The common causes of swelling under the right side of the rib cage are as follows: 1, strain of intercostal muscle: often due to prolonged ambulatory work, improper sitting posture, such as often twisting the waist and sitting for a long time, it is easy to cause an imbalance in the force of bilateral intercostal muscle, which often leads to strain of one side of the intercostal muscle, which can be manifested as soreness and pain in one side of the rib area and rib cage; 2, liver disease: swelling and pain under the right side of the rib cage may occur due to chronic liver disease, chronic hepatitis, patients should actively carry out liver function tests as well as liver CT, so as to observe the liver morphology; 3, intestinal flatulence: patients will experience full abdominal distension and pain, which can sometimes be located in the right quarter rib area.