According to the origin of tumor cells, skin cancer is divided into many types, among which the more common ones are epidermis, soft tissue, melanocytes and hematopoietic cells, etc. In addition to these, a large proportion of skin cancer is metastasized to the skin from other tissues. Causes of skin cancer 1. prolonged exposure to ultraviolet radiation, i.e. prolonged exposure to sunlight; 2. exposure to ionizing radiation and radiation, which cannot be avoided in many cases; 3. exposure to excessive chemical carcinogenic substances in life, including asphalt, benzo(a)pyrene, etc., which stimulate the skin; 4. autoimmunity suppressed by foreign and self, or exposure to viral carcinogenic substances; 5. chronic inflammation and other stimuli Long-term effects on skin, like lupus erythematosus, long-term chronic ulcers, etc. Early warning symptoms of skin cancer 1.Skin ulcers with long duration and persistent good and bad or with small amount of bleeding and oozing 2.When nodules or ulcers appear on skin or sinus tracts previously irradiated by radiation. 3.Patients with solar keratosis develop effusion, rupture, and protrusion. 4.Beware of carcinoma in situ when the scar of the skin becomes red and erosion appears.