The pain under the left side of the rib cage is mainly due to the following reasons: 1. the pain is caused by external wind and cold in daily life, or due to fatigue; 2. it is caused by some diseases, such as the most common chondromalacia, intercostal neuralgia and other conditions that lead to the occurrence of pain under the left side of the rib cage. In this case, we cannot exclude that there has been a strenuous exercise recently, which caused a strain on the muscles of the rib cage, thus causing the pain. The pain under the left side of the rib cage can be relieved by applying local heat and physical therapy, or by applying some topical fotarine ointment if the pain is severe. If you still can’t get relief, you should actively go to the hospital for a relevant examination to see what causes it, and then give targeted treatment.