Calluses are a thickening of the stratum corneum – the very outer layer of the skin's epidermis.
Thickening of the corneum is one adaptive change research has shown to occur when the skin is subjected to repeated low level frictional forces. I go into further detail in this post.
- Some athletes build calluses with pride and swear they keep them blister-free.
- Others get regular pedicures to keep the hard skin away, especially just before the race.
Do calluses protect against blisters?
Calluses protect against abrasions. An abrasion occurs when something wears through the skin - from superficial layers into deeper layers. A callus protects against this because there is more corneum to wear through before getting to raw skin.
But blisters aren’t 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 (shear) of the cells in this skin layer, the structural connections tear. Fluid then fills the injured space to form a characteristic blister. A callus doesn't prevent this mechanical fatigue. Skin shear happens in exactly the same way whether there's a callus or not (if not worse!).
The reality is, calluses are far from protective. And blisters under a callus are nasty! They’re very painful and they’re difficult to manage.
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 calluses that make blisters more likely. The right amount of skin thickening is barely noticeable.
To reduce the likelihood of blisters, it is advisable that you either see a podiatrist to debride calluses to the right degree. Or maintain them yourself with the use of a pumice stone or emery board. And a final tip: Moisturisers won’t make calluses any less blister-causing. That’s because the moisturiser will increase friction levels, which cause blisters. The aim is not to keep a callus soft, but to reduce its thickness.
Written by Rebecca Rushton
Rebecca is an Australian podiatrist with over 20 years experience. She has spent a lifetime dealing with her own blister prone feet in her sporting and everyday life. Rebecca specialises in helping athletes and sports medicine professionals figure out how to manage foot blisters with ease. And for kicks, she enjoys providing blister care at multiday ultramarathon events.
Rebecca is the founder of Blister Prevention and author of both "The Blister Prone Athlete's Guide To Preventing Foot Blisters" and "The Advanced Guide to Blister Prevention".