Nevus refers to nevus in medicine, which is generally caused by benign proliferation of melanocytes in the skin, the etiology of which is mostly unclear, and may be related to congenital heredity, or acquired factors such as ultraviolet irradiation and trauma. Nevus is melanocyte proliferation in various reasons, melanocytes in various parts of the skin gathered into the material, may be related to congenital developmental causes, such as dermal melanocytosis is in the embryonic development, melanocytes from the neural crest to the epidermis when the movement of the epidermis stays in the dermis caused. Acquired ultraviolet radiation, skin trauma, and changes in the body’s hormone levels may also induce the development of moles. If a mole seriously affects aesthetics or develops abnormal symptoms such as itching or sudden enlargement, it is necessary to consult a dermatologist for active treatment under a doctor’s guidance.