Doctors still don’t know what causes rheumatoid arthritis (RA), but it is more common in people who smoke or have a family history of this disease. It can also be difficult to diagnose because many conditions cause joint stiffness and inflammation.
We know how the condition attacks the joints, but it is not yet known what triggers the initial attack. Some theories suggest that an infection or a virus may trigger RA, but none of these theories has been proven.
RA is an autoimmune condition. This type of condition causes the body's immune system to attack itself. Normally, your immune system makes antibodies that attack bacteria and viruses, helping protect your body against infection. If you have RA, your immune system sends antibodies to the lining of your joints, where instead of attacking harmful bacteria, they attack the tissue surrounding the joint.
When you have RA, antibodies attack the synovium, a membrane (thin layer of cells) that covers each of your joints. The synovium becomes sore and inflamed, which causes chemicals to be released and synovium to thicken. These chemicals can also damage bones, cartilage (the stretchy connective tissue between bones), tendons (tissue that connects bone to muscle) and ligaments (tissue that connects bone and cartilage). The chemicals gradually cause the joint to lose its shape and alignment and, eventually, can destroy the joint completely.
There is some evidence that RA can run in families. Your genes may be one factor in the cause of the condition. However, having a family member with RA does not necessarily mean that you will inherit the condition. Even an identical twin of someone with RA only has a small chance of developing it, so genes do not explain much of the risk.
RA is three times more common in women than in men. This may be due to the effects of oestrogen (a female hormone). Research has suggested that oestrogen may be involved in the development and progression of the condition. However, this has not been conclusively proven.
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Last reviewed: October 2017