Smoking is a cancer risk. The main reason why smoking increases the chances of causing cancer is that tobacco releases a variety of cancer-causing chemicals during the combustion process. These include benzene, styrene, formaldehyde, N-nitrosodimethylamine, polycyclic aromatic hydrocarbons (PAH), N-nitrosamines, aromatic amines and heavy metals. Among them, formaldehyde, N-nitrosamines as the representative of the main carcinogen components will induce the imbalance of human proto-oncogenes and anticancer genes, resulting in the loss of normal cell apoptosis, showing the characteristics of malignant proliferation. Lung cancer, prostate cancer and other diseases are induced. Therefore, the carcinogenicity of smoking is confirmed by scientific research. In addition to the direct residue of harmful substances in the mucous membranes of the respiratory tract and the alveoli, there is also the possibility that the harmful substances may be suspended and adhered within family members, thus increasing the chances of family members coming into contact with each other, and thus increasing the risk of cancer. Therefore, it is important to quit smoking as soon as possible, especially if there are pregnant women and children in the family, it is even more important to go smoke-free. This is to avoid incalculable damage to the development of the fetus and the health of the newborn.