1.External carcinogenic factors Chemical carcinogenic factors: long-term exposure to aromatic amines, nitrosamines, arsenic, chromium, cadmium, nickel, etc. will increase the risk of cancer. Physical carcinogenesis: Long-term exposure to ionizing radiation, sunlight and ultraviolet radiation will increase the risk of cancer. Biological carcinogenesis: having viruses, parasitic diseases and chronic inflammatory stimuli will increase the risk of cancer. 2.Intrinsic carcinogenic factors Genetic factors, racial factors, gender and age, hormonal factors and immune factors are related to cancer. Dietary factors are closely related to the occurrence of tumor, such as the long-term use of pickled, smoked and moldy food will increase the risk of cancer. 4.Smoking The scientific community believes that 30% of cancers are related to smoking among various factors that cause cancer. 5.Depression and stress Long-term bad mood or stress will lead to the decrease of body resistance, thus increasing the risk of cancer. 6.Obesity Excessive obesity can also cause cancer.