The nevus is not a clinical term, but may refer to pigmented nevus, common wart, skin flab, lymphoma, etc. The reasons for their formation are different, as follows: 1, pigmented nevus: it may be related to congenital genetics or developmental defects, etc. Pigmented nevus comes from benign proliferation of melanocytes, pigmented cells formed during embryonic development, and when gathered in a certain area, it will form a mass of nevus cells. .