Nevi, also known as melanocytic nevi, commonly known as nevi, are the most common benign skin tumors in humans. Melanoma, also known as malignant melanoma, is a malignant tumor that originates from melanocytes and has a higher degree of malignancy.1. Nevus: It is divided into three types: junctional nevus, mixed nevus and intradermal nevus. Moles formed later in life are flat and black at first, and moles at this stage are called junctional moles. With age, moles slowly bulge up and become black or light brown, which is then called mixed nevus. Later, the nevus may bulge on the surface of the skin in a hemispherical shape, and there may be hair in the center, which is called an intradermal nevus. Most of the various types of nevi do not need treatment and have no effect on health except for aesthetics; 2. Melanoma: It is closely related to long-term sun exposure, and trauma, viral infection and low immune function of the body may also be related to its occurrence and development. The edge of melanoma is often swollen and expanded, with fast growth, deepened pigmentation, nodular elevation on the surface, easy to ulcerate and bleed, and satellite nodules or metastases appear rapidly after injury, which should be surgically removed immediately once diagnosed. Note that moles may develop into melanoma. If a mole suddenly increases in size or localized elevation, uneven color, irregular edges, surface rupture and bleeding, and pain or itching are felt within a short period of time, you should promptly seek medical attention, undergo professional examination, and be treated under the guidance of a doctor.