A black mole on the skin is usually a pigmented nevus, also known as a nevus cell nevus, which is a benign skin tumor originating from melanocytes. A black mole is generally a nevus cell nevus, also known as a melanocytic nevus, a benign skin tumor originating from melanocytes. It is a developmental abnormality in which localized aggregation of melanocytes can occur during the movement of melanocytes from the neural crest to the epidermis, which begins to appear several years after birth, and increases the number of colored nevi in exposed areas when exposed to ultraviolet light. Histologically, according to the location of nevus cells within the skin, they can be divided into intradermal nevus, junctional nevus and compound nevus. When a nevus is present, the skin is a flat or raised patch or macule, or it may be wart-like or nodular, etc. The surface is hairless or hairy, and it may appear black because of the high pigment content within it. Nevus cell nevus generally does not require treatment, but if there is a sudden increase in localized size, bleeding, etc., it is necessary to consult a doctor in time to clarify the nature of the lesion and target treatment.