A bunion is a bone deformity caused by an enlargement of the joint at the base and side of the big toe (metatarsophalangeal joint). Bunions form when the toe moves out of place. Over time, the movement of the big toe angles in toward the other toes, sometimes overlapping a third toe (known as Hallux Valgus).
The growing enlargement or protuberance then causes more irritation or inflammation. In some cases, the big toe moves toward the second toe and rotates or twists, which is known as Hallux Abducto Valgus. Bunions can also lead to other toe deformities, such as hammertoe.
Because they are bone deformities, bunions do not resolve by themselves. Depending on the size of the enlargement, misalignment of the toe, and pain experienced, bunion surgery, known as a bunionectomy, may be advised to remove the bunion and realign the toe.