A bulge on the back of the foot may be a subcutaneous cyst, and if the subcutaneous cyst does not subside on its own for a long time, it will need to be treated with surgical removal. It may be a tendon sheath cyst in the area, and the tendon sheath cyst may be slightly deeper. Some tendon sheath cysts may gradually subside, but if they do not subside for a long time, surgery is still required. It is possible that the subcutaneous hematoma is formed by trauma. If the subcutaneous hematoma is formed for a short period of time, cold towels or ice water should be applied in a timely manner to stop local bleeding, which can curb the continued expansion of the hematoma. If the hematoma has been formed for a long time, it can be treated with hot towels or heat therapy, or with oral medication to activate blood circulation and remove blood stasis.