On the left side of the back of the head, a lump grows. Pay attention to the size, hardness and mobility of the lump, and whether there is redness and pain. The masses at the back of the head are more commonly found in benign tumors such as powdery tumors, lipomas, and cysts. If the mass is small and there are no obvious symptoms, it can be left untreated and reviewed regularly. If the mass is larger, has obvious pain and other symptoms or grows faster, surgery is usually recommended to remove it. If the mass at the back of the head is red, swollen and painful, consider the possibility of boils caused by infection, and generally give anti-infection medication. If the mass is hard and cannot be moved, there is also the possibility of osteoma. If a lump grows on the left side of the back of the head, it is recommended to visit the neurosurgery department of the hospital and have a cranial CT and other examinations if necessary.