Moles, i.e. pigmented nevi, getting bigger and bigger may be caused by the growth of the pigmented nevus tissue itself, external stimulation, malignant lesions and other circumstances. 1. Growth itself: as the patient grows older, part of the nevus will increase with the growth of the body and other proportions, but the patient usually does not have any uncomfortable symptoms, but it may have some effect on the aesthetics. 2. External stimulation: prolonged friction, such as the neck, wrist often subject to friction parts, after friction can stimulate the growth of nevus pigmentosus, in addition, ultraviolet rays, radiation and other stimuli, will also lead to nevus pigmentosus is getting bigger and bigger. 3. Malignant lesions: when the nevus is getting bigger and bigger, it may be malignant lesions, when the nevus grows faster, becomes bigger in a short time, or the shape changes abnormally, or satellite foci appear in the surroundings, then we should consider the possibility of malignant lesions. It is recommended to go to the regular hospital in time to consult the doctor, to clarify the cause of the disease, and to carry out active treatment under the guidance of specialists, so as to avoid delaying the condition.