Tobacco leaves contain toxic nicotine, also called nicotine. 1 g nicotine can poison 300 rabbits or 500 mice. If people are injected with 50 milligrams of nicotine, they will die.

Smoking is the most harmful to the respiratory tract, and it is easy to cause cough diseases such as laryngitis, tracheitis and emphysema. When smoking, smoke enters from the mouth, passes through the throat, trachea and bronchus, and enters the blood.

Smoking can make men lose Y chromosome and increase the risk of cancer.