Rheumatoid arthritis, known as RA, is the other most common type. The end result is the same—stiff, achy joints—but rheumatoid arthritis is an autoimmune disease. The body's immune system attacks its own joints, causing their lining to swell and hurt. RA is almost 3 times more likely to strike women than men, and it tends to first occur between ages 25 and 50. Rheumatoid arthritis often affects the same joints on both sides of the body. Hands, wrists, feet, knees, ankles, shoulders, and elbows can be affected. Regular arthritis tends to most affect weight-bearing joints, such as the knees and hips; whereas rheumatoid arthritis more frequently impacts the entire body: both large and small joints, as well as other organs.