Rib pain on both sides of the lower chest may be caused by both of the following: 1. It is endochondritis leading to aseptic inflammation of the endochondrium, which will result in local pressure pain. If the inflammation is severe, there will also be local redness, swelling, heat, and pain, skin flushing, and increased skin temperature. The pain will appear when deep breathing or thoracic exertion, or it will be aggravated on the basis of the original pain.2. It may be caused by local trauma, such as violent bruising of both ribs or crushing injury to the thorax. In this case, there is a clear history of trauma, and if the pain is severe, you must go to the hospital to check the chest X-ray to rule out fracture. If fracture is ruled out, it is usually a localized soft tissue contusion around the rib cage. The symptoms can slowly improve by resting and applying topical ointment.