Swelling and pain in the thumb may be caused by trauma, gout, rheumatoid and rheumatoid arthritis, tenosynovitis and other reasons. 1. Trauma: the thumb is hit by violence, causing local tissue damage and swelling. 2. Gout: Uric acid in the blood is relatively high, when gout involves the thumb joint, it can also cause swelling and pain, usually accompanied by skin warming, and even the formation of gout stones. 3. Rheumatoid and rheumatoid arthritis: can also lead to swelling and pain in the joints of the thumb. 4. Tenosynovitis: Tenosynovitis in the narrow part of the thumb can cause swelling and pain in the joint. There may be other causes, it is recommended to consult the doctor for examination and treatment as soon as possible to avoid delay.