Nevus is a pigmented plaque on the skin. It is composed of nevus cells with appearance in the deep dermis, which contains melanosomes. Nevus is very common, almost everyone has more than one. According to the location of nevus cell aggregation, the nevus can be divided into junction nevus (in epidermis), intradermal nevus (in dermis) and composite nevus (in epidermis and dermis). Generally, junctional nevus is more active and prone to malignant transformation.
Normal pigmented nevus is a process of occurrence, development and regression. Most of them occur in childhood, reach the peak in young and middle-aged people, and tend to fade away in old age. Most nevi are benign and harmless. However, a small number of nevus will become malignant. It is generally believed that nevus is prone to malignant transformation under the following conditions:
(1) Nevus occurred in exposed parts, easily abraded parts, perineum and lower limbs;
(2) The morphology of nevus was irregular and asymmetric;
(3) The distribution of nevus pigment was disorderly;
(4) Nevus larger than 5 mm, and gradually increased;
(5) Nevus itches and ulcers. If the above conditions are found, surgical resection should be taken, and pathological examination should be done, and laser, freezing and other destructive treatment should not be used.