There is a bag in the buttocks that hurts when you touch it may be a sciatic nodule cyst, folliculitis, sebaceous cysts and other diseases. 1. Sciatic Nodal Cyst: It is because often sit on a hard stool, which leads to the soft tissue of the local sciatic node to be compressed or stimulated for a long time, so as to form a cyst. This cyst is relatively soft, the boundary is clearer, and when sitting or pressing will appear pain, you can choose surgical treatment. 2. Folliculitis: Folliculitis is a bacterial infection of the hair follicle that occurs as a purulent inflammation, which may also cause pain in the buttocks, and is generally treated with topical anti-inflammatory drugs, such as erythromycin ointment or topical mupirocin. 3. Sebaceous cysts: Sebaceous cysts are formed when the sebaceous glands are blocked, and secondary infections can also form enlarged lumps on the buttocks and are accompanied by pus production and inflammatory reactions in the surrounding skin tissues. Anti-infection treatment should be preferred in treatment, and surgery can be chosen for serious cases. Precautions: When there is a lump in the buttocks with pressure pain, you should go to the hospital for specialized treatment in time to prevent the delay of the disease.