RA is an autoimmune disease. There are some genetic factors; in addition smoking increases the risk of RA. The immune system normally protects us from infection by attacking germs such as bacteria and viruses. However, in people who develop autoimmune diseases, the immune systems is confused and overactive, and attacks our own body. This causes joint inflammation that will eventually damage the joint, cartilage and surrounding bones. The most commonly affected joints in RA are the small joints of the hands, wrists, ankles and feet; however any joints can be affected.