Rheumatoid arthritis is what doctors call an autoimmune condition. It starts when your immune system, which is supposed to protect you, goes awry and begins to attack your body’s own tissues. It causes inflammation in the lining of your joints (the synovium). As a result, your joints may get red, warm, swollen, and painful.
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. Over time, RA can affect other body parts and systems, from your eyes to your heart, lungs, skin, blood vessels, and more.