Malignant tumor is a new organism in which normal cells of human body grow without restriction under the action of various carcinogenic factors. There are many reasons causing tumor and its occurrence is the result of the joint action of various factors. Physical carcinogenic factors include electric radiation, long-term exposure to ultraviolet radiation, long-term inhalation of large amount of asbestos, aluminum oxide and glass wire, etc. can induce the occurrence of malignant tumors. 2.Chemical carcinogenic factors Nitrosamines are recognized as carcinogenic substances. Foods containing more nitrosamines include: pickled foods such as kimchi, cured meat, etc., and the content is higher in spoiled vegetables and foods, the main carcinogenic substance in coal tar is 3 and 4 benzopyrene, and the content is higher in automobile exhaust, coal smoke, cigarette smoke and smoked food, aflatoxin is widely present in moldy foods, and the content is higher in moldy peanuts, corn and cereals. Aflatoxin is widely found in moldy foods, and is higher in moldy peanuts, corn and cereals. Some viruses, parasites and bacteria are closely related to tumors, such as herpes virus, some schistosomes, Helicobacter pylori, etc. 4.Genetic factors When it comes to heredity, first of all, it is necessary to clarify a concept that it is not the direct heredity of tumor itself, but only the susceptibility to tumor, on the basis of which the participation of other external carcinogenic factors is needed for tumor to occur. 5.Immune function Many researches have proved that the immune status of the body has a close relationship with the occurrence of tumor, if the immune function is low, it is prone to malignant tumor. 6.Endocrine disorders The occurrence of certain malignant tumors is related to endocrine disorders, such as the occurrence of breast cancer may be related to excessive estrogen, etc.