Pigmented nevus refers to the most common benign tumors containing nevus cells, which are found in everyone, and which type of nevus is prone to malignant transformation has always been the most concerned question. To answer this question, first of all, to clarify the pigmented nevus typing, because different types of moles have different probability of malignant transformation, this article only introduces the common pigmented nevus, but also the most concerned about several kinds of nevus. First, common types of pigmented nevus 1, nevus cell nevus: the most common, including junctional nevus, mixed nevus and intradermal nevus. It is most common in the face and neck, but also in other parts of the body. Mostly occur in childhood, the number reaches the most in 20-29 years old, and each person has 20-30 moles on average; then the number of moles will decrease with age, and after 60 years old, each person has only 4-6 moles on average. Junctional nevus: a brownish-black spot with a smooth, hairless surface; pathologically the nevus cells are located at the junction of epidermis and dermis, so it is called a junctional nevus. Mixed nevus: the nevus is slightly elevated, with smooth surface and clear boundary; it is formed by a part of nevus cells of the junctional nevus entering into the dermis downward; pathologically, there are nevus cells in the epidermal-dermal junction and superficial layer of the dermis, so it is called mixed nevus. Intradermal nevus: manifested as more protruding hemispherical shape, the color changes to brown, sometimes even to skin color, may have hair. It is called intradermal nevus because the nevus cells enter into the dermis completely when the nevus is mixed in adulthood. Indications of malignant transformation: If nevus cells suddenly increase in size, ulcerate, bleed or satellite-like small nevus appears beside the nevus, it is necessary to consider the possibility of malignant transformation, and should go to the specialist for examination and treatment in time. 2, dysplastic nevus: although it is easy to be malignant, especially in the family with melanoma, but it is rare in the yellow race. However, this kind of nevus is common in white people, so foreign countries advocate that this kind of nevus should be excised as early as possible. It mostly occurs in adolescence or even after adulthood, mostly grows in chest, back and waist, slightly larger than common nevus, usually more in number, smooth or slightly elevated in the center, and the color can be brown, brownish-black or orange-red, with uneven depths and shades. 3.Congenital giant nevus: present at birth, more frequent in the head and face, back and waist. It is a large black patch with rough surface, often with black coarse hairs, such as animal skin, also known as “animal skin nevus”. As children get older, the surface can appear wrinkles or wart-like protrusions, about 10% of this mole can be malignant, so it should be excised and implanted as early as possible, those who can’t be excised should be closely observed, and those who have nodules and ulcers should be biopsied in time for pathologic examination. 4.Congenital nevus: it is present at birth, but its size is within 20cm (the size of adult). It is an irregularly shaped brownish-black spot, slightly elevated with age, with smooth or rough surface, sometimes with black hair. Congenital nevus has 0.1% malignancy rate. Therefore, it is better to remove small congenital moles. What kind of moles need to be treated? From the above mentioned problem of nevus malignancy, first of all, it should be clear whether it is congenital or acquired, congenital giant nevus is the most likely to be malignant, followed by congenital small nevus, and then it is the nevus on the soles of the feet, toes, palms of the hands, fingers, and under the nails because it is easy to be stimulated by friction and relatively easy to be malignant, and all of these should be excised as early as possible or observed closely, and excised in time if there is any change. No matter whether there is hair on the surface of the hemispherical protruding nevus on the head and face, basically it will not be malignant, except for the cosmetic needs, it can not be necessary to treat it. Signs of malignant transformation of pigmented nevus (ABCDE): A. Asymmetry, different shapes on both sides of a nevus; B. Irregular edges; C. Uneven color, the same nevus has different shades of color; D. Diameter more than 6mm; E. Bulging, i.e. a part of a nevus is elevated. When encountering these cases above, it should be excised for pathological examination as early as possible.