Pain under the rib cage on the left side of the chest can be caused by several reasons: 1. Herpes zoster, in the early stages of herpes zoster, there can be pain at the lower rib cage on one side of the chest. After the incubation period of 1-2 weeks, there can be clusters of herpes, which should be diagnosed and treated early at the dermatology department; 2, intercostal neuralgia, intercostal neuralgia can also have pain at the lower intercostal nerve of one side of the chest, which should be diagnosed by early physical examination, early nerve nutrition and closed treatment; 3, dermatomal neuritis, when dermatomal neuritis can also have pain in the area of the dermatomal nerve distribution at the lower rib cage of one side of the chest, often as When there is a tumor or metastasis in the ribs, there can also be pain in the ribs, which should be diagnosed and treated by CT and ECT of the ribs.