There are many theories about how bunions develop, but the exact cause is unknown.
Factors likely include:
Inherited foot type, Foot injuries , Deformities present at birth (congenital)
conditions that affect both the nerves and muscles such as polio
Experts disagree on whether tight, high-heeled or too-narrow shoes cause bunions or whether footwear simply contributes to bunion development.
overpronation, having a low arch, or uneven weight-bearing in the foot or tendon that makes the toe joint unstable
Bunions might be associated with certain types of arthritis, particularly inflammatory types, such as rheumatoid arthritis.