Most nevi are benign, but only about 5% may develop cancer. Pigmented nevus is a benign disease characterized by a change in the color of the skin and mucous membranes due to the proliferation of nevus cells and the production of pigment. Pigmented nevi maintain a stable state for a long time and do not recur after surgical removal; however, a very small number of pigmented nevi should be alerted to malignant changes. Generally the volume of pigmented nevus suddenly becomes larger in a short time; the color of pigmented nevus becomes black and rough and uneven to touch; the surface is smooth, but symptoms such as erosion, ulceration, bleeding and swelling appear; it starts to itch and pain; satellite lesions, i.e. skin lesions, appear around the nevus with inflammatory redness, there is a possibility of malignant melanoma. Overall, the incidence of melanoma is 1 in 100,000, accounting for only 1 to 3 percent of all malignant tumors. For example, the first type of intradermal nevus is the most common. They occur on the facial skin and hairline. The skin is elevated, hairy, light brown or light black, and well-defined. It consists of small nevus cells. The nest of nevus cells is within the subepithelial connective tissue. The epithelial layer on the surface of the nest is normal. Generally, no cancer occurs. The second type of junctional nevus can occur at any age with a smooth and hairless surface. They can remain intact for a long time, but are more common in infants and children. The lesions are flat, brownish-black or bluish-black. They are generally small in size and a few can fade on their own, but are more prone to malignant transformation. They are composed of large nevus cells, with half of the nest in the underlying epidermis and the other half in the superficial connective tissue under the epithelium, i.e., the superficial dermis. There is a possibility of cancer. The third type of compound nevus is common in children, and most of the lesions are slightly protruding from the surface of the skin, and a few of them are papilloma-like, usually hairless, and may increase in size and darken with age. Some of the junctional nevi in compound nevi can become malignant. It is recommended to remove the nevus surgically, i.e., make a skin incision as round as possible at the circumference of the nevus, cut the skin and remove the nevus together with the skin and some subcutaneous tissues, as the trauma has the tendency to shrink to the center by itself after surgery, the trauma will become smaller and smaller, and eventually it can heal completely by itself. After laser mole removal, the mole tissue will be destroyed, and on the surface, although the mole is removed, if there is cancer, the cancer cells cannot be removed; and since the tissue is destroyed, biopsy cannot be performed to determine whether the mole is benign or malignant, and it will be troublesome if there is mole cell lesion.