Left side rib pain is usually caused by spontaneous pneumothorax, costochondritis or intercostal neuritis. 1. Spontaneous pneumothorax: long and thin people are prone to spontaneous pneumothorax during strenuous activities, which is characterized by chest pain and dyspnea. 2. Costochondritis: Costochondritis can be caused by viral infections, soft tissue strains of the intercostal muscles, etc. It can cause pain in the ribs next to the sternum, and it can also be caused by poor dietary habits. 3. Intercostal neuritis: Intercostal neuropathy due to herpes zoster virus infection, spinal lesions, etc. can also cause rib pain. Therefore, on the basis of attention to rest, you can also take oral medication to relieve the symptoms, if the symptoms can not be relieved after the use of medication, you need to consult a doctor in time, in order to clarify the diagnosis and treatment.