RA causes the body’s immune system to attack healthy tissue in the joints. In people with RA, the immune system mistakenly attacks joints instead of fighting off foreign bacteria, viruses, or other harmful substances that may enter the body. This causes inflammation in the joints and can cause pain and swelling over time. For many people, RA can affect other parts of the body, including your eyes, kidneys, heart, lungs, liver, skin, blood vessels, or nervous system.