This causes the thin layer of cells (synovium) covering your joints to become sore and inflamed, releasing chemicals that damage nearby:

• bones
• cartilage – the stretchy connective tissue between bones
• tendons – the tissue that connects bone to muscle
• ligaments – the tissue that connects bone and cartilage

If rheumatoid arthritis is not treated, these chemicals gradually cause the joint to lose its shape and alignment. Eventually, it can destroy the joint completely.

Various theories of why the immune system attacks the joints have been suggested, such as an infection being a trigger, but none of these theories has been proven.

Possible risk factors:—

you may be born with a susceptibility to a disease, but it may take something in your environment to get the disease started.

Some of these factors have been identified. For example, in osteoarthritis, inherited cartilage weakness or excessive stress on the joint from repeated injury may play a role. Certain viruses may trigger disease in genetically susceptible people. Gender is another factor in some rheumatic diseases. Lupus, rheumatoid arthritis, scleroderma, and fibromyalgia are more common among women. This indicates that hormones or other male-female differences may play a role in the development of these conditions.

There are several things that may increase your risk of developing rheumatoid arthritis, including:

• your genes – there’s some evidence that rheumatoid arthritis can run in families, although the risk of inheriting it is thought to be low as genes are only thought to play a small role in the condition
• hormones – rheumatoid arthritis is more common in women than men, which may be because of the effects of the hormone oestrogen, although this link has not been proven
• smoking – some evidence suggests that people who smoke have an increased risk of developing rheumatoid arthritis