In ultramarathon running, your feet absorb tens of thousands of repetitive impacts across distances that can stretch well beyond 50 miles. Over that kind of sustained effort, even small friction patterns tend to compound into painful hot spots on feet that may progress into full blisters if left unaddressed. Understanding what causes these irritations, and knowing how to handle them both before and during a race, may be the difference between a strong finish and a painful slog through the final miles.
What Causes Hot Spots on Feet During Ultramarathons
Hot spots develop when repetitive shear forces act on the skin of your feet. A 2024 review published in the Journal of Athletic Training identified three key factors in friction blister formation: the number of shear cycles, the skin's natural resilience to shear deformation, and the magnitude of that deformation. In an ultramarathon, all three factors are amplified. Tens of thousands of stride cycles generate sustained friction, while moisture from sweat or weather conditions may soften the skin and reduce its ability to resist repetitive stress.
Foot swelling is another common contributor. As the miles accumulate, your feet tend to expand due to increased blood flow and fluid retention. Shoes that fit well at mile one can feel noticeably tighter by mile 40, increasing pressure points and creating new areas of friction. Heat buildup inside the shoe also plays a role, as elevated tissue temperature may accelerate the fatigue process in the outer layers of skin.
Preventing Hot Spots Before Race Day
Get the Right Footwear Fit
Your shoes should have enough room in the toe box to accommodate natural foot expansion over long distances while still holding the midfoot and heel securely. Many experienced ultrarunners size up a half to full size for race day to account for swelling. Test your race shoes on your longest training runs well in advance and pay attention to any emerging pressure points. Shoes that create even mild discomfort at 20 miles will likely cause significant problems at 60.
Build a Sock Strategy for Ultra Distance
The right socks play a critical role in managing friction and protecting your skin over extended distances. Look for a close anatomic fit that minimizes bunching and internal movement, as loose material tends to create friction zones where hot spots form. For runners seeking full calf-to-foot coverage with targeted support, women's tall compression socks are designed to provide a secure, anatomical fit that may help reduce slippage and friction during long efforts. Mid-cut compression socks offer a versatile option for those who prefer less coverage while still benefiting from a performance-driven fit. If you favor a lower profile, performance low-cut and no-show socks are built with comfort and blister-prevention features suited to warmer conditions and personal preference.
Carry spare pairs in your drop bags. Changing into a fresh, dry pair of socks at crew access points or aid stations may help reset your foot environment and reduce the moisture buildup that contributes to hot spots on feet.
Prepare Your Skin for Repeated Friction
In the weeks leading up to your race, keep your feet well-moisturized so the skin stays supple rather than dry and prone to cracking. Reduce any excessive callus buildup, since blisters that form beneath thick calluses tend to be painful and difficult to manage mid-race. On race morning, apply a thin layer of lubricant to common hot spot areas like the toes, heels, and ball of the foot. Some runners also use preventive taping on known trouble spots, though effectiveness may vary by individual.
Mid-Race Fixes When Hot Spots Appear
Catch Hot Spots Early
The single most important thing you can do during an ultra is respond to hot spots the moment you feel them. A hot spot is your body signaling that tissue damage is building beneath the surface. If you feel a warm, tender area developing on your foot, that is your window to intervene before the irritation progresses. Ignoring the sensation and pushing through rarely ends well over ultra distances.
Quick Fixes at Aid Stations
When you reach an aid station or crew point with a developing hot spot, take a few minutes to address it properly:
- Remove your shoes and socks. Inspect the affected area visually and let your feet air briefly.
- Clean the hot spot and the surrounding skin, then dry the area thoroughly.
- Apply lubricant or a protective barrier to the irritated zone.
- Use a thin, flexible tape over the hot spot, smoothing it carefully to avoid any wrinkles or folds that could create new friction points.
- Put on a fresh pair of dry socks if available.
This process adds only a few minutes to your stop and may save you from dealing with a far more painful blister later. Pack a small foot-care kit in each drop bag so supplies are always within reach.
How the Right Socks Help Protect Against Hot Spots on Feet
Not all socks perform the same way over ultra distances. The construction quality, fit precision, and material choice directly affect how much friction reaches your skin. Socks engineered with an anatomical fit are designed to move with your foot rather than against it, which may help reduce the sliding that leads to hot spots. Targeted cushioning in high-impact zones and a secure fit around the arch and heel are particularly valuable when covering 50, 100, or more miles in a single effort.
German-engineered brands rooted in performance science, like CEP, approach sock design with precision sizing based on calf and ankle circumference rather than standard shoe size. This attention to anatomical accuracy is designed to deliver a more individualized fit that may help minimize internal movement and reduce friction across your foot during prolonged activity.
Post-Ultra Foot Care and Recovery
After crossing the finish line, remove your shoes and socks promptly and let your feet air out. Clean any irritated areas gently and avoid popping intact blisters, as the overlying skin provides a natural barrier. Elevating your feet and wearing loose footwear in the hours after your race may help reduce swelling. If irritation persists or worsens over the following days, consider consulting a medical professional.
Foot care is not a secondary concern in ultramarathon running. It is a core part of race strategy. With the right preparation, smart sock choices, and a willingness to address hot spots before they escalate, you may keep your feet in race-ready condition from start to finish.
Frequently Asked Questions
What is a hot spot on the foot, and how is it different from a blister?
A hot spot is an early warning sign of friction damage. It typically presents as a warm, tender area on the skin that has not yet developed into a fluid-filled blister. Addressing hot spots promptly may help prevent them from progressing further.
How often should I change socks during an ultramarathon?
Many ultrarunners find that changing socks every 20 to 30 miles, or whenever feet become noticeably wet, tends to help reduce friction and moisture buildup. Packing spare pairs in your drop bags makes this easy to manage on race day.
Can lubricants alone prevent hot spots during an ultra?
Lubricants may help reduce surface friction in the early miles, but they tend to wear off or become less effective as moisture accumulates over longer distances. Combining lubrication with well-fitting socks, proper shoe fit, and preventive taping is generally a more reliable approach.
Why do hot spots tend to get worse later in an ultramarathon?
Prolonged running causes feet to swell, increases moisture from sweat, and raises tissue temperature inside the shoe. These factors combine to create more friction and greater skin vulnerability as the race progresses, which is why early intervention matters so much.
Should I pop a blister that forms during a race?
Small, painless blisters are generally best left intact, as the overlying skin provides natural protection. If a blister becomes large and painful enough to affect your gait, draining it carefully with a sterilized needle and covering it with clean tape may help, though consulting medical staff at an aid station is always a good idea.
