The common causes of left side rib swelling and pain are: left side chest wall trauma, costochondritis, left side lung infection, coronary heart disease and so on. 1. Left side chest wall trauma: If the left side of the chest has external impact, it can lead to soft tissue injury and fracture of the left side of the chest wall, which will result in swelling and pain in the left side of the rib cage. However, it is usually accompanied by localized redness, swelling, bruising, and pain aggravated by breathing. 2. Costal chondritis: When the rib cartilage is stimulated by bacterial infection or chronic non-infectious inflammation, it can lead to local inflammatory reaction and symptoms such as local redness, swelling, heat and pain. However, it is usually accompanied by pressure pain and swelling along the ribs. 3. Left side lung infection: If the left side of the lung is infected, the left side of the lung may show symptoms of swelling and pain at the ribs. However, it is usually accompanied by cough, sputum, fever, headache, dizziness and other symptoms. 4. Coronary heart disease: If there is insufficient blood supply in the coronary artery and other coronary heart disease, the left side of the chest may show symptoms of distension and pain, but the pain is usually presented with pressure, usually accompanied by chest tightness, dyspnea and other symptoms. There are many other causes of left rib swelling and pain, we need to consult a doctor in time, improve the examination, clear diagnosis, standardized treatment under the guidance of a physician to avoid aggravation of the condition.