Heel spurs are caused by repetitive stress on the heel bone. Over months or years, the constant pull of muscles and ligaments on the bone, combined with the impact of walking and standing, triggers your body to deposit calcium at the point of strain. The result is a bony growth on the underside (or back) of the heel bone that can range from a few millimeters to over a centimeter in length. Interestingly, 15 to 25 percent of people with heel spurs have no pain at all, which tells us a lot about what’s really going on beneath the surface.
How a Heel Spur Actually Forms
Your heel bone absorbs the majority of your body weight with every step. When the tissues attached to it, particularly the thick band of connective tissue running along the sole of your foot, are repeatedly strained, microdamage accumulates at the point where they connect to the bone. A single injury won’t do it. Studies show that a one-time trauma is not enough to start spur formation, but repeated low-force impacts cause gradual changes in the bone tissue. As the impact force increases, fewer repetitions are needed to trigger those changes.
Your body responds to this ongoing stress the same way bone responds to any mechanical load: it builds more bone. This follows a well-established principle in biology where bone adapts its structure based on the forces placed on it. The spur grows in the direction of the stress, and its internal structure reflects this. Microscopic analysis reveals that the bony core of a spur is made of mature, layered bone with a cap of cartilage-like tissue on the surface, similar to what you’d find in a weight-bearing joint. That cartilage layer acts as a buffer, absorbing force and protecting surrounding tissue.
In other words, a heel spur isn’t a random calcium deposit. It’s your body’s attempt to reinforce a weak point, either to protect the heel bone from tiny fractures or to shore up the spot where the connective tissue anchors to the bone.
The Plantar Fasciitis Connection
Heel spurs and plantar fasciitis are closely linked, but they’re not the same thing. Plantar fasciitis is inflammation of the thick band of tissue on the bottom of your foot. That inflammation puts chronic tension on the heel bone, which can eventually lead to spur formation. In one study of 109 patients with plantar fasciitis, about 76 percent had a visible heel spur on X-ray. The spurs came in different shapes: most grew horizontally along the sole of the foot, while others pointed downward or curved into a hook shape.
Here’s what surprises most people: neither the shape nor the size of the spur correlated with how much pain patients felt before treatment. This is consistent with the broader finding that many people walk around with heel spurs and never know it. The pain you feel with a heel spur is more often caused by the soft tissue inflammation around it than by the bony growth itself. The spur is a sign that something has been stressing your heel for a long time, but it’s rarely the direct source of the ache.
Excess Body Weight
Carrying extra weight is one of the strongest risk factors. Every pound you carry multiplies the ground-reaction force on your heel with each step. A study comparing patients with painful heel spurs to a control group found that average BMI was 35.2 in the spur group versus 30.9 in the control group. When researchers ran the numbers, people with a BMI over 30 had roughly 2.7 times the odds of developing a painful heel spur compared to those at a lower weight. That elevated risk was statistically significant across every weight category tested: overweight, obese, and severely obese.
Foot Mechanics and Gait Problems
How your foot moves when you walk or run matters as much as how much you weigh. Overpronation, where your foot rolls inward too far with each step, is a common mechanical trigger. It causes the arches of your feet to flatten beyond their normal range, stretching the connective tissue along the sole and placing extra strain on the muscles and tendons that support the arch. People who already have flat feet are especially prone to overpronation, which sets up a chain reaction: flattened arch, overstretched tissue, chronic tension at the heel bone, and eventually spur formation.
High arches create problems from the opposite direction. A rigid, high-arched foot doesn’t absorb shock well, concentrating impact forces on the heel and ball of the foot rather than distributing them across the sole. Either extreme, too flat or too rigid, increases the mechanical stress that drives spur development.
Footwear and Activity Patterns
Shoes that lack arch support or shock absorption force your foot’s soft tissues to do all the work of cushioning impact. Flip-flops, worn-out athletic shoes, and dress shoes with thin soles are common culprits. Running or jogging on hard surfaces like concrete compounds the problem, since the ground gives back nearly all the force your foot puts into it.
Choosing the right shoe for each activity makes a real difference. A walking shoe doesn’t provide the same heel cushioning or support pattern as a running shoe, and using one for the other increases the repetitive strain on your heel. Shoes with shock-absorbent soles and firm arch support reduce the microtrauma that accumulates over time.
Age and Gender
Heel spurs become dramatically more common as you get older. The incidence of plantar heel spurs (on the bottom of the heel) rises steadily with each decade, reaching 41.8 percent in people over 70. This makes sense: decades of walking means decades of cumulative stress on the heel bone, and the connective tissues gradually lose elasticity with age, making them less capable of absorbing force.
For spurs on the bottom of the heel, men and women develop them at roughly equal rates. But spurs on the back of the heel, near the Achilles tendon attachment, are significantly more common in women. This may relate to differences in footwear patterns, since shoes with rigid heel counters or elevated heels alter the tension on the back of the heel bone over time.
Other Contributing Factors
Several additional factors raise your risk:
- Prolonged standing: Jobs that keep you on your feet for hours, especially on hard floors, generate the kind of sustained, repetitive force that drives spur formation.
- Sudden increases in activity: Starting a new exercise routine or rapidly increasing running mileage can overwhelm tissues that haven’t adapted to the load.
- Tight calf muscles: When your calf muscles are chronically tight, they pull on the Achilles tendon, which in turn increases tension on the heel bone from behind. This is a common factor in posterior heel spurs.
Why the Spur Itself Often Isn’t the Problem
Up to 63 percent of people without any heel pain have been found to have calcaneal spurs on X-ray. This is one of the most important things to understand about heel spurs: finding one on an X-ray doesn’t necessarily explain your pain. In clinical studies, spurs larger than about 5.3 millimeters were associated with higher odds of symptoms, but many large spurs remain completely painless. The pain typically comes from the inflamed, overstressed soft tissue surrounding the spur, not from the bone growth pressing into your foot.
This distinction matters because it shifts the focus from the spur to what caused it. Addressing the underlying strain, through better footwear, weight management, stretching, or correcting abnormal foot mechanics, targets the actual source of pain rather than the body’s bony response to it.