Bunions develop when prolonged pressure on your big toe joint gradually pushes the joint out of alignment, causing the base of the toe to jut outward. About 19% of the global population has one, and the condition results from a combination of inherited foot structure, footwear choices, and the way your foot moves when you walk. Understanding what actually happens inside the joint helps explain why bunions tend to worsen over time and why some people are far more prone to them than others.
What Happens Inside the Joint
A bunion isn’t new bone growing on the side of your foot. It’s the existing joint shifting out of place. Your big toe is connected to your foot by the first metatarsal bone, and when that bone starts drifting inward (toward the center of your body), the tip of your big toe angles outward toward your smaller toes. The metatarsal head displaces to the inside of your foot, creating that visible bump at the base of your toe.
As this misalignment progresses, small bones called sesamoids that normally sit beneath the joint get left behind, ending up off-center relative to the metatarsal head. This makes the problem self-reinforcing: the more the toe drifts, the more the surrounding tendons and ligaments pull it further out of position. Over months and years, the big toe can rotate and crowd into the second toe, and the bump becomes more prominent.
Inherited Foot Structure
Your genes play a significant role, though scientists haven’t pinpointed specific genes responsible for bunions. What you inherit is a foot shape and mechanical structure that makes bunions more likely. Flat feet are one well-established risk factor. People with looser, more flexible ligaments (a trait called generalized hypermobility) also face higher risk, because that extra flexibility can compromise the stability of the joint complex where the first metatarsal connects to the midfoot, making it easier for the bone to drift out of alignment.
The familial pattern is hard to miss clinically. If your parents or grandparents had bunions, your foot structure likely shares the characteristics that set the stage for one. But inherited structure alone doesn’t guarantee a bunion. It creates vulnerability that other factors then exploit.
Footwear and Years of Pressure
Shoes don’t single-handedly cause bunions, but they can accelerate the process dramatically if your foot is already predisposed. The key culprit is a narrow toe box, the front section of a shoe that squeezes your toes together. High heels compound the problem by shifting your body weight forward onto the ball of your foot, increasing pressure on the big toe joint with every step.
This isn’t a quick process. Bunions result from extra pressure on the big toe joint sustained over years. The joint gradually shifts out of its natural position as your foot compensates for the chronic misalignment. This is why bunions rarely appear overnight. They’re the endpoint of thousands of hours of accumulated stress. If you already have risk factors like flat feet or loose ligaments, wearing tight, narrow shoes consistently over a decade or more can be the tipping point.
How You Walk Matters
The mechanics of your gait, specifically how your foot rolls and pushes off the ground, directly affect pressure distribution across the big toe joint. Overpronation, where your foot rolls excessively inward with each step, places uneven stress on that joint. Instead of pressure being spread across the forefoot, the inner edge bears a disproportionate load. Over time this asymmetric force encourages the first metatarsal to drift inward.
People with flat feet tend to overpronate more, which is one reason flat feet and bunions so often go together. But even people with a normal arch can overpronate due to muscle weakness, ankle instability, or simply the way their body is built from the hips down. Research has found that people with bunions tend to have different alignment measurements all the way up the leg, including a wider angle at the knee, suggesting that the forces contributing to bunions aren’t limited to the foot itself.
Who Gets Bunions Most Often
Women develop bunions at roughly twice the rate of men. A large meta-analysis covering over 186 million people found the prevalence was about 24% in women compared to 11% in men. Footwear habits explain part of this gap, since women are more likely to wear narrow, pointed shoes and heels. But hormonal and structural differences also contribute. Women tend to have greater ligament laxity, and hormonal changes during pregnancy can further loosen connective tissue in the feet, potentially accelerating joint instability.
Age is the other major factor. Bunions affect about 11% of people under 20, roughly 12% of adults between 20 and 60, and nearly 23% of people over 60. This steep increase reflects the cumulative nature of the condition. Decades of walking, combined with age-related loss of ligament strength and cartilage cushioning, push more joints past the threshold into visible deformity.
Medical Conditions That Raise Your Risk
Rheumatoid arthritis is a notable risk factor. The chronic inflammation it causes can weaken the ligaments and joint capsule around the big toe, making the joint less stable and more prone to drifting. People with rheumatoid arthritis who develop bunions often see related problems in the forefoot, including painful calluses that form as the foot compensates for the changing alignment. Early attention to foot changes in rheumatoid arthritis can help prevent these complications from compounding.
Osteoarthritis also contributes, though through a different mechanism. Rather than inflammation weakening ligaments, the breakdown of cartilage within the joint changes how forces are distributed, gradually altering alignment. Neuromuscular conditions that affect muscle balance in the foot can have a similar destabilizing effect on the big toe joint.
Why Bunions Get Worse Over Time
One of the frustrating aspects of bunions is that they’re progressive. Once the joint starts shifting, the mechanical forces acting on it change in ways that encourage further misalignment. The tendons that normally hold the big toe straight begin pulling at an angle, actively reinforcing the deformity. The joint capsule on the inner side stretches, while the outer side tightens. Each small increment of drift makes the next increment more likely.
This doesn’t mean every bunion inevitably becomes severe. The rate of progression varies widely depending on your foot structure, activity level, footwear, and body weight. Some people have a mild bump for decades that never causes significant pain. Others see rapid worsening, particularly if they continue wearing constrictive shoes or have an underlying inflammatory condition. Switching to wider shoes, using arch supports to correct overpronation, and strengthening the small muscles of the foot can slow progression, though they won’t reverse a bunion that has already formed.
Bunions in Children and Teens
Bunions aren’t exclusively an adult problem. Juvenile bunions can appear in adolescence, and they’re almost entirely driven by inherited foot structure rather than footwear. About 11% of people under 20 show some degree of bunion formation. In younger patients, the condition tends to be more directly tied to the shape of the metatarsal bone, the angle of the joint, or generalized ligament laxity. These bunions can progress through the growth years, so early recognition matters for managing them before the skeleton finishes developing.