Foot Care, Blisters, and Chafing

How blisters form and who gets them

A 2024 expert paper argues that foot friction blisters are caused by repetitive shear deformation, with three elements: motion of the bone, a high friction force and repetition of the resulting shear events. It says rubbing at the skin surface is not the mechanism².

Blisters come early and pile up. In a 2014 study of 50 runners in a 5-day, 219 km (136 mile) stage race, 34% had blisters after day 1 and 76% after day 4, and most were on the toes (65%)¹. In a survey of 533 French trail ultramarathon runners published in 2023, 29% had blisters at the finish, and runners who had blistered before were far more likely to blister again. The authors wrote that none of the prevention methods studied seemed to match the protective effect of running shorter distances³. If you have blistered before, expect it again and prepare for it, and do not make a race the first time your feet cover that distance.

In the weeks before

A 2024 critical assessment of blister prevention found the best support for strategies that build the skin's resilience to shear gradually and for breaking in footwear⁴:

• Raise your load gradually and get your feet used to the activity and the terrain. Blisters cluster early in a program: in one cohort of military cadets, 42.1% blistered, with 95% of the cases in the first 3 weeks⁴.
• Wear your race shoes on your long runs. Among 2,617 military cadets, those who wore their boots more than 20 hours a week in the 2 weeks before training had fewer blisters (29.7% against 44.4%)⁴.
• Do not build thick callus. The same paper calls excessive callus counterproductive, because a thick callus is a known risk factor for friction blisters⁴.

What to wear, and what to skip

The same 2024 assessment sorts what runners put on their feet by the evidence behind it⁴:

• Socks. Choose dense, padded acrylic socks, and avoid creases. In 35 long-distance runners, cotton socks had twice as many blisters, three times as large, as acrylic. In a follow-up with less padding, the two fibers did not differ, so the padding matters more than the fiber on the label.
• Insoles. Neoprene insoles had supporting evidence: in 90 Coast Guard recruits, blisters and calluses occurred in 8 of 30 controls and 1 of 30 wearing neoprene insoles.
• Powder and antiperspirant. Skip both. Powder either had no effect or raised the chance of blisters. Antiperspirants that reduced blisters in military trials also caused significant irritant dermatitis, and non-irritating ones did not prevent blisters.
• Lubricant, toe socks, double socks and tape. Unproven. Results for paper tape and double-sock systems are mixed, and lubricants and toe socks lack clinical evidence. Some ultra coaches still teach taping a known problem spot, for example with kinesiology tape and tincture of benzoin, so try any of these on long runs before race day, one at a time.
• Tape allergy. In a 2023 study of 26 conscripts who wore medical adhesive tape for several days, 20 (77%) had contact allergy to the tapes, and the authors concluded that prolonged use of medical adhesive tape on intact skin carries a high risk of allergic contact dermatitis⁵.
• Grit and worn gear. Gaiters keep debris out of your shoes. Inspect socks, insoles and shoe linings regularly for compaction and wear, because worn materials absorb less shear.

Chafing

In a 2014 study of 76 road runners in southern Brazil, 42.1% reported chafing, and jogger's nipple was more frequent in those running more than 64 km (40 miles) a week⁶. Find your rub points before race day: run your longest run in the exact clothes, and the loaded hydration vest, you will race in, and fix the spots that rub. In laboratory tests on skin, petrolatum, mineral oil and glycerin reduced friction for about 90 minutes, and by 3 hours friction was 35% above baseline, so on a long run plan to reapply⁴.

On the run

Deal with a hot spot when you first feel it, and keep dealing with small problems early and often. Late in a 100-mile race, with your feet already wrecked and the finish close, a ten-minute fix may not be worth it. If you have a crew, put one person in charge of your feet. A shoe and sock combination that worked in training can stop working partway through a hot, wet race, and in a 2022 study of 203 hikers, hiking in wet socks went with about twice the risk of foot blisters, an observational finding⁷. Have a dry pair ready.

Your feet change over a long run. A 2018 study scanned 26 recreational runners after 10 and 20 km (6 and 12 miles) on a track and found significant changes in ball width, arch height and foot volume⁸. Check how your race shoes feel at the end of your longest run, not the start. The guide on running shoes covers fit.

Treating a blister

A 1995 review says clinical experience suggests that draining an intact blister while keeping the blister roof results in the least discomfort and may lower the chance of secondary infection, that hydrocolloid dressings on deroofed blisters give pain relief, and that there is no evidence antibiotics influence blister healing⁹. A 2024 paper notes that blister dressings differ in friction but cites no clinical outcome data for any of them⁴. If the same spot blisters every time, ask a clinician to look at the cause, such as a toe deformity or your gait, because covering the spot treats only the symptom; that approach is unproven⁴.