Swelling and pain in the thumb can have the following causes: First, tenosynovitis, when the thumb has stenosing tenosynovitis, there can be swelling and pain in the metacarpophalangeal joint of the thumb, usually on the palmar side, which should be investigated early, diagnosed early, and treated with closure and surgery early. Second, gout, when the gout involves the thumb joint, there can be swelling and pain in the thumb, which can be accompanied by skin redness and swelling, increased skin temperature, and the formation of gout stones, then it is necessary to check the blood uric acid and take an X-ray of the hand for early diagnosis and treatment. Third, rheumatism and rheumatoid rheumatism can also present with swelling and pain in the thumb joint. Fourth, osteoarthritis, when the metacarpophalangeal joint of the thumb has osteoarthritis, it can appear swelling and pain of the thumb, then it is necessary to take an early X-ray of the hand for early diagnosis and treatment.