Pain on the side of your heel usually comes from one of a handful of conditions involving tendons, nerves, or the connective tissue that runs along the bottom of your foot. Which one you’re dealing with depends on whether the pain is on the inner or outer side, whether it burns or aches, and what makes it worse. Here’s how to narrow it down.
Outer Heel Pain: Peroneal Tendonitis
The most common reason for pain on the outside of your heel is irritation of the peroneal tendons, which run along your outer ankle bone and down the side of your foot toward your little toe. When these tendons get overworked or inflamed, you’ll feel an aching pain along the outer edge of your heel and ankle that gets worse with activity and improves with rest. You may also notice swelling, warmth, or a thickened area along the tendon that you can feel when you press on it.
Peroneal tendonitis typically develops from repetitive overuse, like increasing your running mileage too quickly or spending long hours on your feet. It can also follow an acute ankle sprain. The pain tends to build gradually rather than appearing out of nowhere, and it’s usually worst during or right after physical activity. Treatment starts with reducing the activity that’s causing problems, icing the area, and doing eccentric exercises (slow, controlled movements that lengthen the tendon under load). Most people improve with these steps over several weeks.
Outer Heel Pain: Sinus Tarsi Syndrome
If your outer heel pain comes with a feeling that your foot or ankle is unstable, especially on uneven ground, sinus tarsi syndrome may be the culprit. The sinus tarsi is a small channel on the outside of the foot between the ankle bone and the heel bone. When the ligaments and tissues in this space become inflamed, typically after repeated ankle sprains, you get pain along the outer heel and ankle that worsens with exercise or walking on uneven surfaces.
This condition is treated with orthotics, ice, anti-inflammatory medication, physical therapy focused on balance and strengthening, and occasionally corticosteroid injections. The key differentiator from peroneal tendonitis is that instability feeling. If you’ve had multiple ankle sprains and your outer heel aches, this is worth considering.
Inner Heel Pain: Tarsal Tunnel Syndrome
Pain on the inside of your heel, especially if it’s accompanied by burning, tingling, or numbness, often points to tarsal tunnel syndrome. This happens when the posterior tibial nerve gets compressed as it passes through a narrow space behind the inner ankle bone. The resulting pain and numbness can spread from the inner heel down into the sole and toes.
Walking, standing, and running typically make it worse. The nerve-related quality of the pain is what sets this apart from tendon problems. If your heel pain feels more like an electrical or burning sensation than a deep ache, nerve compression is a likely explanation. A related condition, Baxter’s neuropathy, involves compression of a smaller nerve branch and can cause sharp, shooting pain that radiates across the foot. It’s commonly misdiagnosed as plantar fasciitis, but the giveaway is sensory changes like numbness or tingling on the bottom of the foot, which plantar fasciitis doesn’t cause.
Lateral Plantar Fascia Pain
Most people associate plantar fasciitis with the bottom of the heel, but the plantar fascia has a lateral cord that runs along the outer edge of the foot. When this lateral cord becomes inflamed, it produces pain on the outer side of the heel and foot, near the base of the fifth metatarsal (the bony bump on the outside of your midfoot).
The telltale sign is pain that’s worse after rest, particularly those first steps in the morning or after sitting for a long time. You may also notice tenderness and mild swelling when you press along the outer edge of the foot near that bony bump. This pattern of “worse after rest, better with movement, then worse again with prolonged activity” is characteristic of fascia problems rather than nerve or tendon issues. Most people with plantar fascia problems recover within several months using conservative approaches: icing, stretching, arch supports to distribute pressure more evenly, and temporarily avoiding activities that aggravate the pain.
Heel Fat Pad Syndrome
Your heel has a built-in shock absorber: a fat pad made of fatty tissue and thick elastic fibers, normally 1 to 2 centimeters thick. Over time, this padding can thin out or lose its elasticity, leaving the heel bone less protected. The result is a deep, bruise-like pain in the heel that can radiate to the sides.
You can test for this by pressing firmly into the center of your heel. If that reproduces the pain, fat pad thinning is a possibility. The pain is typically worst when walking barefoot on hard surfaces like tile or concrete, during high-impact activities like jumping or running, and after long periods of standing. Unlike plantar fasciitis, this pain doesn’t follow the classic “worst first thing in the morning” pattern. It’s more directly tied to impact and pressure. Cushioned insoles and supportive footwear are the first line of management.
Calcaneal Stress Fracture
A stress fracture of the heel bone (calcaneus) can produce pain on either side of the heel, and it’s the diagnosis you don’t want to miss. This is most common in runners, military recruits, and others who suddenly ramp up high-impact activity. The pain is usually diffuse rather than pinpointed, and it tends to get steadily worse with continued activity rather than coming and going.
A simple screening test involves squeezing both sides of the heel with your hands. If this squeeze produces pain, a stress fracture is possible, though imaging is needed to confirm. The squeeze test is highly specific (meaning a positive result is a strong signal) but not very sensitive (a negative result doesn’t rule it out). If your side-of-heel pain started after a jump in training volume and isn’t improving with rest, this is worth getting evaluated.
How to Tell What You’re Dealing With
The quality of the pain is your best clue. A deep ache that worsens with activity and improves with rest points toward tendons or the fat pad. Burning, tingling, or numbness suggests nerve involvement. Pain that’s worst with your first morning steps and eases as you move is classic for fascia problems. Pain that steadily worsens over days or weeks with no improvement from rest raises the possibility of a stress fracture.
Location matters too. Outer heel pain with a history of ankle sprains suggests peroneal tendonitis or sinus tarsi syndrome. Inner heel pain with tingling points toward tarsal tunnel syndrome. Pain that you can reproduce by pressing the center of the heel suggests fat pad issues.
One pattern to watch for: heel pain on both feet accompanied by joint swelling, redness, or warmth elsewhere can signal a systemic inflammatory condition like psoriatic arthritis or ankylosing spondylitis rather than a mechanical problem. These conditions often cause pain at the point where tendons attach to bone, and the heel is a common site. If your heel pain showed up alongside stiffness in your lower back, swollen toes, or a skin rash, that’s a different evaluation entirely.