Gout is a form of inflammatory arthritis that results from an excess of uric acid (a chemical that is created as the body breaks down certain substances in food called purines) in the blood. In people with gout, uric acid crystallizes in the joints causing painful attacks in the affected body part - often, initially, a big toe. Other joints that may be affected include the ankle, foot or knees, and in severe cases, the wrists, elbows and fingers. In gout, as in CPPD (see below), as white blood cells envelop the crystals, chemicals are released that prompt the inflammatory process. Uric acid can also crystallize as kidney stones and can damage the kidneys. People suffering from attacks of gout often need lifelong medications to prevent excess uric acid formation.