The possible causes of pain inside the rib cage under the right breast are as follows: 1. breast enlargement, often manifested as pinprick-like pain or swelling before the onset of menstruation, which can mostly be relieved by itself after the menstrual period. 2. peptic ulcer, manifested as periodic pain associated with eating, which can be accompanied by acid reflux and heartburn. 3. pleurisy, often with acute onset, manifested as chest pain, cough, chest tightness and shortness of breath, etc., chest pain caused by inflammation of the wall pleura, mostly during deep breathing or coughing. 4. Intercostal neuralgia, mostly caused by thoracic spinal tuberculosis, fracture or spinal tumor and other lesions involving the intercostal nerve, mostly manifests as radiating pain from the back along the intercostal bone to the anterior chest wall, which is aggravated by deep breathing, coughing and sneezing. 5, intercostal chondritis, mostly of unknown etiology, manifests as chest pain, which is obvious when pressing locally, and no abnormal changes in the skin of the chest wall. 6, cholecystitis, often manifests as chest pain, coughing, chest tightness and shortness of breath. The pain can be radiated to the back of the right shoulder. Ultrasound or CT can show enlarged gallbladder, thick wall edema, etc.