The inflammation is caused by a build-up of uric acid. Uric acid, which your body produces when it’s breaking down purine, is usually filtered out by the kidneys. However, when your body is overproducing it, it can go unprocessed, thus resulting in a build-up, which then produces sharp, needle-like crystals that form in the body’s joints and surrounding tissue, usually in the big toe, but also in places like the ankles, knees, elbows, wrists, and fingers.