Pain in the left rib cage when you take a deep breath may be due to several reasons: 1. Be alert to the possible existence of rib-related injuries. If the left side of the thorax receives a direct impact, it may cause a contusion or fracture of the left rib cage. At this point, as soon as the patient takes a deep breath or coughs, there is a risk of pulling on the fracture end, which in turn leads to severe pain. In addition, it should be noted that in some elderly people or patients with severe osteoporosis, pathological fractures of the ribs, often caused by the patient doing breath-holding, or coughing or sneezing, may also produce the above-mentioned symptoms.2. It may be caused by intercostal neuritis, such as in the case of chickenpox-herpes zoster, which may involve the left intercostal nerve and subsequently lead to The pain around the rib cage is aggravated by deep breathing. 3. It may be due to pleural related lesions. If there are pleural adhesions, pleurisy or other diseases, the pleura will be pulled when the patient takes a deep breath, leading to severe pain, and sometimes the patient may be mistaken for the presence of pain in the left side of the rib cage.