Heel spurs form when repeated stress on the heel bone triggers your body to deposit extra calcium at the point where soft tissue attaches to the bone. Over months or years, these calcium deposits build into a bony protrusion that can extend up to half an inch from the heel bone’s surface. About 32% of adults have a heel spur on the bottom of their heel, and most of them have no idea because the spur itself usually causes no pain at all.
The Step-by-Step Process Behind a Heel Spur
Your heel bone, called the calcaneus, is the largest bone in the foot and absorbs the initial impact every time you walk, run, or jump. A thick band of connective tissue called the plantar fascia stretches from the bottom of this bone forward to your toes, acting like a bowstring that supports the arch. Tendons from the calf also attach at the back of the heel. These attachment points are where spurs develop.
When the plantar fascia or Achilles tendon is pulled too hard or too often, it creates micro-tears at the spot where the tissue connects to bone. Your body responds to this damage with inflammation, and as part of the healing process, it lays down new calcium at the injured attachment site. Think of it as your body trying to reinforce a weak point. The problem is that this reinforcement accumulates. Each round of damage and repair adds another thin layer of calcium, and over many months, these layers harden into a visible bony projection. On X-ray, a plantar heel spur typically looks like a small hook or shelf extending forward from the bottom of the heel bone.
This process is not fast. Heel spurs are the end result of longstanding tension on the plantar fascia insertion, meaning they represent chronic, repeated strain rather than a single injury. That’s why they’re far more common in older adults. The highest incidence, around 42%, occurs in people over age 70 who have had decades of cumulative foot stress.
Two Types of Heel Spurs
Not all heel spurs form in the same place. The more common type, a plantar calcaneal spur, grows on the underside of the heel bone where the plantar fascia attaches. A posterior calcaneal spur forms at the back of the heel where the Achilles tendon connects. Both develop through the same calcium-deposit mechanism, but posterior spurs are less common, appearing in about 13% of adults compared to 32% for plantar spurs.
Posterior spurs tend to be more noticeable because the back of the heel is closer to the skin’s surface. You might feel a hard bump at the back of your heel, and shoes that press against it can cause irritation. Plantar spurs sit deeper within the foot’s soft tissue and are typically discovered only on X-ray.
What Actually Causes the Strain
The underlying question is what creates enough repeated stress to trigger this calcium buildup in the first place. Several factors work alone or in combination.
Excess body weight is one of the most significant. Extra weight increases the load on both the plantar fascia and the heel bone with every step. Over time, that added pressure causes micro-tears in the tissue, leading to inflammation and eventually spur formation. Weight gain can also flatten the arches of the foot, which redistributes force in ways that concentrate even more stress on the heel.
Foot structure plays a major role. Flat feet allow the plantar fascia to stretch more than it should with each step, pulling harder at its heel attachment. High arches create the opposite problem: the fascia is pulled taut, concentrating force at the same attachment point. Either extreme increases the strain that leads to calcium deposition.
Footwear matters more than most people realize. Shoes that fail to cushion the heel or support the arch force your plantar fascia and heel bone to absorb impact that proper cushioning would dissipate. Worn-out athletic shoes, thin-soled flats, and shoes with rigid heel counters all contribute.
High-impact activities like running, jumping sports, and prolonged standing on hard surfaces accelerate the process by increasing both the frequency and intensity of heel strikes. Jobs that keep you on your feet for hours on concrete floors carry particular risk.
Why the Spur Itself Usually Doesn’t Hurt
This is the part that surprises most people. The American Academy of Orthopaedic Surgeons states clearly that heel spurs do not cause plantar fasciitis pain. Most people who have bone spurs on their heels do not have heel pain. The sharp morning pain in your heel, the ache after standing all day: that comes from the inflamed, damaged plantar fascia, not from the bony growth.
This distinction matters because it changes how treatment works. Plantar fasciitis pain can be treated without removing the spur. Stretching the fascia, reducing inflammation, improving footwear, and offloading the heel with orthotics address the actual source of pain. Even when surgery is performed for severe plantar fasciitis, removing the spur is not usually done because the spur isn’t causing the problem.
The spur and the pain share a common cause (chronic strain) but exist somewhat independently of each other. You can have a large spur with no symptoms, or intense heel pain with no visible spur. The spur is essentially a marker of long-term stress rather than a source of injury.
How Long They Take to Develop
Heel spurs don’t appear overnight. The process of repeated micro-damage, inflammation, and calcium layering unfolds over many months to years. This is why spurs are strongly age-related. In studies of adults under 40, plantar spur incidence is relatively low. By the 60s, both plantar and posterior spur rates climb significantly, with posterior spurs peaking around 22% in people between 61 and 70. Women develop heel spurs at slightly higher rates than men (34% versus 31% for plantar spurs), which may relate to differences in footwear, bone density changes, and weight distribution.
Because the formation process is so gradual, there’s no single moment when a spur “forms.” It grows incrementally, and by the time it’s large enough to show up on an X-ray, the repetitive strain has likely been present for a long time. This also means that the same gradual process can sometimes be slowed or halted by addressing the underlying strain: improving footwear, losing weight, stretching the plantar fascia regularly, or correcting biomechanical issues with orthotics. The existing calcium deposit won’t dissolve, but you can reduce the stimulus that was building it up.