Bunions form when the joint at the base of your big toe gradually shifts out of alignment, pushing the tip of the toe inward toward the smaller toes while the joint itself juts outward. This isn’t a growth of new bone in most cases. It’s the existing bone structure drifting apart over time, driven by a combination of inherited foot mechanics, footwear choices, and the repetitive forces of walking.
What Actually Happens Inside the Foot
Your big toe joint connects two bones: the first metatarsal (running through the midfoot) and the proximal phalanx (the first bone of the toe itself). In a bunion, the metatarsal drifts toward the inside of the foot while the big toe angles toward the outside, creating a V-shaped gap between the first and second metatarsals. The bump you see and feel is the head of that displaced metatarsal pressing against skin and shoe.
Once the shift begins, it tends to reinforce itself. The tendons that run along the top and bottom of the big toe start pulling at an angle rather than straight ahead, which gives them more mechanical leverage to keep the toe drifting sideways. That sideways tension stretches the ligaments on the inner side of the joint and compresses the outer side. Over time, the constant pull on the inner joint capsule stimulates new bone growth along the bump, while the small bones on the underside of the joint (the sesamoids) gradually slide out of position. The joint essentially remodels itself into a misaligned state that becomes harder to reverse the longer it persists.
Foot Shape You Inherit Matters Most
The single biggest factor behind bunion development is the structure of your foot, and that structure is largely inherited. According to MedlinePlus, the shape and mechanics of the foot, including how it distributes weight during walking, strongly influence bunion risk. Flat feet are one well-established inherited trait linked to bunions. A foot that pronates heavily (rolls inward with each step) places more stress on the inner edge of the big toe joint, accelerating the shift.
Bunions that appear in children or teenagers are especially tied to genetic joint deformities, though no specific genes responsible for adult-onset bunions have been identified yet. What runs in families isn’t the bunion itself but the foot architecture that makes one likely: a wider forefoot, a longer first metatarsal, looser ligaments around the midfoot, or a particular gait pattern. If your parents or grandparents had bunions, you’ve likely inherited some of those structural tendencies.
Joint Looseness in the Midfoot
One structural trait that gets particular attention is excess mobility in the joint where the first metatarsal meets the midfoot bones. When this joint is too loose, the metatarsal can drift more freely under the pressure of walking. A study in The Journal of Bone and Joint Surgery found that roughly 23% of feet scheduled for bunion surgery showed visible gapping at this joint on X-ray, a sign of instability. Interestingly, correcting the bunion itself often restored normal stability to that joint without needing a separate procedure to fuse it, suggesting the looseness and the bunion feed each other in a cycle.
How Shoes Make Things Worse
Shoes don’t single-handedly cause bunions in feet that aren’t predisposed to them, but they can dramatically speed up the process in feet that are. Narrow or pointed-toe shoes squeeze the toes together for hours at a time, applying constant lateral force on the big toe joint. High heels compound the problem by shifting body weight forward onto the ball of the foot, increasing pressure on exactly the area where the bunion forms.
This is one reason bunions are significantly more common in women than men. Population studies consistently find higher rates in women, and while some of that gap may reflect differences in connective tissue flexibility, decades of wearing narrow, heeled footwear play a clear role. Tight or stiff shoes also irritate an existing bunion, causing the overlying skin and the fluid-filled sac (bursa) cushioning the joint to become inflamed and painful, even when the underlying bone shift is modest.
Who Gets Bunions and When
Bunions are remarkably common. A large survey of over 2,600 adults in Turkey estimated hallux valgus prevalence at 54%, with rates climbing significantly in older age groups. While that figure reflects a broad clinical definition that includes mild cases, it illustrates how widespread some degree of big toe misalignment is, particularly as people age and the cumulative effects of weight-bearing take their toll.
People whose jobs involve prolonged standing or walking face higher risk. Nurses, teachers, factory workers, retail employees, and anyone spending most of the day on their feet accumulate more repetitive loading through the forefoot. Combined with unsupportive footwear, years of occupational standing can turn a mild structural predisposition into a visible, painful bunion.
Inflammatory Arthritis Adds Another Layer
Rheumatoid arthritis creates bunions through a different pathway. Rather than gradual mechanical drift, the autoimmune inflammation erodes cartilage and bone within the joint itself. According to the Arthritis Foundation, this erosion causes the toe to shift or dislocate, crowding the smaller toes and pushing the big toe joint outward. Bunions related to rheumatoid arthritis tend to progress faster and can be more severe because the joint damage is driven by ongoing inflammation rather than simple mechanical stress.
What Happens If a Bunion Keeps Progressing
Most people with bunions never develop serious complications. The bump may be cosmetically bothersome or mildly uncomfortable in certain shoes without ever causing functional problems. But in cases that go untreated and continue to worsen, secondary issues can develop.
The most common complication is displacement of the second toe. As the big toe angles further sideways, it pushes underneath or over the second toe, which can develop its own deformity (hammertoe) as it’s forced upward and out of position. Arthritis in the big toe joint itself is another consequence of long-term misalignment, as the cartilage wears unevenly under abnormal loading. Bursitis, the painful inflammation of the fluid sac over the bump, tends to flare with shoe pressure and can become a recurring problem. Corns and calluses form where the shifted toes rub against each other or against the inside of shoes.
Slowing the Progression
Because the underlying cause is structural, bunions don’t reverse on their own and no exercise or splint can push the bones back into perfect alignment once they’ve shifted. What you can control is how fast the process continues. Switching to shoes with a wide toe box gives the toes room to spread naturally and reduces the sideways force on the joint. Avoiding heels over two inches keeps weight distributed more evenly across the foot. Cushioned pads over the bump reduce friction and bursitis flare-ups.
Custom or over-the-counter arch supports can help if flat feet or overpronation are contributing factors, by controlling how much the foot rolls inward with each step. Toe spacers worn at home may relieve discomfort by temporarily restoring some separation between the first and second toes, though they won’t change the bone position permanently. For bunions that cause persistent pain, limit activity, or lead to secondary toe problems, surgical correction is the only option that actually realigns the bones. The specific procedure depends on the severity of the angle and which joints are involved, but the goal is always the same: straighten the metatarsal, reposition the sesamoids, and tighten the stretched ligaments so the joint holds its corrected position.