Blisters are an unfortunate reality of ultramarathons. Whether it’s 50km or 350km, long-distance running makes blisters almost certain.
Foot care becomes another discipline within the sport, and you quickly get used to talking about, showing, and getting acquainted with feet.
In an ultramarathon, a hot spot can become race-defining. Thousands of foot strikes, prolonged exposure to moisture, terrain changes and swelling can quickly turn a minor irritation into a painful blister or, in some cases, an open wound. In multi-day events, limited recovery time and the need to run on already damaged feet compound the problem.
Blister prevention is not just about choosing the right socks at the start of the race and leaving it; it’s about ongoing foot care and managing the changing relationship between your skin, sock, and shoe over hours of use.
Ultramarathons: The perfect storm for blisters
Friction blisters develop when repeated shear forces damage the skin’s deeper layers. During running, the foot is repeatedly loaded while the skin and underlying tissues move relative to one another. Over time, this can cause skin layers to separate and fluid to accumulate. This forms a blister.
Ultramarathons can intensify the exposure to blisters in several ways:
- Repetition over distance: thousands of foot strikes create cumulative mechanical stress. A minor fit problem that is tolerable on a short run may become significant over several hours.
- Sweat and moisture: prolonged sweating can change skin properties and increase the difficulty of maintaining a comfortable skin–sock interface.
- Foot swelling: feet can change volume during prolonged exercise, altering pressure and the fit of footwear.
- Terrain variation: climbs, descents, cambered paths and technical trails change loading patterns and can increase toe movement or heel slippage.
- Changing conditions: rain, stream crossings, mud, grit and temperature changes can alter the environment inside the shoe.
- Fatigue: tired runners may be less attentive to early discomfort and more reluctant to stop and address a hot spot.
These factors intersect rather than operate independently. A shoe that fits comfortably at the start may become restrictive later as the foot swells; meanwhile, socks can concentrate stress in one area, leading to a blister.
Sock Construction and Why It Matters
Socks form the interface between the foot and the shoe. They cushion the skin, manage moisture, and reduce irritating movement or pressure points. However, not all sock designs have the same evidence behind them. For ultrarunners, sock selection involves more than choosing a fabric labelled moisture-wicking. Construction, thickness, cushioning, fit and the interaction with the shoe all matter.
Dense padded acrylic socks: provide cushioning and absorption of some mechanical stress
Double-layer socks: allow movement between the sock layers rather than the sock against the skin
Moisture-wicking synthetic or wool blends: help manage sweat and improve comfort
Seamless or toe socks: may reduce local irritation, bunching and pressure points
Sock thickness, cushioning density, fit, seam placement and the shape of the heel pocket all influence comfort. A sock that bunches or slips can create new friction points, even if its fabric is technically advanced.
A field study involving 37 military recruits compared polypropylene socks with a merino wool and synthetic blend. The blended socks were rated cooler, less damp and more comfortable, and two of the three measured skin sites were drier. However, the study measured physiological conditions and comfort rather than establishing that the blend prevents more blisters.
Look for socks that fit securely, stay smooth against the skin and offer appropriate cushioning. Treat marketing claims about specific fibres, seams or double-layer construction with caution unless they are supported by relevant clinical trials.
Does the shoe fit?
For ultrarunners, shoe fit is a moving target. Footwear that feels perfect during a 10 km training run may behave differently after eight hours on a rocky trail, especially if feet swell, socks get damp, or your gait changes with fatigue.
What you should look out for when choosing your shoe:
- Adequate toe-box space: toes need room to spread and move without repeatedly striking the front or sides of the shoe, especially on descents.
- A secure heel: excessive heel movement can contribute to irritation, but overtightening the laces can introduce new pressure points.
- Suitable volume: a shoe must accommodate the runner’s intended sock thickness and changes in foot volume without becoming loose or restrictive.
- Appropriate lacing: adjusting laces can help manage heel hold and pressure across the instep. Test any changes during training.
- Intact internal materials: worn linings, compressed insoles and rough seams may create localised stress.
- Debris protection: trail gaiters can help prevent sand, grit and small stones entering the shoe, especially on dusty or sandy courses.
So if I’m accounting for swelling, should I size up? Not automatically. While a larger shoe may provide useful room for some runners, too much volume can let the foot move more than intended, causing friction and blisters.
The right fit depends on foot shape, shoe construction, terrain, sock choice, and how the individual runner responds during prolonged exercise. It’s obvious advice but you should not be running on race day with brand new shoes. Test your intended race shoes, socks and lacing during your long runs. A shoe that feels comfortable standing still has not necessarily passed an ultramarathon-specific fit test.
