Pigmented nevus, also known as nevus cell nevus, melanocytic nevus, and nevus nigra, is a benign disease characterized by the color change of skin and mucous membrane 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, we should be alert to the fact that a very small number of pigmented nevi become malignant. Classification 1. Intradermal nevus: the most common. It occurs on the skin of face and hairline, and its size varies, with large ones reaching several centimeters and even involving half of the side of the neck. It is raised on the skin, hairy, light brown or light black, with clear borders. It consists of small nevus cells. The nests of nevus cells are within the subepithelial connective tissue (i.e., located in the dermis). The epithelial layer on the surface of the nest of nevus cells is normal. Generally, no cancer occurs. 2.Junctional nevus: it can be evolved from intradermal nevus, or it can occur alone. It can occur at any age, but is more common in infants and children. The lesion is flat, brownish-black or blue-black, and the boundary can be clear or unclear. They are usually small in size, mostly within a few millimeters. The surface is smooth and hairless. They may remain unchanged for a long time, and a few of them may fade on their own, but they are more prone to malignant changes. Half of the nest of nevus cells is in the underlying epidermis, and the other half is in the superficial connective tissue under the epithelium, that is, in the superficial dermis. There is a possibility of cancer. 3.Compound nevus: It is common in children, and most of the lesions are slightly protruding from the skin surface, a few of them are papilloma-like changes, usually hairless, and the volume increases and the color becomes darker with age. The junctional nevus in compound nevus can be malignant. The pathology is characterized as a mixed form of intradermal nevus and junctional nevus in the process of nevus cells entering the dermis, often with both intradermal nevus and residual junctional nevus. Clinical manifestations Prevalent groups Pigmented nevus can occur at any age, mostly appearing later in life. Disease symptoms pigmented nevus is asymptomatic, if there are symptoms, be alert for malignant transformation. They appear as black, yellow-brown, or blue, flat or slightly elevated spots or patches; a few are also colorless pigmented nevi. A very small percentage of pigmented nevi will undergo malignant changes and become malignant melanoma. It has been reported that about 50% of malignant melanomas originate from pigmented nevi. If a pigmented nevus develops in a short period of time with accompanying symptoms and changes in color and texture, it must be alerted and surgically removed as soon as possible. The following clinical changes indicate that a pigmented nevus may become malignant: 1) pain and itching; 2) increase in size or the appearance of small “satellite nevi”; 3) color changes of different shades; 4) inflammatory redness around the nevus; 5) hard nodes or ulcers in the nevus. Treatment When facial nevus affects the beauty, it can be removed surgically. If smaller moles are removed, the skin edges can be subconsciously peeled off and then directly pulled together and sutured. If the area is larger, the nevus can be excised in stages, or it can be excised once and then free skin implants or adjacent flap transfer can be performed. If malignant nevus is suspected, surgical excision and biopsy should be performed; the incision should be made on the normal skin outside the boundary of the nevus.