Most people have moles, but the probability of cancer is very small. Melanocytes are normally evenly distributed under our skin, but if they divide and proliferate excessively to form a mass, it is called a melanoma, which is often referred to as a “mole”, and when this division and proliferation gets out of control, it evolves into a melanoma. Malignant melanoma is a very serious skin malignancy. Risk factors for malignant melanoma include skin color, race, sun exposure, and local trauma. Some malignant melanomas originate from pigmented nevi. Since limb-type malignant melanoma is more common in Chinese, special attention should be paid to pigmented nevi occurring on the hands and feet, especially when the original pigmented nevus has significant changes and is larger than 3 mm in diameter. The older you are, the greater the possibility of malignant melanoma, so middle-aged and elderly people should pay more attention to pigmented nevi that have changes or are located in high-risk areas. For congenital pigmented nevi, if they are large in size, they should also be given enough attention, especially if they change after middle age. If our “nevus” has the following ABCDE manifestations, we should pay high attention to it and go to a regular hospital for pathology to exclude melanoma. In addition, there is a consensus that congenital pigmented nevus with a diameter greater than 20 cm has a high rate of malignancy; acquired pigmented nevus with a diameter greater than 5 mm (black spot under the nail wider than 3 mm) should be alerted, and the older the patient is when it occurs, the greater the possibility of malignancy; Chinese patients with larger black spots on the distal end of the fingers, toe and metatarsal joints, heels, etc. should be investigated for limb-type melanoma; if a pigmented nevus occurs in size, color, symptoms and status (nodules occur), the patient should be alerted. If a nevus changes in size, color, symptoms and status (nodules or ulcers), it suggests the possibility of malignant change. To prevent moles from becoming melanoma, the simplest thing is to pay attention to moles in the following locations: among them, we must focus on moles near the palms of hands, feet and genitals, which can become lesions due to frequent friction; secondly, moles on the head and neck, which can become lesions due to long-term sun exposure .