The cause of thumb swelling may be related to cold, bad posture, trauma, infection, rheumatoid arthritis and other factors. 1. Cold or bad posture: If the thumb is cold, or under pressure for a long time or in a bad posture, it can lead to the local blood circulation of the thumb being affected, which will lead to the symptom of swelling of the thumb. 2. Trauma: due to the role of external forces, such as extrusion, resulting in thumb injury or strain, so that the injured part of the bleeding, hematoma, which is manifested as swelling and pain in the thumb. 3. Infection: thumb due to small puncture wounds, scratches, reverse peeling, or nail trimming too much, thus leading to tenosynovitis, gingivitis, purulent dactylitis, etc., can appear thumb swelling, pain and other symptoms. Prolonged exposure to cold or exertion may aggravate the symptoms. 4. Other diseases: such as rheumatoid arthritis, gout, can be manifested as swelling of the thumb, and there is pain, restricted movement and other manifestations. Swelling of the thumb may also have other causes, it is recommended to go to the hospital in a timely manner, improve the examination to determine the cause of the disease, and then give targeted treatment or therapy.