What causes bunions on feet?

A bunion or hallux valgus is a common foot deformity in which the big toe points towards the other toes. What causes bunions on feet? What are the bunion risk factors? With little explanation about its origins, you may be able to prevent bunion pain or delay its onset.

What causes bunions has still not been clearly identified. But we know that some background elements can contribute to the deviation of the big toe. Focus on all the causes of bunions with EPITACT^®, foot care specialist of hallux valgus!

Genetic causes of bunions

Studies show that hallux valgus is a family matter, repeated from one generation to the next⁽¹⁾. Compare with your mother’s feet! The genetic risk factor for bunions could be an excessive laxity of the body composition, or too severe expansions of tendon attachment^{(2, 3)}. Extreme high joint flexibility combined with a deficit of muscle balance are supposed to facilitate the deviation of the metatarsus.

Foot shape

The shape of your feet is Another important genetic background likely to cause a bunion. Three big categories can be distinguished:

• Greek foot shape: the second toe is longer than the first one (big toe);
• Egyptian foot shape: the big toe is longer that the four lesser toes, whose length decreases from the second toe to the little toe;
• Square foot shape: the first toe (hallux) and the second toe have the same length.

People with Egyptian foot shape seem to have higher probability to develop bunions than those with Greek shape or square shape. As the first toe is longer than the others, it is more exposed to physiological stress, which increases its lever effect⁽⁴⁾.

Bunion causes related to anatomy

It is not clear what causes bunions on feet but anatomical factors play an important role in the onset of hallux valgus. Flat feet contribute to foot pronation (off-centring outwards) and to axial rotation of the first metatarsal bone. Progressively, it increases the length of the first ray and the pronation of the big toe at the end of the walking movement.

The orientation as well as the anatomy of articular surfaces between the first metatarsal and the first phalanx can bring anatomical deviations and cause its deformity.

Another theory by Curvale and al.⁽⁵⁾ explains that when all predispositions for hallux valgus are present, the first phalanx then operates like a pushing element. So it would create inwards (varus) pressure on the metatarsal and finally accentuate the process. Though this may not be the main reason, this adds to the other causes of bunions.

Local muscle increase could be another cause of hallux valgus. The abductor hallucis muscle is the only one providing opposition to the metatarsus varus (inwards). The more the deformity progresses, the more the tendon of the abductor hallucis slips along the medial side of the first metatarsal head until it settles in this position. The deviation can continue without any physical opposition anymore as the abductor follows the modification of the tendon under the metatarsal head.

Shoes are major causes of bunions on feet

As far as what causes bunions to form, inappropriate footwear seems to be a major risk factor. For example, avoid wearing shoes with a high heel, chisel toe, dress and pointy shoes or narrow and tight footwear. The foot is squeezed and slowly deforms in order to find some room in the shoe. A narrow toe box contributes to increasing the deviation of the big toe. Moreover, they put pressure and rub against the bony bump which becomes very painful when walking.

Wearing poorly-fitting shoes is a risk factor for the onset or recurrence of bunions. Try to change your habits and choose shoes that fit you well! 

The causes of bunions on feet include the gender, weight and age

Doctors don't know exactly what causes bunions, however, there are some suspected causes related to gender, weight and age. 

The studies by Nguyen and al.⁽⁶⁾ on 600 patients in the USA point out that the bunion causes are different regarding men and women. It seems that wearing uncomfortable footwear combined with a low Body Mass Index (BMI) are determining factors in the development of a bunion in women. On the contrary, high BMI and flat feet are risk factors for bunions in men.

However, it would be interesting to place this theory in confrontation with the fact that mostly women develop a bunion on their feet, and this probability increases with age⁽⁷⁾.

You just have learned what causes bunions on feet. As you see, there are multiple bunion causes. It is clear that you can’t choose your genetic and anatomical background, however, choosing appropriate shoes belongs to you. Many footcare products help to prevent and reduce pain or correct the deformity. Have a look at the EPITACT^®bunion pads* and bunion correctors for day*, night* and sport*!

Read more about this foot problem in our next articles on how to diagnose a bunion and its nonsurgical treatments.

*These products are class I medical devices that bear the CE marking under this regulation. Carefully read the instructions before use. Manufacturer: Millet Innovation. 04/2023

For more details about this general and simplified approach, here are further sources:

⁽¹⁾Hannan MT, Menz HB, Jordan JM, Cupples LA, Cheng C-H, Hsu Y-H. High Heritability of Hallux Valgus and Lesser Toe Deformities in Adult Men and Women: Heritability of Hallux Valgus and Toe Deformities in Adults. Arthritis Care & Research. sept 2013; 65(9):1515‑21.

⁽²⁾Al-Saggaf S. Variations in the insertion of the extensor hallucis longus muscle. Folia Morphol (Warsz) 2003; 62:147–55.

⁽³⁾Gunal I, Sahinoglu K, Bergman RA. Anomalous tibialis posterior muscle as an etiologic factor in hallux valgus . Clin Anat 1994;7:21–5.

⁽⁴⁾Lelièvre J., Pathologie du pied. Paris : Masson, 1961

⁽⁵⁾Curvale G, Rocheweger A, Piclet-Legre B. Hallux valgus . Podologie. 1999; 27-080-A-30: p 6.

⁽⁶⁾Nguyen U-SDT, Hillstrom HJ, Li W, Dufour AB, Kiel DP, Procter-Gray E, et al. Factors associated with hallux valgus in a population-based study of older women and men: the MOBILIZE Boston Study. Osteoarthritis and Cartilage. janv 2010; 18(1):416.

⁽⁷⁾Nix S, Smith M, Vicenzino B. Prevalence of hallux valgus in the general population: a systematic review and meta-analysis. J Foot Ankle Res. déc 2010; 3(1):21.