Gout is a form of inflammatory arthritis that causes sudden, severe attacks of pain, swelling, redness, and tenderness in the joints, often starting in the big toe. It is characterized by the formation of needle-shaped crystals of uric acid in the joints, leading to inflammation and intense joint pain.

Gout is caused by elevated levels of uric acid (urate) in the body, a condition known as hyperuricemia. Uric acid is a waste product formed from the breakdown of purines, substances found in the body's tissues and various foods. Normally, uric acid is dissolved in the blood and excreted through the kidneys in urine. However, gout occurs when either the body produces too much uric acid or the kidneys do not remove enough of it, leading to excess uric acid that crystallizes in the joints.

These uric acid crystals trigger the immune system to cause inflammation, resulting in the characteristic symptoms of gout attacks. Not everyone with high uric acid levels develops gout, but factors such as diet (high in meat, seafood, and alcohol), genetics, age, sex (more common in males), certain medications, obesity, and other health conditions can increase the risk.

Thus, gout is a painful arthritis caused by uric acid crystal buildup due to an imbalance in production and excretion of uric acid in the body.