The primary cause of bunions is genetics: inherited foot structure and faulty foot mechanics can make you more likely to develop them. For example, having low arches, flat feet, or a tendency to overpronate (when your feet roll inward when you move, causing them to overly flatten) can exert pressure that leads your big toe to curve toward your second toe.
Medical conditions like rheumatoid arthritis can increase the likelihood of developing bunions. But by far the biggest contributing factor is poorly fitting shoes, particularly those with a narrow, pointed toe that force your toes into an unnatural position.
Anyone can develop a bunion, but they’re 10 times more common in women because of their lighter bone structure and tendency to wear tight, narrow shoes that squeeze the toes together. This makes it more likely for a bunion to develop and for an existing bunion to worsen. High heels, which tip the body’s weight forward and place unnecessary pressure on the joints, exacerbate the problem.
Bunions may start out small, but they usually progress over time—which is why early treatment is so important. Because the metatarsal phalangeal (MTP) joint flexes with every step, the bigger the bunion gets, the more painful and difficult walking can become. As the bunion gets worse, permanent degenerative changes that occur as a result also increase, Dr. Levine explains. For instance, the MTP joint at the base of the big toe can become stiff and increasingly hard to bend—something known as hallux rigidus.
