Buttocks mostly refers to the buttocks, once you sit down on the buttocks uncomfortable possible reasons are overwork, trauma, sacroiliac arthritis, pyriformis syndrome and so on. 1. Excessive exertion: because of sedentary, strenuous exercise, long time running, etc., resulting in a large accumulation of lactic acid, can appear discomfort, is a normal phenomenon. 2. Trauma: because the buttocks hit the ground when falling, falling from a high place, etc., resulting in skin and subcutaneous tissue damage or even sacral fracture of the buttocks, when sitting down the buttocks are squeezed, pain and discomfort can occur. 3. Sacroiliac arthritis: because of sedentary, trauma, prolonged weight-bearing, etc., causing aseptic inflammation of sacroiliac joints, common symptoms include pain in the buttocks and lumbar back, and difficulty in activities. 4. Piriformis syndrome: due to trauma, long-term drug injection, etc., causing degeneration and contracture of the piriformis muscle, compression to the sciatic nerve, pain and discomfort in the buttocks can occur. Once you sit down on the buttocks uncomfortable causes more, but also may be with ankylosing spondylitis, femoral head necrosis, hip synovitis, hemorrhoids, perianal abscess and other diseases, if the symptoms continue to be unrelieved, it is recommended to consult a doctor in a timely manner, to clarify the cause of the disease, targeted treatment.