Discomfort in the left side of the rib cage is due to several reasons: First, it may be due to long-term pressure here. For example, if the patient has a poor sitting or lying posture, it may lead to long-term compression and produce sterile inflammation in this area, and then the patient may feel uncomfortable in this area. Second, it may be caused by the cold here. If the patient is not sufficiently clothed here, or touches a cooler object, it may cause sterile inflammation here, leading to uncomfortable feelings. Third, it may be caused by osteoporosis. In patients with severe osteoporosis, there may be bony pain in this area. Fourth, it may be caused by lesions related to internal organs. For example, if the patient has coronary heart disease, pneumonia, adhesive pleurisy, gastritis and a series of other diseases, it may also cause discomfort here.