Swelling of the thumb head may be related to tenosynovitis, rheumatoid arthritis and thumb contusion. 1. Tenosynovitis: repeated mechanical friction causes strain on the tendon sheath of the thumb, which produces a localized chronic inflammatory reaction, resulting in symptoms of swelling and pain. 2. Rheumatoid arthritis: an immune disease caused by heredity, infection, environment and other reasons. There is pain and swelling of the thumb and symptoms of morning stiffness. 3. Thumb contusion: it may be caused by a sudden external force, the pain may not be very obvious at the time of injury, and after a period of time, there is swelling of the soft tissues of the thumb muscles and limitation of activities. Thumb swelling can also be seen in other causes, it is recommended to consult a doctor in a timely manner, follow the doctor’s instructions for relevant examinations, with the help of the doctor to clarify the cause, and targeted treatment or treatment.