Nevus refers to pigmented nevus, the cause of pigmented nevus on the face is unknown, which may be related to congenital factors, external stimuli, age factors, racial factors and so on. 1. congenital factors: may be in the process of development of genetic mutation, melanocytes from the neural crest to the epidermis in the process of migration abnormalities, resulting in the localization of black cell aggregation. 2. External stimulation: for example, long-term ultraviolet radiation, local trauma, friction, light and other stimuli, is a triggering factor. 3. Age factor: pigmented nevi appear in early childhood, the number will gradually increase, and reach the peak in adolescence and gradually decrease in number after middle age. 4. Racial factor: Individual race and skin color may affect the number of pigmented nevi. There may be other reasons for the high number of moles on the face, so you need to go to the regular hospital in time for examination to clarify the cause of the disease.