Sudden pain under the right breast in women may be caused by the following reasons: 1. Injuries, such as direct violent blows to the area or long-term pressure due to a hard bra, can cause a series of sterile inflammation or other injuries, which can lead to pain. 2. 3. due to costochondritis, which is often caused by prolonged pressure, cold or trauma to the costal cartilage, leading to aseptic inflammation and resulting in sudden pain. 4. due to breast-related lesions, where lobular hyperplasia or breast cancer are present. 5. Sudden pain may be caused by lesions inside the chest cavity, if a pneumothorax or pleural adhesions suddenly appear.