Updated: Feb 15
Up to 50% of runners suffer from blisters at some stage. In this article, we’ll look at how blisters form, what causes blisters in runners, and how to prevent blisters. We’ll also answer questions like “Should I pop a blister?” and “Can I keep on running with a blister?” Remember, if you need more help with an injury, you're welcome to consult one of our physios online via video call.
When I looked at the research, it seemed that there’s much more money available for studies about soldiers getting blisters than for studies about runners getting blisters! Nevertheless, some of those findings are still useful for runners and obviously also for walkers.
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What happens when a blister forms?
Blisters form as the result of shearing forces within the skin caused by friction. Shearing force occurs when two forces act on something in parallel to each other but in different directions. An everyday example would be when you rub a fresh rubbish/garbage bag between your fingers to separate the layers clinging to each other.
The outer part of your skin is called the epidermis, and it is made up of four or five layers (depending on the type of skin).
The shearing forces caused by running or walking distort the skin cells in the epidermis. When this happens too frequently and/or with too much pressure, it damages the cells in the prickle layer of the epidermis, which connects the outer epidermal layers to the deeper down basal cell layer. The connection is destroyed and fluid then seeps into this split, separating the basal cell layer from the outer layers, with the latter forming the “roof” or “dome” of the blister.
Causes of blisters in runners
The blister-forming process described above can happen in two ways: from outside the skin (external friction) and from underneath the skin (internal friction).
Friction between the skin of the foot and the running sock (assuming that you do run with socks) is the main cause of blisters in runners. The amount of friction is influenced by the following factors.
Skin that is very dry or very wet experiences lower friction against the sock than skin that is moist. However, if the skin of your feet stay very wet for a long time while you’re running, it will become “pruny” and vulnerable to damage anyway.
The higher the pressure on your skin, the sooner a blister will form due to friction. Factors such as your weight, calluses, bunions, toenails that are not properly trimmed, poorly fitting shoes, and shoes that haven’t been broken in yet can all contribute to increased pressure on your skin in certain places, leading to blisters.
Foreign objects that get into your shoe can also cause trouble. The researchers call it “particulate matter” – as runners we know it as sand, mud, dust, or grass stubble. If some of this stuff gets between the skin and the sock or between the sock and shoe, it will increase the friction and can therefore cause blisters.
It is normal for the bones inside your foot to move while you’re running, but excessive movement can also cause blisters.
The type of running you do and the terrain that you run on can play a role here. The harder you push off with your feet, the more friction there will be between your bones and the soles of your feet. Also, running on steep inclines or downhills will cause more front-to-back friction, while running on a severe camber will cause more sideways friction.
A changed gait pattern due to inflexibility or weakness higher up in the body (e.g. weak glutes) can also increase the friction between your foot bones and your skin. For example, if you have tight calves, your foot arches may have to collapse somewhat when your feet hit the ground to compensate for it, which will increase the risk of internal friction in the plantar area of your foot.
A change in running style because you are tired can also contribute to blister-inducing internal friction.
The above mentioned effects of friction can be increased or decreased by certain skin characteristics.
If your feet are used to running, your skin would have adapted to deal with the usual amount of friction/shearing forces that it has to contend with and therefore you will be less at risk of getting blisters from running.
Nicotine reduces the blood supply to the skin, which makes it more susceptible to injury from friction. A study on soldiers that did a 161 km road march found that the smokers were more likely to suffer from blisters on their feet.
Skin temperature and the internal hydration level of the body are thought to play a role in blister formation (high skin temperature and low hydration might each increase the risk of blisters), but there has been no research yet to confirm or debunk this emphatically.
Best ways to prevent blisters when running
Research has confirmed that various types of skin lubricant reduce friction. A comparison of petroleum-based, glycerine-based, and heavy mineral oil-based lubricants found that the petroleum-based one (such as good old Vaseline) reduced friction the best.
However, after about an hour the friction started to increase with all three types, because the skin had become moist (see “Causes” above) from absorbing the lubricant. So, a lubricant would only be useful for shorter training sessions or races.
Don't slather your whole foot in lubricant. Your feet, and especially the soles of your feet, need some level of friction/traction for efficient running, so apply lubricant to the trouble spots only.
Tape or pad the trouble spots
Taping the areas of the foot most at risk of getting blisters (toes, heels, forefoot) has been shown to reduce or prevent blisters. Some types of tape work by being extremely smooth and thereby reducing the amount of friction as such. Other types are designed to absorb the shearing forces created by the friction and therefore sparing the skin from having to endure them.
Spenco and Blist-O-Ban are two of the US products mentioned in the research. Compeed is my favourite UK brand, and I can vouch for its effectiveness. They all come in different sizes, so check that you buy the correct size.
Wear two pairs of socks
A study using US Marine recruits has shown that wearing a thin polyester sock as a liner underneath the main sock reduced the number and size of blisters on their feet. This is because some or all of the friction that would have happened between the main sock and the foot is being transferred to now occur between the two socks.
Try toe socks
These socks that fit over the toes like a five-fingered glove are not for everyone, but they can be helpful for people who are prone to getting blisters between their toes.
Low friction socks – the jury is out
Sock characteristics that influence the amount of friction they produce with the skin include the material composition, the yarn structure, the knit pattern, the orientation of the knit pattern, and how thick the sock is.
