Nevus is a congenital abnormal skin change that is limited in nature. Most of them exist at birth, while a few appear after birth and are mostly persistent. Those with melanocyte-based nevi are called pigmented nevi; those with vascular abnormalities are called vascular nevi (birthmarks); those with epidermal hyperplasia are called verrucous nevi, etc. Narrowly defined nevus refers to nevus cellular nevus composed of nevus cells, which is called pigmented nevus because it mostly has melanin. According to histological examination, pigmented nevus can be divided into junctional nevus, mixed nevus and intradermal nevus: histological examination of junctional nevus shows that nevus cells nest between epidermis and dermis, hence the name. Histological examination of mixed nevus shows that many nests of nevus cells exist not only at the junction of epidermis and dermis, but also in the dermis. Histological examination of intra-dermal nevus shows that nevus cell nests exist only in the dermis. A small number of pigmented nevi exist after birth and are called congenital pigmented nevi. The size of congenital pigmented nevus varies, and some of them can affect most of one limb or trunk, and the skin on the surface of nevus is uneven, proliferated and has many hairs, which is called giant congenital pigmented nevus. However, if the pigmented nevus enlarges, bulges, bleeds easily or ruptures within a short period of time, it may be a sign of malignant transformation of pigmented nevus and should be treated promptly. In particular, pigmented nevi occurring on the palmoplantar and finger (toe) ends should be treated in time. Other common nevi include: vascular nevus, i.e. capillary dilation nevus, which is a red pinhead-sized to bean-sized vascular dilation change. There are also red filiform changes. Verrucous nevus is a verrucous lesion that is raised on the surface of the skin in the form of papillary growth. The lesions are arranged in a linear or band-like pattern, and may also be distributed in a linear pattern along a limb. Sebaceous nevus is a nevus with sebaceous gland proliferation, commonly found on the scalp or face, and is a coin-sized or oblong plaque. In adolescence, the sebaceous glands increase in size and the surface becomes papilloma-like or warty. Connective tissue nevus, which is relatively rare, is caused by the proliferation of collagen or elastic fibers in the dermis, and appears as papules or nodules from the size of a pinhead to a bean, pale white to light brown, in groups or in bands, and is usually found on the trunk. Treatment of pigmented nevus is mainly surgical excision, skin grafting and dilator repair.