There is a hard substance under the skin of the buttocks: the first consideration is lipoma. Lipoma is mostly benign, if there is no discomfort or the size is not more than 2cm and there is no sign of increasing, it can be removed without surgery, but attention should be paid to frequent observation. If the size is more than 2cm, and it grows bigger and bigger, or if there is pain when pressing on it, then it is better to have it surgically removed as soon as possible. Because some lipomas can be invasive and involve the muscles, surgical excision may need to remove the affected muscles as well. Secondly, it is considered to be caused by inflammation, which can be treated with antibiotics and physical therapy, such as infrared rays and microwave therapy, and the symptoms can be relieved in a day or so. If the swelling is already large, it is best to go to the hospital in time for consultation.