Pigmented nevus is a benign neoplasm composed of nevus cells, and almost everyone has them, either at birth or later in life, and they often increase with age, often significantly during development. Pigmented nevi are often symmetrical, with clear borders, smooth edges, and uniform color, and some may have short, thick black hairs throughout. Most of the moles are benign and their number is not directly related to health, but only a few of them can turn into melanoma. Repeatedly receiving chronic stimulation or improper treatment (such as picking or scratching with fingers, picking with needles or chemical corrosive agents) for a long time will promote the malignant transformation of pigmented moles. In addition, pigmented nevi located in friction-prone areas, such as the soles of the feet, palms of the hands and vulva, have a higher probability of malignant transformation than other areas. Signs of malignant change of pigmented moles: 1. The original moles increase significantly in size, deepen and brighten in color in a year. 2. The pigmentation of the original mole changes from brown to black, or from brown to black and brown with flowery spots. 3.The edges of moles become irregular or appear small satellite-like moles, or several moles fuse and the surface is uneven. 4.Puncture-like pain, itching and burning sensation appear locally. 5. The pigment of the mole disappears, and there is crust formation, inflammation, ulceration, watering or bleeding on the surface. If 1~2 of the above changes occur, you should go to hospital for specialist examination in time for early diagnosis and treatment. Treatment of pigmented nevi Most pigmented nevi do not need treatment. For nevi that are stimulated by friction for a long time, surgical excision treatment is preferred, and combined with histopathological examination, malignant melanoma can be excluded in time. Pigmented nevi such as facial nevi, which are small in size and have little possibility of malignant transformation and require treatment for cosmetic reasons, can be removed by CO2 laser cautery. For certain large pigmented nevi, such as congenital giant pigmented nevi, which are not suitable for CO2 laser cauterization, the Q-switched ruby laser can be used to remove the melanin. Laser treatment is relatively fast and simple, but the following two points should be noted: 1. to scar formation: the cautery process is likely to produce atrophic or hypertrophic scars. Scar generation is closely related to the size of pigmented nevus area, the depth of nevus cell involvement and the onset site. Pulsed CO2 laser has a shorter pulse width and less thermal damage to the surrounding normal tissues than normal CO2 laser, so the scarring is milder. Therefore, pulsed laser is the best choice for cosmetic treatment. In addition, it is very important to clean the wound after surgery and apply topical antibiotic ointment to prevent secondary infection. The general healing of the wound takes 10~14 days. 2.To the possibility of malignant change: There is no clear conclusion whether laser has the possibility of causing malignant change of pigmented nevus. However, when treating with CO2 laser, the nevus cells should be removed as much as possible, and the recurring nevus should be removed by CO2 laser or surgically in time according to the situation. There is not enough data to conclude whether laser treatment of giant congenital pigmented nevi will increase or decrease the possibility of their transformation into malignant melanoma.