Some people swear callouses keep them blister-free and build them with pride. Others get them shaved off. So, do callouses protect against blisters?
Do callouses on your feet prevent blisters? Some athletes swear they keep them blister-free and build their callouses with pride. Others get regular pedicures to keep the hard skin away, especially just before a race. So, do callouses protect against blisters?
What Is A Callous?
Callouses are a thickening of the stratum corneum – the very outer layer of the skin. Thickening of the corneum is one adaptive change research has shown to occur when the skin is subjected to repeated low level shear distortions. I go into further detail in this post.
Do Callouses Protect Against Blisters?
Callouses DO protect against abrasions. An abrasion occurs when something wears through the skin - from superficial layers into deeper layers. Like when you fall off your bike and scrape your knee along the road. A callous protects against this because there is more corneum to wear through before getting to raw skin.
But blisters are not a superficial-to-deep wear injury. They're a mechanical fatigue of a skin layer a few layers deeper than the corneum (the stratum spinosum). When there's too much skin stretching of the skin, the structural connections hear tear. Fluid then fills the injured space to form a blister.
A callous can reduce shear stress to some degree. Sanders et al (1995) reviewed the literature on the skin’s response to shear and friction. This included studies conducted on the skin of the palms (Bennett et al, 1979), thigh (Rubin, 1949), anterior tibial surface (Naylor, 1955 ), back, buttocks, shins, forearms upper arms, thighs, palms and soles (Sulzberger et al, 1966), the palms and soles of monkeys (Cortese et al, 1969), mouse ears (MacKenzie, 1974 ) and rat gums (Carter, 1956). They summarise the adaptive changes leading to increased resistance to epidermal fatigue:
The results suggest mechanisms and processes for adaptation to frictional stress. The cells at the basement membrane increase in size, density, and speed of transport across the epidermis, increasing thickness of the stratum corneum layer. The thickened stratum corneum means that there is a greater volume through which to distribute the shear load between the skin surface and immediately above the basement membrane. With a greater volume of stratum corneum, shear stress gradients are lower; thus, the skin is at lower risk of failure.
However, as tempting as it might be to build thick chunky callouses over blister prone areas, excessively thick callouses are not entirely protective of blister formation. What’s more, they can make blisters very difficult to deal with.
Blisters Under Callouses
In fact, the presence of a callous often makes blisters worse. The reality is, a little bit of thickening can be good, but callouses are far from protective. And a blister under a callous are nasty! They’re very painful and they’re difficult to manage.
How Much Callous Is Good?
We want to benefit from the adaptive thickening that makes the skin more resistant to blisters. But we don’t want to have to build chunky callouses that make blisters more likely. The right amount of skin thickening is barely noticeable.
How Do You Get Rid Of Callouses?
To reduce the likelihood of blisters, it is advisable that you either see a podiatrist to debride callouses to the right degree. Or maintain them yourself with the use of a pumice stone or emery board. The aim is to reduce the excessive buildup.
If you're not too keen on that, you can deflect pressure from your callous by using a felt donut pad. Rather than moleskin, which is far too thin to deflect enough pressure, go for podiatry felt. Here's the 5mm thick Hapla Podiatry Felt we use.