How are bunions formed?

Many ways. The tendency to develop bunions is hereditary. Often poor biomechanical foot support can lead to malalignments and bunion deformity. Additional causes are excessively tight shoes, trauma, various neurological or developmental conditions. Weaing well fitting supportive shoes and orthotics can prevent progression of deformity. Surgery may be necessary in many cases.
Several things. Often times bunions are hereditary, but wearing narrow toed, tight shoes can speed up the formation. Injury or neuological dysfunction can cause bunions.
Many possible causes. Bunions may result from a variety of reasons such as genetics, trauma, biomechanical abnormalities, or as a result of narrow shoe gear.