The causes of sudden swelling and pain in the thumb are as follows: 1. If there is stenosing tenosynovitis, it is recommended that rest be the main focus and avoid too much exercise, or you can take closed injection therapy. If it is not effective, surgery can be performed to release the tendon sheath. 2. If the pain is caused by local infection due to trauma to the thumb, it is usually accompanied by symptoms of local skin fever and should be treated with antibacterial drugs in a timely manner, commonly used antibiotics are cefixime dispersible tablets or amoxicillin capsules. If the swelling and pain caused by thumb trauma cannot be completely relieved after applying topical medication or taking oral pain medication, the patient should go to the hospital for X-ray examination as soon as possible, and if necessary, surgery should be performed according to the specific situation.