Anatomy of a callus
Most musicians have a pretty good idea of what calluses are, since they develop them without noticing and take them for granted. Yet, what's actually going on to create a callus is actually pretty amazing.
-The outer layer of your skin is called stratum corneum, and it's function is to prevent the interior tissues from stress and damage. The skin itself has many layers from outside in: stratum corneum, stratum lucidum (hands and feet), stratum granulosum, stratum spinosum, and stratum germinativum. Even if none of those names mean anything, this area of skin, the epidermis, has no blood vessels and no blood supply. The epidermal cells are created from deeper tissues, rather than superficial ones.
- This stratum corneum's response to mechanical irritation or stress is to reinforce the area to protect it, and the action is called hyperkeratosis.
-Calluses are a sign that you've adapted your body to this stress (musical instrument, holding a pen, weight lifting) over time, and is actually a good thing! If one takes on a mechanical stress too quickly, a blister will ensue. In addition, a callus is an area of strength and fortification, and not something that needs to be removed or avoided. (I've seen people try to cut off their finger calluses-yuck!)
"Callused skin is actually an area of strength in skin that has much better circulation than other areas and are a necessary part of the kinetic chain when it comes to movement. But wait! You thought that a callus was something that was unhealthy, right? When you get a little callus, because of repeated friction (like a corn on your toe or a tiny area of callus on the sole of your foot), this small patch of “health” becomes like a rock in a shoe (or a pea under a mattress if you’re a princess). Ideally, calluses should be developed widely — across the entire palmar surfaces of the hands and feet. We need strength in these tissues to really optimize the whole-body strength actions of both the upper and lower body".- Katy Bowman
- A friction blister (as opposed to sun or other type) is a splitting of those layers of epidermis, almost like a shearing, which occurs from a quick change in mechanical stress. Fluid (not blood) accumulates in between the layers. We know this from poorly fitted shoes, and for most string players, in pizzicato passages.
-If a hand/finger/foot callus is getting painful or disrupting your movement, use a pumice stone after showering or bathing. Please don't try to hack it off with fingernail clippers in public-It's gross.