A form of arthritis caused by too much uric acid build-up in your body. Gout often causes sudden pain and swelling in one joint, often the big toe or other joints in the feet. Uric acid is a natural substance that’s in your blood. Your kidneys filter uric acid, but if levels get too high or the kidneys can’t remove enough of it, urate crystals can form and settle into a joint, causing pain, swelling, and redness. Learn more.