Gout is a type of arthritis caused by too much uric acid in the blood. When the concentration of uric acid gets too high, sharp urate crystals form. These crystals collect in the joints and cause swelling and intense pain. Gout attacks often come on suddenly and without warning and typically last 12 to 24 hours. The big toe is the most common joint affected, but gout attacks can also affect the ankles, knees, hands, and wrists. If left untreated, gout attacks occur with more frequency and can eventually cause permanent deformations and damage to joints.