Gout is a type of arthritis that is caused by the build-up of uric acid in the blood. When too much uric acid accumulates, it can form crystals in the joints, leading to inflammation and pain. The most common symptom of gout is a sudden, severe attack of pain in the joints, often in the big toe. Other symptoms can include swelling, redness, and warmth in the joint. Gout can usually be treated with medication and lifestyle changes.