Should I lube up?
Anti-friction creams and balms are common within ultramarathons. Petroleum jelly and silicone-based products reduce surface friction around hot spots like the toes and heel.
Some favourites:
Body Glide Outdoor Anti-Chafe Balm
Squirrels Nut Butter Anti-Blister and Skin Repair
While popular, lubricants on their own cannot 100% prevent blisters. To prepare for your race, layer several protective measures to help prevent blisters. Layer your feet with a lubricant, choose the right socks and footwear, and reassess your feet throughout the race to prevent hot spots from becoming full-blown blisters.
Some runners suggest using talcum powder instead of lubricants to help absorb moisture and reduce friction. Depending on your needs and the race specifications, this can also be a good option.
Let’s tape it up and hope for the best?
For ultrarunners, dressings can be both a preventative tool and a way to protect damaged skin if a blister forms.
Hydrocolloid dressings: These moist dressings protect the affected area, can reduce pain and support healing. The NHS recommends them for existing blisters. Their ability to prevent a blister from forming in the first place is less firmly established.
Foam or felt padding: A ring-shaped pad can redistribute pressure around an existing blister, helping to keep direct pressure off the damaged area. Careful placement matters: bulky or poorly secured padding may create additional rubbing.
Adhesive tape: Taping your toes can reduce friction between toes or add another layer of protection for your toenails, especially if you have previously damaged nailbeds. However, if you don’t tape correctly, the tape can change how your foot moves, which can increase your chances of getting blisters.
Foot care is a full race discipline
A practical race-day routine could look like this:
Notice the warning signs
Burning, tenderness, unusual warmth, or a rubbing sensation can indicate a developing hot spot. Do not wait for visible skin damage.
Inspect the foot and shoe
Look for redness, damp or wrinkled socks, grit, a shifted insole, loose laces or a pressure point.
Correct the cause
Remove debris, smooth the sock, adjust lacing or replace wet socks where appropriate. Protect a vulnerable area with a suitable dressing or padding if needed.
Reassess before continuing
Check that the intervention lies flat and does not create a new pressure point. If pain persists or worsens, seek medical support rather than simply running through it.
This routine is practical advice based on established podiatry guidance, not a race protocol validated by a controlled clinical trial. On courses with sand, grit or loose debris, gaiters may help prevent foreign material entering the shoe. They are particularly relevant to trail races, but they cannot prevent blisters caused by pressure or internal shear.
Why no single product prevents every blister
The research suggests blister prevention depends on interacting forces, not a simple contest between competing brands.
A blister forms through repeated shear deformation within the skin. The 2024 critical review identifies three key elements: movement of the underlying bone, frictional forces at the skin–footwear interface and repetition of the resulting stress. Preventive strategies can therefore target different parts of the process, but no single intervention necessarily addresses all three.
For example:
A cushioned sock may help absorb some mechanical stress but cannot correct a shoe that allows excessive movement.
A lubricant may alter surface friction but cannot guarantee that the underlying tissues will stop moving relative to the skin.
Tape may protect a selected area but can loosen, crease or fail to address a different pressure point.
The practical lesson is to develop an individualised system through training, monitor the feet during the event and address early symptoms before they escalate.
Race Day Foot Care Plan
Before the race
- Test race shoes and socks on long runs and technical descents.
- Identify recurring hot spots and trial any tape, balm or padding.
- Check shoe linings, insoles, laces and toe-box space.
- Prepare spare socks, dressings and a small foot-care kit.
During the race
- Respond promptly to burning, tenderness or rubbing.
- Remove grit and check for sock folds or shifted insoles.
- Change wet or uncomfortable socks when useful.
- Inspect and reassess any taped or padded area.
After the race
- Clean and inspect the feet for blisters, broken skin or swelling.
- Protect damaged skin and avoid deliberately bursting blisters.
- Seek medical advice for infection signs, severe pain or worsening wounds.
These are practical recommendations based on podiatry guidance and the available research, not a validated clinical protocol. Runners with diabetes, reduced sensation, or circulation problems should seek individual medical advice about foot wounds pre-race.
Specialist socks, careful shoe selection, lubricants, tape and dressings all have potential roles, but the evidence is uneven. Test equipment during training, learn where and when hot spots develop, inspect the feet during the race and intervene early. For ultrarunners, the best blister strategy isn’t a miracle product: it is a well-tested, adaptable foot care system that evolves with the event’s demands.
Citations:
Prevention of Friction Blisters in Outdoor Pursuits: A Systematic Review (2017)
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