The sudden swelling and pain of the bunion can be caused by the following reasons: first, gout, gout involving the bunion can appear suddenly swollen and painful, can be accompanied by redness of the skin, increased skin temperature, and in severe cases, gout stone formation, then we should take an early X-ray of the foot and blood uric acid tests to early diagnosis and treatment. Second, bunions, if due to excessive exertion or long-term wearing of high heels, resulting in extrusion of the bursa at the root of the big toe, inflammation can occur bunions, which can appear swollen and painful at the root of the big toe, and can be accompanied by significant activity restrictions, then early examination and foot x-ray examination should be taken to early diagnosis and treatment. Thirdly, infectious diseases, such as bacterial infection or tuberculosis infection, can also cause sudden swelling and pain in the big toe, and early blood tests and X-rays and CTs should be taken for early diagnosis and treatment.