There are 40-50 moles on every person. Generally, they are normal without any discomfort, but there are a few moles that may become malignant and should be alerted. A nevus originates from melanocytes and will rise above the skin surface if malignant changes occur. If a nevus has hair growth, it is called intradermal nevus, which is mostly benign and usually will not become malignant; if a nevus has no hair growth, is higher than the surface of the skin and is light black or dark brown in color, it is called junctional nevus, which has a certain chance of malignant transformation. Malignant melanocytoma is the most malignant tumor in the skin, which originates from melanocytes and can also be derived from junctional nevus. Some people counted 79 cases of skin malignant melanocytoma, 49 of which occurred on the basis of nevus. Therefore, when people find a nevus growing on their body, they should pay attention to observe the changes and do not use corrosive drugs or herbal medicine for external application, so as not to cause epidermal rupture to form ulcers that are difficult to heal and more likely to cause malignant changes. If malignancy is suspected, or if the following conditions occur, you should go to hospital for examination and early treatment. Appearance of moles: Moles with smooth surface, hairless growth, light or dark brown color are mostly junctional moles, which have a higher risk of malignant transformation. Location of nevus: If nevus is located on the bottom of foot, vulva, palm, waist or head and neck and other parts that are often subject to friction, it is prone to malignant change and should be removed by surgery early, which can basically cure it. Pay attention to the changes of nevus: when the nevus increases significantly in a short period of time, hair loss, itching, pigment deepening or bulging, and the epidermis is nodular, malignant change is more likely.