The causes of pain on the left side of the back below the ribs include costochondritis, intercostal neuralgia, lumbar disc herniation, kidney disease and so on. 1. Costal chondritis: when being hurt by external force or keeping a bad posture for a long time, the soft tissues around the costal cartilage can be damaged, resulting in inflammation of the costal cartilage, which leads to localized swelling and pain, and the pain can be aggravated when pressing. 2. Intercostal neuralgia: pain caused by inflammation of the intercostal nerve, the pain is distributed along the intercostal nerve, strip-like, stinging or burning pain. When herpes zoster virus infection is caused, herpes zoster can be seen in clusters on the surface of the skin. 3. Lumbar intervertebral disc herniation: If long-term chronic strain injury prompts lumbar intervertebral disc herniation and deformation, and if the disc protrudes to the left, the protruding part can make the blood vessels and nerves be compressed, which will make the left side of the back below the ribs to appear the symptoms of pain. 4. Kidney disease: such as kidney stones, can make the lesion around the tissue structure and peripheral nerves are stimulated, and then appear in this position of the pain. The left side of the back below the ribs is very painful can also be seen in other diseases, it is recommended that the patient to the regular hospital in a timely manner, in order to avoid delaying the condition.