Pigmented nevus is what we call a nevus in daily life, which is a benign tumor of the melanin system and is composed of nevus cells. Simply put, the skin is divided into epidermis and dermis from the surface to the deeper layers. When nevus cells are located at the junction of lower epidermis and dermis, it is called junctional nevus; when nevus cells are located in dermis, it is called intradermal nevus; when some nevus cells are located in epidermis and some in upper dermis, it is called mixed nevus. When a pigmented nevus turns into cancer, there are several early signs as follows: a. Pigmented nevus usually appears from birth to 30 years old, and the appearance of new pigmented nevus after 30 years old should be suspected. If the pigmented nevus is repeatedly infected. If the pigmented nevus has a tendency to bleed. Sudden appearance of persistent itching in pigmented nevi. V. Inflammatory redness around the pigmented nevus or the appearance of satellite nevus around the nevus. Sudden loss of the original hair on the pigmented nevus. The surface of the pigmented nevus is moist or there is crust formation. If the pigmented nevus is repeatedly stimulated by friction or trauma for a long time, and there is a potential cancer factor. When hard nodes or ulcers or bleeding appear in the center of the pigmented nevus. X. Darkening of pigmented nevus is not an absolute indication of malignant change, because all pigmented nevi can become dark when they are sexually mature and pregnant. However, if any single mole becomes darker than other moles in a short period of time or becomes black unevenly, or if it increases rapidly, it is an early sign of cancer. Interpretation of pigmented moles: Everyone has pigmented moles. According to statistics, after careful body examination, there can be as many as 50 nevi in normal individuals, and generally there are 15 to 20 nevi on average. Because they are common, they are often disposed of carelessly and casually, and there are many lessons to be learned. Some people listen to the nonsense of fortune-tellers, and in order to “drive away the evil and make fortune”, they randomly spot moles in the street; some people do not know the depth and take corrosive substances at will; some people randomly scratch and dig, and the consequences are as light as scarring and deformity, or as serious as death! Therefore, it is really feasible to popularize medical knowledge, make patients understand medical reasoning and accept regular treatment by doctors. Most pigmented moles are benign and do not have any effect on health. Many people worry about the malignant change of pigmented moles, and it is not an empty wind. Firstly, some pigmented nevi are easily confused with some skin malignant tumors and often misdiagnosed each other; secondly, individual pigmented nevi are indeed related to melanoma to a certain extent, so we should pay necessary attention to black pigmented nevi and ask dermatologists to identify them when necessary.