Lung cancer is the most common primary malignant tumor of the lungs. Symptoms of lung cancer are usually regarded as coughing, coughing up blood and so on. 1.Smoking This is currently recognized as the most important risk factor, the longer the smoking time, the larger the amount, the higher the risk. It is generally recognized that smoking index greater than 400 years is one of the high-risk factors of lung cancer. Passive Smoking Many carcinogenic substances in cigarette smoke can be inhaled into the deep part of lungs passively by the surrounding people. Some lung cancer patients may be inhaling “second-hand smoke”. It is estimated that 10% of lung cancer in big cities may be caused by air pollution. In addition, indoor small environment pollution, including oil smoke in cooking process and radioactive materials (radon, etc.) in building decoration materials, are carcinogenic substances. Occupational factors: Asbestos, arsenic, chromium, soot, tar, polycyclic aromatic hydrocarbons (PAHs) in oil and radiation in the working environment. Dietary and nutritional factors Insufficient vitamin A content in food or poor lifestyle.