The causes of sudden swelling of the thumb are as follows: first, caused by injury and strain, due to acute trauma causing local injury, producing local bleeding, hematoma, and inflammatory reaction, resulting in symptoms of swelling. Chronic strain injury leads to cumulative local injury and inflammatory reaction, which affects local blood circulation and produces swelling symptoms. Second, aseptic inflammation of the thumb, including rheumatoid arthritis, gouty arthritis, etc., can cause swelling centered on the joint, often accompanied by pain. Third, infections, such as nail fungus or purulent dactylitis, can also cause swelling of the thumb, which may not be obvious in the early stages of pain, but can become severe as the condition progresses. Fourth, blood circulation is affected, such as cold in the thumb, prolonged pressure on the thumb or wrist, can also appear the symptoms of sudden swelling of the thumb, it is recommended to go to the hospital for detailed examination to clarify the diagnosis.