Over-pronators who have abnormal motions with their first metatarsal bones are likely candidates for bunions
"Bunion" is a term loosely used to describe pain in and around the big toe joint. In medical terminology, a bunion is a bursa, or fluid-filled sac, that occurs in a location not normally occupied by a bursa. In the foot, bunions occur over the first metatarsal head (big toe joint) and the fifth metatarsal head. They occur as a result of pressure and friction from shoes over metatarsal heads that are enlarged and prominent. When irritated by tight or ill-fitting shoes, bunions will become red, swollen and painful. Some people have "bunions" and pain which comes from inside the big toe joint and may be caused by trauma, arthritis, or abnormal foot mechanics that leads to wear-and-tear arthritis. Individuals with this have painful and decreased motion, or no motion at all at their big toe joints. Some bunions are caused by arthritis and trauma, but most are due to heredity. Actually, people are not born with bunions, but they inherit the foot type which allows bunions to occur. Over-pronators who have abnormal motions with their first metatarsal bones are likely candidates for bunions. Depending on the structure of the big toe joint, some people get arthritic big toe joints with decreased and/or painful motion, and others get bunions where the first metatarsal bone splays out and the big toe drifts over (hallux abducto valgus), creating a bump that may become irritated by shoes.
If you have decreased or painful motion, use shoes with stiffer soles as they reduce joint motion and pain. For those with hallux abducto valgus, avoid pointed toe shoes and use shoes with wide forefeet and soft uppers. Also, I find a device called a ball and ring stretcher is very effective in stretching shoes to accommodate bunions and hammer toes. Your local shoe repair shop should be able to do this for you. If your "bunion" is caused by abnormal pronation, orthotics will control the motion that leads to the deformity and should be used.