Blister Prevention for Ultramarathons

Why Blisters Happen

Friction blisters form when repeated rubbing separates cells in the upper layer of the skin and fluid fills the gap. The harder the rubbing, the fewer cycles it takes. Damp skin grips harder than very dry or soaking-wet skin, and heavier loads and harder effort both raise the risk (Knapik 1995). An ultra multiplies the number of cycles, and sweat, rain, grit, and heat keep changing the foot-shoe interface for hours.

How Often Ultrarunners Blister

In a stage race or multiday event, plan as if you will blister, and plan for it early: most blisters in the 128-runner trial were in place by the end of the second day. Your own history is the strongest predictor. Tape the spots that blistered last time. In the Al Andalus study, more ultramarathon experience was linked to fewer blisters in men.

Layered Risk Reduction

Socks and Gaiters

The evidence on socks is thin and mostly negative. In the Al Andalus stage race, the type and fabric of runners' socks made no difference to blister rates (Scheer 2014). A systematic review of 11 prevention trials found little high-quality support for any sock (Worthing 2017). Two older findings are the exception. A thin polyester sock worn under a thick wool or polypropylene sock reduced blisters in Marine recruits, and acrylic socks led to fewer blisters in runners (Knapik 1995).

What to Wear

• Default: a smooth synthetic or merino-blend running sock with flat toe seams that you have worn on your longest training runs.
• Blisters on or between the toes: try toe socks. No trial has tested them, but a 2016 review counts toe and double-layer socks among methods with a sound mechanism that still need research (Hoffman 2016).
• Heel or ball-of-foot blisters despite tape: try a thin polyester liner under a thicker wool or polypropylene sock, the only combination with trial support.
• Sand and desert stages: wear single-layer socks. Sand builds up between the layers of double socks (RacingThePlanet guide).
• Gaiters: wear them on sand, scree, and dusty trails. No trial has tested gaiters, but keeping grit away from the skin is one of the key strategies in a 2016 review (Hoffman 2016), and a gaiter is the simplest way to do it. This is our recommendation.

When to Change Socks

Plan one dry pair every 4 hours. That is six pairs for 24 hours on a crewed loop in dry weather, the planning number in our foot-care kit. Change sooner when a pair is wet, gritty, or wrinkled, and look at your feet every time. Wetness matters: among 315 hikers on the Camino de Santiago, 74% had blisters, and wet socks at the end of the day were an independent risk factor (Chicharro-Luna 2020).

Taping Methods

Paper tape is the one prevention method with randomized-trial support in ultrarunners. In the Pre-TAPED II trial, medical staff applied 3M Micropore paper tape before the start to one randomly chosen foot of 128 runners in four 250 km six-stage desert races. The tape went on each runner's blister-prone areas, and untaped skin on the same foot served as the control. Tape cut blister incidence by 40 percentage points (95% CI 28–52). Among the 109 runners who kept the protocol, 26% blistered under the tape and 68% on untaped skin of the same foot (Lipman 2016).

Two results temper that. The same group's first trial compared a taped foot with the runner's untaped other foot and found no protective effect (52% versus 39% blistered, P = 0.22; Lipman 2014). In the Al Andalus study, runners who taped prophylactically did not blister less (Scheer 2014), although that study was observational and did not control tape type or technique. A systematic review still rates paper tape as the only barrier with moderate confidence in its effect (Worthing 2017). Our verdict: tape your known hot spots.

How to Tape: The Trial Method

1. Use 1-inch (2.5 cm) and 2-inch (5.1 cm) paper tape, such as 3M Micropore. Clean and dry the skin first, and keep lubricant off any skin you are taping.
2. Toes: lay a 1-inch strip along the toe from the tip, then wrap a second 1-inch strip around it, snug but not tight. Do not tape between the toes, where tape edges rub (RacingThePlanet guide).
3. Heel or ball of the foot: lay one 2-inch strip across the heel or across the metatarsal head behind the toe.
4. Round the corners and smooth out every wrinkle.
5. Check the tape at every sock change and at the end of every stage, and replace any strip that has lifted. Lost adhesion was the most common reason runners could not follow the trial protocol (10 of 19).
6. Rehearse the full application on long training runs, and remove the tape slowly. Stop if it irritates the skin or constricts a toe.

Low-Friction Patches

PTFE patches, such as ENGO, stick to the inside of the shoe or insole rather than to the skin and lower friction where the shoe rubs. There is no trial in runners. The 2016 review lists low-friction patches among methods with theoretical support that still need research (Hoffman 2016). Try one if a heel spot keeps blistering through tape, and check that its edge does not create a new ridge.

