Tobacco is generally a class 1 carcinogen.

The most harmful thing in tobacco is nicotine, in addition, nicotine and formaldehyde are regarded as the first grade carcinogens by the state, and there are many other items in tobacco that cause harm to the human body, so tobacco as a first grade carcinogen.

Long-term heavy smoking will lead to lung stimulation, prone to lung cancer disease, some people may also appear tongue cancer or stomach cancer, because smoking produces carbon monoxide or coal tar, etc., which may lead to DNA damage, so the human body in the activation of the oncogenes, able to inhibit the gene inactivation, leading to cellular mutation.

Quitting smoking reduces the risk of cancer:

After quitting smoking, the risk of lung cancer decreases slowly, and the time it takes to reach the same level as that of non-smokers depends on the length of the smoker's addiction to cigarettes and the amount of cigarettes smoked per day; it takes more than 10 years for those who have smoked a lot of cigarettes for a long time. Cigarettes were easier to quit because people were more educated. The authors also observed that lung cancer has become an increasing disease among people with lower economic incomes.

The risk of myocardial infarction decreased faster after quitting smoking than lung cancer, suggesting that it is nicotine and possibly carbon monoxide that can cause cardiovascular disease. Myocardial infarctions will decrease as a result of reduced nicotine levels within cigarettes and as more people are willing to quit smoking. Death statistics in the United States have begun to illustrate this point. Non-tumor respiratory diseases, such as chronic obstructive pulmonary disease, emphysema, etc., are irreversible, smoking cessation can only inhibit the continued deterioration of the disease. Nevertheless these patients should quit smoking as early as possible in order to gain full vigor.