A bunion, known technically as hallux valgus, is a bony bump on the side of the foot at the base of the big toe. Bunions develop slowly as pressure on the joint at the base of the big toe causes the toe to move out of place, leaning inward toward the second toe. Because this joint carries a lot of weight during activities like standing and walking, bunions can cause foot pain, stiffness, redness, and swelling. Calluses may form where the big toe and second toe rub together or on the ball of the foot. Unless they are treated, bunions get worse over time, and it may become difficult to wear regular shoes or walk without pain. Bunions can occur in one or both feet.

In most cases, bunions develop in adulthood. Rarely, children may be born with bunions (known as congenital hallux valgus) or develop them later in childhood (juvenile or adolescent hallux valgus).

Bunions are a very common foot disorder, affecting about a third of adults in the United States. The prevalence of bunions increases with age. They are more common in women than in men, likely because of differences in foot anatomy, footwear, and genetic influences.

The causes of bunions are unclear, although scientists suspect that both inherited and lifestyle factors contribute to their development. Studies suggest that congenital and juvenile hallux valgus tend to be related to joint deformities with a genetic cause. Little is known about the genetic contribution to bunions that occur later in life, and no specific genes involved in the development of bunions have been identified.

For bunions that appear in adulthood, inherited factors related to the shape and structure of the foot and the way the foot moves (foot mechanics) likely influence a person's risk of developing the condition. It has long been suggested that wearing ill-fitting shoes are another significant risk factor, specifically shoes that are too tight, shoes with high heels, or shoes with a narrow toe box. Research suggests that poorly fitting shoes probably do not cause bunions, but they may make bunions develop earlier or worsen more quickly in people with an underlying susceptibility.

Other risk factors for bunions include inflammatory diseases (such as rheumatoid arthritis), osteoarthritis, and flat feet (pes planus). Bunions are also a feature of several rare genetic syndromes that affect bone development, including Chitayat syndrome and fibrodysplasia ossificans progressiva.

Bunions are a complex condition without a clear pattern of inheritance. Many affected individuals have multiple family members who are also affected. The risk of developing bunions is greater for first-degree relatives of affected individuals (such as siblings or children) as compared to the general public.

When bunions occur as part of a genetic syndrome, this feature follows the inheritance pattern of the syndrome.

Prevention

To prevent bunions, people are advised to wear comfortable, flat shoes. If there’s enough room for the front of the foot, there’s less pressure on the toes and the ball of the foot. Other advice includes walking barefoot in order to strengthen the foot muscles and allow the feet and toes to be in their natural position. Some doctors recommend using orthopedic shoe inserts (insoles). But there’s not a lot of research on how well this can prevent bunions.

Treatment

Bunions can get worse over time. Treatment is only needed if they cause problems. The most suitable treatment will depend on a number of factors, including the symptoms, the type of deformity, and whether the person has other medical conditions such as rheumatoid arthritis, diabetes or vascular (blood vessel) disease.

There are various conservative (non-surgical) treatments that aim to relieve the symptoms of bunions: Only a few good-quality studies have looked into how well they work, though.

• Splints: These toe-spacers or toe-supports are used to keep the big toe in a normal position. The aim is to relieve the symptoms and slow down the progression of the bunion – although it’s not clear whether this is possible. They can’t correct the misalignment. Splints are typically used at night.
• Well-fitting shoes: People are advised to wear flat shoes that give the toes enough room. If the toes or big toe joint hurt, bunion pads can be used. If the middle part of the foot hurts (metatarsalgia), the toes can be cushioned or supported using shoe inserts or wearing special “rocker bottom shoes.” Walking barefoot as much as possible is also recommended.
• Physical therapy (physiotherapy): Special exercises can be done to try to strengthen and stretch the foot muscles.
• Painkillers: These may include non-steroidal anti-inflammatory drugs (NSAIDs) in the form of tablets or an ointment. Due to potential side effects, tablets should only be used over a short period of time.

But only a few studies have looked into these treatments. They suggest that measures such as physical therapy, wearing well-fitting shoes and using splints can't really provide relief.

If the symptoms are severe and no other treatment helps, surgery may provide relief. Surgery is the only way to treat the cause of the symptoms, by correcting the misalignment. But there’s no guarantee that surgery will make the symptoms go away completely, and it can have side effects.