Material provided by the National Institute of Arthritis and Musculoskeletal and Skin Diseases. You may visit their website at www.nih.com.

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Juvenile idiopathic arthritis is an autoimmune disorder, which means that the body mistakenly identifies some of its own cells and tissues as foreign.

The immune system, which normally helps to fight off harmful, foreign substances such as bacteria or viruses, begins to attack healthy cells and tissues. The result is inflammation—marked by redness, heat, pain, and swelling.

Doctors do not know why the immune system goes awry in children who develop JIA.

Scientists suspect that it is a two-step process. First, something in a child's genetic make-up gives them a tendency to develop JIA; and then an environmental factor, such as a virus, triggers the development of JIA.

To learn more about what causes rheumatoid arthritis, you should read our article on rheumatoid arthritis causes. It's addressing the adult-form of RA, but the concept is the same: something goes wrong in the body, and it starts to attack healthy tissue.  The medical community is still working on understanding the complexities of inflammatory arthritis.

Note: Juvenile idiopathic arthritis (JIA) was previously known as Juvenile rheumatoid arthritis (JRA).