Juvenile arthritis is a type of arthritis that happens in children age 16 or younger. It causes joint swelling, pain, stiffness, and loss of motion. It can affect any joint, and in some cases it can affect internal organs as well. One early sign of JA may be limping in the morning. Symptoms can come and go. Some children have just one or two flare-ups. Others have symptoms that never go away. JA causes growth problems in some children. No one knows exactly what causes JA. Scientists do know it is an autoimmune disorder, which means your immune system, which normally helps your body fight infection, attacks your body’s own tissues. JA can be hard to diagnose. Your health care provider may do a physical exam, lab tests, and x-rays. Medicines and physical therapy can help maintain movement and reduce swelling and pain.