Moles on the back are getting bigger and bigger, which may be caused by their own growth, external stimulation, or cancerous changes of pigmented moles. 1. Growth of the mole itself: there is a natural growth phenomenon of the mole, it will gradually increase with the metabolism and age of the person, and the patient has no self-conscious symptoms, which is a normal phenomenon. 2. External stimulation: If it is often rubbed, it may gradually increase in size, or be stimulated by ultraviolet rays or radiation, etc., which will also lead to bigger and bigger moles on the back. 3. Cancer of pigmented nevus: if the nevus on the back suddenly becomes bigger in a short period of time, with irregular boundary and accompanied by pain, itching, or even broken and oozing, it may be the phenomenon of cancer of pigmented nevus. It is suggested that patients should go to the hospital in time, and under the guidance of doctors, relevant examination should be carried out, and targeted treatment should be taken according to the specific examination results of patients.