Rheumatoid arthritis is a chronic inflammatory disorder that can affect more than just your joints. In some people, the condition can damage a wide variety of body systems, including the skin, eyes, lungs, heart and blood vessels. An autoimmune disorder, rheumatoid arthritis occurs when your immune system mistakenly attacks your own body's tissues. Unlike the wear-and-tear damage of osteoarthritis, rheumatoid arthritis affects the lining of your joints, causing a painful swelling that can eventually result in bone erosion and joint deformity. The inflammation associated with rheumatoid arthritis is what can damage other parts of the body as well. While new types of medications have improved treatment options dramatically, severe rheumatoid arthritis can still cause physical disabilities. Rheumatoid arthritis (RA) happens when your body's defenses – your immune system – targets your joint linings. RA affects joints on both sides of the body, such as both hands, both wrists, or both knees. This symmetry helps to set it apart from other types of arthritis. It can also affect the skin, eyes, lungs, heart, blood, or nerves. Some people appear to have genetic factors that make it more likely. One theory is that bacteria or a virus triggers RA in people who have this genetic feature. In RA, the immune system’s antibodies attack the synovium, which is the smooth lining of a joint. When this happens, pain and inflammation result. Inflammation causes the synovium to thicken. Eventually, if left untreated, it can invade and destroy cartilage — the connective tissue that cushions the ends of the bones. The tendons and ligaments that hold the joint together can also weaken and stretch. The joint eventually loses its shape and configuration. The damage can be severe.