A pigmented nevus is a benign skin tumor composed of nevus cells, and the probability of malignant transformation of a pigmented nevus is not very high in clinical practice. When local malignancy occurs, the first symptom is not the local discomfort, but the morphological reaction. For example, patients may find that their pigmented nevi are significantly larger in scope, and the edges are significantly irregular and uneven in color, and some patients may have recurrent rupture and bleeding, which may be painful and itchy, but most patients do not have significant abnormal sensations; other patients may have small black dots in the surrounding areas like satellites. The distribution of the characteristics. Therefore, in clinical practice, if a patient’s pigmented nevus changes in form, he or she should consult a doctor in time, and should not wait until he or she feels uncomfortable before coming to the doctor.