Lubricant, Powder and Antiperspirant

In the Al Andalus stage race, neither lubricant, talcum powder, nor antiperspirant reduced blister rates (Scheer 2014). An older review reached the same conclusion for antiperspirants with emollients and for drying powders (Knapik 1995). Lubricant is still the most popular measure: 79% of French trail ultrarunners who used any prevention used an anti-friction cream (Damoisy 2023).

Our verdict on lubricant: optional. Use it only if it has worked on your longest training runs, never for the first time on race day. Keep it off skin you plan to tape, because it stops tape from sticking.

One controlled trial did find an antiperspirant effect, at a cost. West Point cadets applied 20% aluminum chloride hexahydrate in alcohol to their feet for up to five nights before a 21 km hike. Among cadets who used it on at least three nights, 21% blistered against 48% on placebo, but 57% reported skin irritation against 6% (Knapik 1998).

Our verdict on antiperspirant: worth testing only if your feet sweat heavily and you blister despite tape. Try it for three to five nights before a long training run, not in race week, and stop if the skin cracks or itches.

Shoe Fit for Long Events

Do not size up by default. In 76 runners measured before and after a 100 km race, average foot volume did not change. The runners whose feet swelled were the ones who drank more (r = 0.54; Cejka 2012). A bigger shoe that lets the foot slide adds shear rather than removing it.

• Race in the model and size of your longest training runs, with about a thumb's width in front of the longest toe, the usual fitting rule.
• Fix heel slip with lacing, such as a heel-lock loop, before changing size.
• If your feet visibly swell during a race, check your drinking against thirst before you change shoes. The hydration and sodium guide covers how much to drink.
• Pack a half-size-larger or wider pair only if your feet swelled in a previous multiday event and you have trained in that pair. No study has measured foot volume over 48 hours or six days, so this is our recommendation.

For staging pairs across a long race, see the shoe rotation strategy and the best shoes for 24-hour races.

Calluses and Toenails

Thick calluses raise the stakes. A blister that forms under a callus is deep, hard to drain, and can end a race (RacingThePlanet guide), and callus removal is one of the key prevention strategies in Hoffman's 2016 review.

• File calluses down with a foot file in the weeks before the race and moisturize afterward, so the skin is thin and supple rather than hard.
• Trim toenails straight across and file the corners smooth two to three days before the start. A nicked edge then has time to settle, and a long nail will not hit the shoe on descents.
• A black or painful toenail usually means the toe is hitting the front of the shoe. Fix the fit and lacing rather than taping harder.

Mid-Race Blister Management

Race medical or foot-care staff are the first choice when they are there, because they treat feet all day. When you or your crew have to do it, use this table.

How to Drain a Blister

1. Clean your hands, then clean the blister with an alcohol wipe or soap and water.
2. Puncture the blister at its edge, close to healthy skin, with a sterile needle or lancet. One or two small holes are enough.
3. Press the fluid out gently with clean gauze.
4. Leave the roof in place. Draining while keeping the roof gives the least discomfort and may lower the risk of infection (Knapik 1995).
5. Cover it with a hydrocolloid dressing, or with a non-stick pad held by paper tape, and smooth every edge.
6. Recheck it at the next stop, and drain it again if it refills.

This is the method in Knapik's review and in RacingThePlanet's guide written with race physicians Brian Krabak and Louis Davenport, which limits drainage to large, painful blisters that are not bloody. The Wilderness Medical Society's field wound guideline covers cleaning and dressing open wounds (Quinn 2014). The supplies are listed in the foot-care kit for multiday running.

Prevention Checklist

Race morning:

• ☐ Wash and fully dry feet
• ☐ Tape known hot spots with paper tape, using the method you rehearsed
• ☐ Apply lubricant only if it worked in training, and keep it off taped skin
• ☐ Put on the race socks and gaiters you tested
• ☐ Lace with the pattern that held your heel without pressure in training

At every sock change (every 4 hours on a crewed loop, or sooner if wet, gritty, or wrinkled):

• ☐ Remove shoes and socks, and look at every toe, the heel, and the ball of the foot
• ☐ Dry feet, and shake grit out of shoes and gaiters
• ☐ Replace any lifted tape
• ☐ Treat any blister using the table above
• ☐ Put on a fresh, dry pair

For what to pack and how much, use the foot-care kit for multiday running. For a self-supported stage race, add it to the stage race packing list.