A very painful hard lump on the buttocks is considered to be a skin boil. Skin boils are relatively common infections that are located in the deep surrounding tissue of the hair follicle. In the early stage of the disease, it will appear as a hard lump slightly protruding from the skin surface, with obvious pressure and pain. With further aggravation of the infection, there will be obvious redness, swelling, heat and pain, and even the formation of deep abscesses. The cause of skin boils may be related to lack of hygiene in addition to low immunity. Treatment is mainly anti-inflammatory, such as local topical mupirocin ointment, ichthyol ointment, oral amoxicillin capsule, roxithromycin capsule and so on. If the pus needs local incision and drainage. A very painful hard lump on the buttocks is recommended to consult a doctor in a timely manner, in the choice of medication, be sure to strictly comply with the doctor’s instructions to use.