The numbness under the left side of the rib cage may be caused by costochondritis and intercostal neuritis, and patients should consult a doctor in time to clarify the cause of the disease and then carry out the corresponding treatment. 1. Costal chondritis: more common in young adults, its onset may be related to infection, joint ligament injury, endocrine abnormalities and other factors, the patient will have the onset of numbness, pain and chest tightness and other symptoms, can be seen in the localized swelling, accompanied by pressure pain. 2. Intercostal neuritis: viral infection, trauma and other factors leading to the inflammatory reaction of the intercostal nerve, patients will have the onset of the site of the subcostal numbness, pain, mostly band-like distribution. Numbness under the left side of the ribs can also be seen in other diseases, it is recommended that patients go to the hospital in time to identify the cause of the disease, and active treatment.