Recently, a news about skin cancer in Nicholas Tse went viral online. Nicholas Tse has a mole on his scalp, which was once considered as skin cancer. Fortunately, the test results are benign, not cancer. However, this news has made some people in the society feel uneasy. "I also have a mole on my face. Is it a malignant tumor? " "My mole feels bigger recently. It can't be true, can it? " Which moles have cancer risk and which can be ignored? "In fact, you don't have to worry too much. Pigmented moles are mostly benign. " Professor Sun Jiaming from the Department of Plastic Surgery of Union Medical College Hospital said that moles are medically called pigmented moles, most of which are benign, and only about 5% may suddenly become cancerous. Pigmented nevus is a benign disease, characterized by the proliferation of nevus cells and the production of pigment, which leads to the color change of skin and mucosa. Pigmented nevus remained stable for a long time and did not recur after surgical resection. However, we should be alert to the malignant transformation of a few pigmented nevus. He emphasized that the volume of pigmented nevus suddenly became larger in a short time; Pigmented nevus turns black and feels rough and uneven; The surface is smooth, but there are symptoms such as erosion, ulcer, bleeding and swelling; It will itch and hurt at first; There are satellite lesions around the nevus, that is, skin lesions, and inflammatory redness around them, which may lead to malignant melanoma. Overall, the incidence of melanoma is one in 100,000, accounting for only 1%-3% of all malignant tumors. Such as the first kind of intradermal nevus is the most common. Common in facial skin and hair. The skin is prominent, hairy, light brown or light black, with clear boundaries. It is composed of small nevus cells. Nevus cells are embedded in the connective tissue under the epithelium. The epithelial layer on the surface of the nevus cell nest is normal. Cancer does not usually occur. The second kind of borderline nevus can occur at any age, and the face is smooth and hairless. It can remain intact for a long time, but it is more common in infants. The lesions were flat, brown-black or blue-black. Generally, the volume is small, and a few of them can fade by themselves, which is more likely to become malignant. It consists of large nevus cells, half of which are at the bottom of epidermis, and the other half are in the superficial connective tissue under epithelium, that is, the superficial dermis. There is a possibility of cancer. The third compound nevus is common in children. Most skin lesions protrude slightly from the skin surface, and a few show papilloma-like changes, which are generally hairless and can increase and darken with age. The borderline nevus in compound nevus can be malignant. Dr. Liu Jiafeng, Plastic Surgery Department of Union Hospital, suggested surgical removal of nevus, that is, making a skin incision as round as possible around the small nevus. After the skin is cut, the nevus is removed together with the skin and some subcutaneous tissues. Because the wound tends to contract towards the center after operation, the wound will become smaller and smaller, and eventually it will completely heal itself. When laser removal is completed, the nevus tissue will be destroyed. On the surface, although the mole is removed, if there is cancer, cancer cells cannot be removed. Because the tissue is destroyed, it is impossible to determine whether the nevus is benign or malignant by biopsy, and it is very troublesome if there are nevus cell lesions.