Pain at the ribs under the left chest may be caused by trauma, pleurisy, angina pectoris, intercostal neuritis, lung cancer, neurosis and so on. 1. Trauma: the rib cage of the left chest is subjected to trauma such as collision, extrusion, pulling and contusion, which leads to skin of the chest wall, subcutaneous tissue or even fracture of the rib cage and tissue damage in the chest cavity, and so on, so there will be pain at the rib cage. 2. Pleurisy: pleural infection leads to inflammatory lesions such as oozing, bleeding, adhesion, etc. The friction between pleura and ribs increases, so there is pain in ribs. 3. Angina pectoris: emotional excitement, excessive activities increase myocardial oxygen consumption, which further aggravates myocardial ischemia caused by coronary artery stenosis, and thus pain in the ribs occurs. 4. Intercostal neuritis: Inflammatory lesions of intercostal nerves due to infection, trauma and other factors, resulting in radiating pain distributed along the intercostal space, and pain in the rib cage will occur when the left chest is involved. 5. Lung cancer: the left lung cancer invades the chest wall in the middle and late stages and stimulates the nerves of the chest wall, resulting in pain at the ribs. 6. Neurosis: there is no organic lesion, which may be related to subjective strange feeling. The pain at the rib cage under the left chest may be related to many factors, and it is recommended to consult a doctor for clear diagnosis and timely symptomatic treatment.