A blister is the skin's response to repeated shearing. The upper layer slides against the layer beneath, they separate, and fluid fills the gap to cushion the damage. Two ingredients are required: friction and moisture. Take away either and most blisters never form.
Deal with the moisture
Damp skin is softer, grips more, and shears more readily. This is why blisters cluster in hot weather and on long days.
Dust cornstarch over completely dry feet in the morning and shake a teaspoon into each sock. It absorbs sweat and lets sock and skin slide rather than drag. Reapply at midday if you are on your feet.
Wear socks that move moisture — wool or synthetic. Cotton holds sweat against the skin and is the worst choice for long days, despite its reputation.
Deal with the friction
- Shoes that fit. Too big lets the foot slide; too small presses. Both blister.
- Break new shoes in gradually — an hour at a time, not a full day.
- Lace properly. A heel lock stops the foot sliding forward on descents.
- Seamless socks, and never two pairs of thin cotton.
- Tape the spots you know blister before you set out, not after.
Listen for the hot spot
Almost every blister announces itself first as a warm, tender patch. That is the moment to stop — not in twenty minutes, not at the next break. Take the shoe off, dry the foot, and cover the spot with tape or a dressing.
Two minutes there saves a week of limping.
If one forms
Leave it intact if you can. The roof is a sterile dressing and nothing you buy is better. Pad around it with a doughnut of felt so the pressure lands on the ring rather than the blister.
If it is large, painful and certain to burst anyway, drain it cleanly: sterilise a needle, pierce the edge low down, press the fluid out gently, and leave the roof in place. Dress it and keep it clean.
Two drops of eucalyptus in a teaspoon of carrier oil, dabbed around — not on — an intact blister keeps the area clean. Once broken, treat it as a wound: clean, dry, covered.
Never do this with diabetes
Do not drain a blister yourself if you have diabetes or poor circulation. What is a minor nuisance on a healthy foot is a route to a serious infection on a neuropathic one. Call your podiatrist instead — see diabetic foot care.
More on blisters and cornstarch.
Taping before you go
If you already know where you blister — most people do, and it is usually the same two or three spots — pre-taping is the single most effective thing on this page. It prevents rather than treats.
Use zinc oxide tape or kinesiology tape rather than a plaster, which is designed to cushion a wound rather than reduce friction. Apply it to clean, completely dry skin before you set out. Round the corners of the tape so it does not catch and peel, and smooth it flat with no wrinkles — a wrinkle in the tape is itself a friction point and will raise a blister of its own.
For long days, some walkers use a thin liner sock under a thicker one, so the two socks slide against each other rather than the sock sliding against skin. It works well, provided the extra bulk does not make the shoe tight.
Carry tape with you. The hot spot you feel at mile four is trivial to deal with in the moment and miserable to deal with the following morning.