A little pain under the ribs on the left side of the body is associated with diseases such as chronic gastritis, acute pancreatitis, and inflammation of the rib cartilage. Below the left rib cage is the stomach, and in patients suffering from chronic gastritis, stomach acid can cause damage to the gastric mucosa, leading to spasm of the stomach wall, which can cause localized pain. The main part of the pancreas is on the left side of the abdomen. When the pancreas becomes inflamed, the inflammatory cells cause irritation to the pancreas, thus causing pain in the area where the pancreas exists. Patients will also have pain under the left rib cage as the main manifestation, as well as nausea, vomiting and diarrhea. Some people experience pain under the left rib cage, due to costochondritis. The main cause of costochondritis is a sterile inflammation of the ligaments of the body caused by holding the same position for a long time or repeating a certain action repeatedly, which causes pain in the ribs as the main symptom.