What causes RA?
RA is an autoimmune disorder. This means the immune system, which normally protects the body, actually causes harm. In RA, the immune system attacks the joint lining. The reason for this is unknown. Researchers believe it is a combination of genes (what is inherited from parents) and environment (for example, having infections from viruses or bacteria). Also, people who smoke or are overweight have an increased risk of developing RA.