There are black moles on every person, so what is the cause of the formation of black moles? It is formed by the abnormal increase and accumulation of melanin particles secreted by melanocytes or melanocytes in the skin. For example, the common nevus is formed by the accumulation of increased melanocytes into nests or clusters; while in nevus of Ota and freckle-like nevus, the increased melanocytes are scattered and can present different colors due to their different distribution shades. There are many kinds of nevi, the most common ones are limited nevi (divided into junctional nevi, intradermal nevi and mixed nevi according to their depth), in addition to giant nevi (congenital nevi with huge area), halo nevi (nevi with surrounding circles of skin pigmentation loss), simple freckle-like nevi (nevus), freckles (appearing on exposed areas such as face, brown in color, and deepening after sun exposure), coffee-milk spots (light brown patches appearing at birth), and coffee-milk spots (nevus). (light brown patches that appear at birth), chloasma (light brown patches on the cheeks and forehead of healthy women), nevus of Ota (greenish-brown nevus on the upper jaw of the eye), nevus of Ito (greenish-brown nevus on the trunk and limbs), blue nevus (blue macules or nodules), etc. Which moles may become malignant? The malignant change of moles is more closely related to the type of moles, trauma, chronic irritation, and inappropriate treatment. However, should we not remove all moles because they have the possibility of malignant change? That is not necessary. Then, what kind of moles should be treated? Any nevus that grows on the palms of hands, feet and plantars, red lips, external genitalia, or on the neck and male lips, which are often stimulated by repeated friction of collar or shaving beard, is prone to malignant transformation over time, and it is clinically proven that nevi on mucous membrane, genitalia, palms and plantars are mostly junctional nevi with higher malignant transformation rate. Therefore, it is quite necessary to treat nevi in these areas, and regardless of whether the nature or abnormality has been clinically determined, preventive excision should be made early and pathological examination should be routinely performed to avoid future problems. For nevus in other areas, if you find that the scope of nevus is enlarged, color is deepened, flat becomes convex, surface becomes rough, blood vessels are dilated, inflammation, bleeding, secondary infection, satellite nevus of different sizes grow around the nevus, painful and itchy symptoms and other abnormalities, you should pay great attention to them and seek timely medical treatment, and send the specimens for pathological examination to observe whether they are malignant.