Most pigmented nevi are benign tumors and most of them are lifelong and do not become malignant and therefore do not need to be treated. Only a very small number of moles turn into the dreaded malignant melanoma. Malignant melanoma is one of the most malignant skin malignancies, which can be secondary to a pigmented nevus or can start from normal looking skin, and is generally darker in color and can be flaky or nodular. In fact, there are three purposes of treatment for nevi: first, for cosmetic purposes, second, to prevent malignancy, and third, to relieve the inconvenience of life caused by pigmented nevi. Then those moles need to be treated, which are summarized as follows: 1. unsightly: mainly occurring in exposed parts, such as face and neck, with darker color, affecting the beauty. 2. Often stimulated by friction, with the possibility of malignant transformation: pigmented nevi occurring on the neck, scapula, waistline, chest and back, palms, toes, heels, perianal area, genitalia, etc. 3. Generally speaking, pigmented nevi occur before the age of 20-30, and most of them will gradually shrink or disappear after the age of 30, except for the face. If new pigmented nevi occur suddenly in middle-aged and old people, they are dangerous and need to be alerted. 4. If one or more longitudinal black-brown articles appear below the deck of the finger or toe, it is called nail nevus. If this kind of “nevus” is subject to some bad stimulation, such as water immersion, trauma, friction and infection, it will easily become malignant and must be treated early. 5.The darkening of pigmented nevus is not exactly a sign of malignant change: for example, in summer and autumn, when there is sufficient holiday light and the influence of ultraviolet rays, the skin color of human body is obviously deeper than that in winter and spring, the pigmented nevus will also become darker and larger accordingly; during pregnancy, puberty, or taking corticosteroids or oral contraceptives, all pigmented nevi can become darker and have a tendency to increase in size. 6.Most pigmented moles slowly increase with the growth and development of the body, which is a normal phenomenon. If individual pigmented moles suddenly expand rapidly, deepen and brighten in color, become red around, or even break down on the surface, bleed, crust, with pain or severe itching, satellite lesions appear around, and the nearby lymph nodes swell up, it should be considered that the pigmented moles are malignant, and medical treatment must be sought immediately. 7. For patients who have a history of malignant melanoma in themselves or in their family, the more the number of nevi in the whole body, the higher the chance of nevus malignancy. Once individual nevus is found to be darker, even if it occurs in hidden parts such as scalp or external genitalia, we should be more careful and remove it by surgery as early as possible if necessary.