A hard lump on the right side of the abdomen along the lower part of the rib cage may be caused by rib ectropion, rib fracture, sebaceous cyst and other diseases. 1. rib ectropion: when breathing, due to the strenuous movement of the abdomen, it will cause rib ectropion, which will result in a hard lump on the right side below the rib cage. 2. Rib fracture: with age, the elasticity of the ribs will decrease with time. In case of chest injury, a broken rib on the right side will cause deformation of the right side of the ribs or a hard lump under the right side of the ribs, and there will be localized severe pain and restriction of breathing. 3. Sebaceous cysts: Obstruction of the excretory ducts of sebaceous glands tends to fill up their contents and form retention cysts on the surface of the skin, or a hard lump under the right rib cage if it is in the right abdomen. If the symptom of a hard lump on the right side of the abdomen along the lower part of the rib cage persists without relief, prompt medical treatment is needed.