Lung cancer is not contagious. Generally, diseases that can be transmitted from the lung are commonly found in tuberculosis and many kinds of pneumonia, and the cause is mainly pathogenic microbial infection. Lung cancer is an abnormal proliferation of human tissues after mutation and has nothing to do with pathogenic microorganisms, so it is not an infectious disease and will not be contracted by infection. Smoking and passive secondhand smoke are high-risk factors for lung cancer, and the risk is many times higher than that of non-smokers, so patients are advised to quit smoking to reduce the incidence of lung diseases. In addition, occupational causative factors, such as working in asbestos factories, chemical plants or exposure to radioactive substances such as uranium and radium, can lead to a significantly increased risk of lung cancer. The occurrence of lung cancer is also related to genetic factors. Generally, patients with a family history of lung cancer have a higher chance of having tumors in the next generation. Some diseases have also been found to be closely related to lung cancer in clinical practice and are also high-risk factors for developing lung cancer, such as tuberculosis, chronic obstructive pulmonary disease, and idiopathic interstitial lung fibrosis. In addition, the intake of aflatoxin is also related to the occurrence of lung cancer, which should be prevented by active treatment of the primary disease, daily exercise, regular work and rest, and not eating food that has been stored for too long.