From the cytological classification, pigmented nevi can be divided into two categories: non-cellular nevi and cellular nevi. 1.Non-cellular nevus: Non-cellular nevus can be divided into two kinds, one is called freckle and the other is called pigmented nevus. It is a kind of yellowish-brown, small rash, which occurs on the face and other exposed parts of the body, often related to sunlight exposure. Some young girls’ freckles are very obvious in the spring and summer, but most of them fade away or are not obvious after the fall, which often brings them troubles. Age spots on the face or arms of the elderly also belong to this category. Freckles are only pigmentation in the epidermal basal layer of the skin, and no nevus cells are seen. Pigmented spots are black patches on the surface of the skin that are larger than freckles, in small patches or large areas. Some of them are detected at birth, while others are deepened and discovered as the child grows up. Pigmented spots are only pigmentation on the surface of the skin, and the problem of malignant change. 2.Cellular nevus: Classified from the tissue structure of skin cells, cellular nevus can be divided into five different types, namely, intradermal nevus, junctional nevus, mixed nevus, nevus of lan and juvenile nevus. Among these five types of nevi, the latter four have the tendency of malignant transformation and should be noted. However, the first three are usually found on the surface of human skin, namely, intradermal nevus, junctional nevus and mixed nevus. They have their own characteristics in terms of size, color, location, morphology and histological structure, etc. The following is a brief description and identification. Intradermal nevus: Size: limited granules of 1-2mm or large black spots; Color: no pigmentation change, or from light brown, gray-black to dark black; Location: can be seen in various parts of the body. The surface is flat or slightly above the skin surface, often with hair growth. Histological structure: nevus cells are in the dermis and contain melanin; malignant tendency: none. Interdigital nevus: 2-5mm in size, appearing independently in all parts of the body; color: light brown, brown-black, greenish gray, or blue-black; location: on the palm of the foot, palm of the hand, external genitalia, scrotum, etc.; morphology: smooth surface or slightly above the surface, no hair growth; histological structure: active nevus cells at the epidermal-dermal junction; malignant tendency: yes! If the color deepens, the lesion increases or satellite spots and surface rupture appear, it should be treated early. Mixed nevus: size: irregular, granular or flaky; color: from darker to dark black; location: seen in all parts of the body; morphology: not standard, difficult to distinguish from the above two, may have hair growth; histological structure: intra-dermal nevus and junctional nevus co-exist; malignant tendency: yes! There is the possibility of malignant transformation with the vitality of junctional nevus.