Pain under the left bunion can be caused by the following: first, toe neuritis and toe neuroma. When there is inflammation or tumor in the toe nerve of the bunion, there can be pain under the bunion, which should be diagnosed by early medical examination, early nerve nutrition and physical therapy, and if necessary, surgery. Second, bunion tumors or infections, when there is soft tissue or joint tuberculosis, bacterial infection, or tumor growth in the lower part of the big toe, there can also be pain under the big toe, which should be diagnosed by early physical examination, early MRI of the big toe, and if necessary, blood tests for further examination. Thirdly, inflammation of the joint, when the joint of the big toe has rheumatism, rheumatoid or arthritis, it can also have pain under the big toe, then it is necessary to take X-rays at an early stage for diagnosis and early treatment.