an environment with air pollution and smoke at the same time. If two carcinogenic factors exist at the same time, they have the effect of strongly promoting each other to cause cancer. ⒈ Tobacco contains carcinogens. The carcinogenic effects of carcinogens in tobacco such as 3.4-benzopyrene and tobacco tar are unanimously recognized. ⒉ Epidemiological investigation. Researchers conducted 1 large-scale comparative observation of more than 1 million people in 3 countries, the United States, the United Kingdom, and Canada. The results showed that the incidence of lung cancer, smokers dry for non-smokers 10.8 times; annual mortality rate of lung cancer, non-smokers 12.8/100,000; smoking less than 10 cigarettes per day for 95.2/100,000; smoking more than 20 cigarettes per day for 235.4/100,000, 18.4 times higher than non-smokers. China’s Shanghai Cancer Institute announced as early as 1986, the incidence of lung cancer in Shanghai has reached the same level as the United States, lung cancer patients, non-smokers accounted for only 1/3. can be seen, the main risk factors for lung cancer is not air pollution, but smoking. Western studies have shown that various air pollution has some effect on lung cancer, but its effect is lower than that of smoking. The following factors are associated with the susceptibility of smokers to lung cancer: ⒈ smoking for more than 20 years; ⒉ smoking since the age of 20; ⑶ smoking more than 20 cigarettes a day; singing one after another, with a short smoking period; being careful about the amount of smoke inhaled per puff, most of which is inhaled into the lungs; choosing to smoke while having chronic bronchitis. Modern research has confirmed the carcinogenic effects of tobacco, which has drawn increasing attention, and many places have started to ban smoking in public places to protect public health. Many countries have laws that require the words “Smoking is harmful to health” to be printed on cigarette packs. In the People’s Republic of China, the law prohibits cigarette advertising in any media or public places. Thailand requires large pictures of the dangers of smoking, such as a smoker’s damaged teeth and a smoker’s blackened lungs, to be printed on cigarette packs to alert smokers to the effects of smoking cessation. Bhutan also became the first smoke-free country by banning all tobacco imports. Experts call on the whole society should vigorously promote the harmful effects of smoking, and at the same time can introduce some scientific methods to quit smoking, which will help to improve the success rate of quitting smoking and effectively prevent lung cancer or reduce the incidence of lung cancer.