The discomfort but no pain in the left upper abdomen may be caused by dietary factors, functional dyspepsia, gastritis, spontaneous pneumothorax and other reasons. 1. Dietary factors: eating too much gas-producing food, such as soy products, carbonated beverages, potatoes, sweet potatoes, etc., these foods are digested and decomposed in the stomach to produce more gas, so the left epigastric abdominal distension and discomfort. 2. Functional dyspepsia: stomach peristalsis is slow, food can not be emptied in a timely manner, resulting in the left upper abdomen bloating discomfort with nausea, loss of appetite and other symptoms. 3. Gastritis: patients with gastritis may experience epigastric distension, nausea and vomiting during the attack period, but the pain is not very intense or no pain. 4. Spontaneous pneumothorax: During the attack period, there may be symptoms such as obvious stuffiness in the left upper abdomen and dyspnea. The discomfort in the left upper abdomen involves more causes, it is recommended to consult a doctor in time to clarify the cause of the disease and follow the doctor’s instructions for treatment.