Sunken buttocks can be caused by thinness or excessive obesity, trauma or prolonged bed rest. 1. The body is thin: some people due to the natural body is relatively thin, subcutaneous fat is relatively small, the muscle is not very developed, so there will be the phenomenon of the buttocks side of the phenomenon of depression, generally if there is no special symptoms, do not worry too much. 2. The body is too obese: if the body is obese, the buttocks area has accumulated too much fat, fat tissue accumulation in the buttocks on both sides, fat distribution is not uniform, it will also make the buttocks look more depressed on both sides. 3. Trauma: If the buttocks area is traumatized, such as fall or burn, etc., which damages the muscles and ligaments on both sides of the buttocks, the local tissues may form a deformed healing in the process of recovery, which will result in the phenomenon of local depression. 4. Long-term bed-ridden: If you suffer from stroke or cerebral hemorrhage and other diseases, due to long-term bed-ridden, lack of activities, it is also easy to lead to muscle atrophy on both sides of the buttocks, resulting in the phenomenon of depression. There may be other reasons for the depression on both sides of the buttocks, and it is recommended to go to the regular hospital to complete the relevant examinations, make a clear diagnosis, and adopt the corresponding solutions according to the situation.