Moles are pigmented nevi, which are benign skin tumors of melanocyte origin. There are many reasons for acquired moles, such as external environmental stimuli, age factors, racial factors, gender factors and so on. 1. External environmental stimulation: for example, long-term exposure to ultraviolet radiation, skin trauma, friction, surgery, laser and other stimuli may aggravate the chance of growing moles. 2. Age factor: Nevus pigmentosus appears behind the ear in childhood, the number increases gradually, and peaks in adolescence. 3. Racial factor: Nevus pigmentosus has a certain relationship with individual’s poisoned skin color and other factors. 4. Gender factor: different scholars think that some studies show that women have more pigmented nevi than men. Acquired long pigmented nevus causes more, pigmented nevus generally do not need special treatment, easy to friction parts can be taken to surgical excision, if there is malignant change should be excised as soon as possible, and take for pathological examination.