A review of the available research published in March this year concluded that “there have not been many helpful simulation studies conducted in this field”.
My own literature search on the matter seemed to confirm this. There are so many different combinations of the sock characteristics mentioned above that no single study that we found tested all of them.
However, it seems that synthetic fibres might create less friction than natural fibres, and that slightly thicker socks might also be beneficial.
Choose your shoes and insoles wisely
Make sure that your shoes aren’t too big or too small. Too big, and the friction frequency will increase. Too small, and the pressure of the friction will increase. Either of these will add to the risk of blisters forming.
Studies going as far back as 1968 have shown that insoles made of closed-cell neoprene absorb some of the shearing force that would otherwise have been endured by the skin, thereby reducing the risk of blisters on the soles of the feet. (Closed cell-neoprene, unlike open-cell neoprene, has not been infused with gas to make it soft and squishy.) If this all sounds too technical, just consult a good podiatrist as they should be able to prescribe the most suitable insoles for your case.
Keep out the gritty stuff
If you’re going to be running in conditions where sand/mud/dust or e.g. dried grass stubble could get into your shoes, consider wearing gaiters. Anyone who has run the Marathon des Sable or has done orienteering will know how useful gaiters are in such conditions.
Keep your feet dry
Make sure that your feet, socks, and shoes are properly dry before you gear up for a run. In ultra distance events, regular sock changes will help to reduce the chances of your skin reaching the kind of moisture levels that lead to blister formation.
Moisture wicking socks have been shown to lower the risk of blisters, although the benefit is reduced if the sock is too thin. Socks made of synthetic fibres are better at wicking away moisture than those made of natural fibres.
Some studies have shown that applying antiperspirant to your feet for a few days before going for a run reduces moisture and therefore the risk of blisters, but others have been inconclusive. Applying antiperspirant too often may irritate your skin, which could create a new set of problems when you run.
In a study that compared the preventative roles of foot powder and antiperspirant in blister formation, the foot powder was found to be better at keeping the skin dry and therefore at reducing the risk of blisters.
Choose your battles
If you are prone to blisters when running, consider reducing the internal frictional forces of your foot bones by avoiding running on very hilly terrain or on a severe camber.
Take care of your feet and skin
Remaining properly hydrated while you’re running is important for so many other reasons, but from the above it is apparent that it could also reduce your risk of getting blisters.
If you have calluses, see if you can remove them to reduce the pressure between the shoe/sock and your foot. Toenails should be trimmed.
Stop using nicotine, and this includes vaping the stuff.
Like all the other parts of your body that get stronger with training, the skin on your feet will also get tougher and less prone to blisters the more you train (without overdoing it). A study (once again on those long-suffering US Marine recruits) showed that those who ran more than 48 km a week tended to develop less severe blisters than those who ran less than 16 km a week.
The fitter and stronger you are, the less chance there will be that you’ll lose your proper running form when you’re tired. As we have seen above, a change in your gait due to fatigue can contribute to blister formation.
This article has some handy tips for strength training for runners. The physios at sports-injury-physio.com can assess you via video call and create a bespoke strength training programme to reduce the risk of injuring yourself (blisters or any other injury) through running - this is also called a “prehab” programme.
How to treat running blisters
Can I keep on running with a blister?
It is better to avoid running with a blister.
Running with a different gait than your normal one due to blister pain could increase the risk of suffering other running injuries because your feet and legs are not used to the new running pattern.
Having to endure pain from running with a blister could affect your concentration and therefore your ability to respond to the environment around you, such as traffic or uneven terrain.
A blister that has burst because you kept on running with it can become an entry point for infection.
Protect the blister while it’s healing
Intact blisters that are not subjected to further friction or pressure should heal by themselves within a week or two.
However, having a blister on your foot, especially on the sole of your foot, means that it will inevitably experience some friction and pressure as you go about your normal business.
The best way to protect an intact blister is to stick a hydrocolloid blister plaster over it. You can find several different brands of hydrocolloid plasters, but I've always preferred Compeed. It sticks really well (even in extremely wet conditions) and feels comfortable once it has been applied.
Hydrocolloid plasters are a bit thicker than conventional plasters, so you may find that there’s too much pressure on the intact blister when you put a shoe on. If this is the case, you could cut a hole the size of the blister in a piece of hydrocolloid plaster and then stick this plaster “doughnut” around the blister. This will help to reduce the pressure on the blister roof.
Should I pop a blister?
No. You need the blister roof to remain intact to protect the wound and to keep out infection.
If the blister is very big, you could consider draining it by using a sterilised needle to pierce a small hole in the side of the blister while maintaining the blister roof. But make sure to disinfect the skin and then cover it with a hydrocolloid plaster to prevent infection. The gentle pressure from the plaster also helps to prevent the blister from filling up with fluid again.
What if a blister has popped by itself?
Disinfect it properly and apply a hydrocolloid plaster directly over it.
How we can help
Need more help with your injury? You’re welcome to consult one of the team at SIP online via video call for an assessment of your injury and a tailored treatment plan.
We're all UK Chartered Physiotherapists with Master’s Degrees related to Sports & Exercise Medicine. But at Sports Injury Physio we don't just value qualifications; all of us also have a wealth of experience working with athletes across a broad variety of sports, ranging from recreationally active people to professional athletes. You can meet the team here.
About the Author
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