A hard lump with pain in the buttocks may be a localized infection, sebaceous cyst, hidden hair sinus and so on. 1. Local infection: local skin infection may appear local redness, swelling, heat and pain, and may also be manifested as a hard lump with pain, such as folliculitis, boils, carbuncle, etc.. 2. Sebaceous cysts: when the sebaceous gland opening keratinization, infection, etc. lead to poor sebum secretion, which causes sebum secretion in the sebaceous glands to gather, and then the formation of sebaceous cysts, there may be a localized hard nodule with pain. 3. Hidden hair sinus: it is the etiology is not very unknown, a kind of occurs in the sacrococcygeal intergluteal fissure of the soft tissues of a kind of chronic sinus tract or cyst, generally manifested as the internal hidden hair, can be repeated episodes, the main manifestation for the local redness, swelling, heat, pain and other acute inflammatory manifestations. It is recommended that if there are localized hard nodules with pain, consult a doctor as soon as possible to avoid delaying the condition.