What is rheumatoid arthritis? Rheumatoid arthritis (RA) is a chronic (long-lasting) disease that mostly affects joints, such as the wrist, hands, feet, spine, knees, and jaw. In joints, RA causes inflammation that leads to: Pain. Swelling Stiffness. Loss of function. Normally, the immune system helps protect the body from infection and disease. RA may cause you to feel unusually tired, to have occasional fevers, and to have a loss of appetite.