A blister is the direct result of a combination between friction and an excessively moist foot environment, causing separation between the epidermis and the dermis (layers of the skin). In response to this, fluid enters the site and increases pressure in the area, resulting in a blister. If blood vessels are damaged from the friction, this will develop into a blood blister, which is when it can get messy and potentially dangerous.

It is common for endurance runners to develop blisters over the course of a race; the reason for this is that in a race situation you often perspire more and are pouring gallons of water over your body. This fluid eventually flows down into your shoes, forming puddles around your toes; the associated friction from a higher pace may be sufficient to form blisters.

The very best way to prevent blisters is to stop after every 10km; shower, dry your feet and shoes, and put on a new pair of socks. Maybe not the most practical recommendation during a run, but there are alternatives:

Prevention of blisters for runners

It’s no use waiting for race day to see whether those new running shoes are going to cause blisters ...

• Be particular about what running shoes you should run in. There are many different brands, models and shapes in the market, but advice from an expert can steer you in the right direction. Avoid shoes that impinge on your toes from the sides and tops, as they are bound to cause some problems. Some shoes also have a higher ankle and heel counter, again a potential blister trap. Also shoes that have an extremely high instep can be a cause for blistering.

• Don’t be a slave to fashionable socks; if they have a sports label on them it doesn’t mean that they are what the athletes wear. Choose socks designed to wick moisture away from the foot (check in good running shoe shops). Avoid cotton ones, as these have a tendency to absorb moisture and, when dry, will turn into sandpaper.

• Try to keep your feet dry. However, don’t take a 10 minute detour around a puddle if everyone else is going straight through the middle.

• For races, put those week-old running shoes back in the closet until they have a decent amount of wear in them. Old favourites will probably be the better option.

• A regular foot inspection should identify any potential blister sites, as would general training runs.

• Regular application of a drying agent to the skin, such as methylated spirits, is a good option, especially to spots most at risk. Avoid doing this to an existing blister!

Treatment of blisters after a run

What you do once you have a blister depends largely on the size of the lesion, the mechanism of its development and who you talk to. Be aware that if the blister remains intact, and there is no fluid seeping out, then it is technically a sterile lesion and if possible it should remain intact. This is easy if the blister is not in a high weight bearing or stressed area and if the lesion is small.

If the blister is large and somewhere prominent, such as the heel or the side of the little toe, then it is not desirable to leave it intact. This is due to the amount of friction it would be exposed to and the pressure applied to it, especially if it is a large one.

In cases such as this, lance the side of the blister with a clean, preferably sterile needle and squeeze gently to remove the fluid. Make sure your hands are clean. Try to keep the roof of the blister intact, as this provides the best environment for healing.

An antiseptic dressing should be applied securely, so that it doesn’t shift once the foot is back in shoes. The dressing should be changed daily, more often if necessary. If the blister has already burst, then the same dressing principle should be adhered to. Extra care should be taken with blood blisters, as there is a greater risk of severe infection; look for pus and streaking.

Always be aware of the signs of inflammation:

• Redness
• Heat
• Swelling
• Pain

If at all concerned, contact your podiatrist or doctor about the blister.