A bunion is an enlarged bone on the side of the big toe that is angled outward. Depending on the severity of the bunion, the big toe may be angled mildly or sharply toward the other toes.
Bunions can be caused by:
Most bunions form as the big toe responds to abnormal pressure on foot joints. For example, your foot may roll excessively inward during walking. Over time, this stress may cause the big toe to move toward the other toes. This, in turn, pushes the big toe joint outward.
Bunions may develop along with inflammatory joint diseases such as osteoarthritis. They also often develop along with other foot problems, including hammertoes, corns, and calluses.