What [Really] Causes Blisters On Feet?
You probably think blisters are caused by heat, moisture and friction? I'm afraid that's not really true.
Yes your foot gets hot in your shoe, yes that makes your foot sweat, and yes that moisture increases friction levels. But what causes blisters is... the skin stretching too much.
Watch the video below to see how.
Let me tell you a quick story...
One day back in 2008 I was on my morning walk. I was 8 minutes in and I started to get that familiar hot-spot feeling at the back of both heels. I tightened my laces, which relieved things a bit, and kept going. But shortly after that, I felt that familiar stinging pain of a blister.
What the ...
I was confused.
Not only was I 100% sure my foot wasn’t moving in my shoe, I had taped my heels, like I do every morning. Plus I had been walking for only 8 minutes - my feet weren't that sweaty yet. So where was the heat, moisture and friction coming from. How on earth could anything be rubbing on my skin - it was fully covered with tape!
I do my laces up tight to stop blisters - image credit
The fact is, there wasn’t anything rubbing my heel. But because of the way my heel bone was moving inside my foot, my skin was stretching up and down with every step I took. And I could feel it!
When the skin stretches (shears) too far and for too long, the connections between skin cells fatigue and break. These tiny tears under the skin surface are the start of the blister injury. Fluid fills the injured area and within 2 hours, you'll have a blister.
The relevance of heat, moisture and friction.
The popular theory is that heat, moisture and friction cause blisters. While these factors are relevant, they represent a shallow and incomplete understanding of the blister process - and an unhelpful one at that. Here's why:
It gets hot in your shoe (heat) - that's unavoidable. This makes your foot sweat (moisture) - that's unavoidable. This increases friction levels (friction) - that's unavoidable. Try keeping your feet cool and dry in your shoes when you're exercising - it's impossible!
Friction has an unfortunate double meaning: one is rubbing, the other is the force that resists rubbing. The latter definition is the one we need to use. High friction levels cause the skin, sock and shoe to stick together for a bit longer. And because the bones continue to move inside your foot, the skin is made to stretch.
Shear is normal and it happens with every step you take. Thankfully, the feet are able to tolerate a lot of it. Blisters only occur when shear is excessive and repetitive. That threshold is different for everyone ... some people are blister prone, others seem to be blister-resistant.
With your new-found knowledge of what causes foot blisters, use these resources to get you started on truly successful blister prevention and treatment.
- Reduce friction levels
- Reduce peak pressures
- Reduce bone movement - a podiatrist can help you with this
- Alter your skin’s cellular make-up to increase its resistance to blister-causing shear
Leave a comment
Also in Blister Blog
The Adelaide 6-day race 2018 was held at the scenic Thorndon Park. The running surface was cement, part of it paved, and the loop is 1.42km, with 10m elevation.