There are several reasons for the pain in the upper left back: first, localized inflammation of the skin, such as sebaceous cysts or folliculitis, may cause local inflammatory reaction and pain. Second, the muscles under the skin are strained or strained, as well as cold, may form a local inflammatory metabolite gradual accumulation, resulting in peripheral nerve stimulation, there will be pain. Third, due to the fracture of the scapula and the ribs in the back, the fracture broken end will produce inflammatory edema, stimulate the surrounding tissues will appear pain. Fourth, there may be pleurisy, because after the inflammation of pleurisy, when you breathe heavily and cough, there will also be pain in this position. Fifth, duodenal bulbous posterior ulcer, usually during fasting, due to gastric acid stimulation of the ulcer site, there will also be pain in the left upper back.