Classification of pigmented nevus Pigmented nevus can be divided into junctional nevus, intradermal nevus and mixed nevus according to the location of nevus cells in the skin. 1. Junctional nevus has nevus cells and nevus cell nests mainly between the bottom layer of epidermis and dermis, characterized by flat or slightly higher than the skin surface, unclear border, smooth surface, hairless, varying luster, yellowish, greenish or dark color, and can be seen on any part of the body, mostly in young people and children. 2.Intradermal nevus, i.e. nevus cells and nest of nevus cells are gathered in the dermis, often flattened or higher than the skin in the form of warts, with dark brown or lacquer color, and evenly hairy. It is a common pigmented nevus in adults, with clear boundary and not easy to occur malignant transformation. 3.Mixed nevus in which nevus cells and nevus cells nest in the deep epidermis and also in the dermis is called mixed nevus. Commonly, the center of nevus protrudes from the skin surface, with long hair, and the surrounding area is diffusely distributed, with different luster and unclear boundary, which is the junctional nevus component. Mixed nevus and junctional nevus both have the possibility of malignant transformation. The parts of pigmented nevi that are prone to cancer 1. nevi in friction areas Some information shows that the cancer of some pigmented nevi is related to friction and external damage. Moles in friction-prone areas have a higher chance of turning into malignant moles. For example, pigmented moles growing on the palms and feet, neck, armpits, chest, head, back, genitalia and other areas susceptible to wear and tear have a high chance of malignant transformation and must be regularly observed or directly removed to prevent malignant transformation and metastasis. 2. Exposed moles Sunlight or ultraviolet rays may increase the chances of moles changing, so moles on long-term exposed parts are best to be removed. 3.Moles growing on the extremities Moles on the soles of the feet are a good site for melanoma. According to medical statistics, moles on the ends of the extremities, like those under the fingers or nails, should be paid special attention. 4.Moles of mucous membrane Moles of oral mucous membrane, conjunctiva, vagina and foreskin.