If a pigmented nevus occurs in friction areas, such as palms, soles of feet, waist, armpits, perineum, neck and other friction-prone areas, it is prone to malignant transformation, so consider surgical excision plus biopsy as much as possible, once a pigmented nevus becomes malignant, it becomes melanoma. Melanoma is a kind of tumor with very high malignant degree, easily metastasized and very difficult to be completely cured. However, if a pigmented nevus has one of the following conditions, it indicates that malignancy may occur: 1) sudden increase in the area of the pigmented nevus; 2) unclear boundary; 3) uneven color or sudden darkening within a short period of time; 4) surface erosion, ulceration, bleeding or swelling; 5) conscious local pain, itching or signs of infection under the pigmented nevus or combined with epidermal cysts; 6) small satellite foci around the pigmented nevus, i.e., many small skin lesions grow around the pigmented nevus. many small skin lesions grow around the pigmented nevus. If one of the above six items appears, we should be highly alert to the possibility of malignant transformation of pigmented nevus.