A Deep Cut

I haven’t been doing much hiking lately—I’ve just had other things to do and I haven’t made it as much of a priority. But I made it to Hocking Hills last week to do about 8½ miles, and then yesterday I went to Great Seal State Park and did about 5 miles.

And at Great Seal I had something happen that hasn’t happened in along time: I sliced the sole of my foot.

It happens every once in a while. Never in a store or any place of business (so their paranoia is totally unjustified), but occasionally when I am hiking. In fact, when I am hiking sole damage has almost always happened when I was off bushwhacking off-trail.

Those injuries usually end up being what I call a “flap-injury”. Generally, the skin on the bottom of the foot is so tough that when something (like a broken off twig stump on a larger stick) manages to break the skin, it tears off in a flap. Often, I won’t even notice them when they happen; but in crossing a creek I’ll suddenly feel a bit of a sting.

These injuries also tend to occur on or near the arch of my foot. The skin on the ball or heel (or even the outer arch of the foot) tends to be too keratinized to have that happen to it.

But this injury was a real slice. I measured it: it went down 1.9 millimeters.

It is interesting the difference between hiking at Hocking Hills and Great Seal. Hocking Hills is almost all sandstone, and because of the deep gorges there tend to be a lot of hemlock trees, which produce a bunch of needles that are a joy to walk on. The trails are almost all made up of friendly, twig-covered dirt, and the rocks are a smooth and large sandstone that is easy to walk on. So, at Hocking Hills, 8½ miles was easy to do, even though my feet weren’t well-conditioned.

Great Seal, on the other hand, is in a region of Ohio with a lot of exposed shale. Shale chips, and shale is sharp. So even after a few miles I was feeling it a bit on my soles. Nothing too bad, and after a bit more hiking my soles eased into it.

Anyways, at about the 1½ mile mark I actually sliced the sole. On what I have no idea; I just suddenly felt a sharp stabbing. I didn’t notice any immediate blood, and just kept on hiking without feeling any discomfort.

But as I said, when I got home later I measured it: 1.9 millimeters.

Now, when you check resources, it’s tell you that the stratum corneum on the sole goes up to 600 microns thick. For instance, in article from Science in 1966 devoted specifically to “The Skin”, they show you this picture of skin thickness on various parts of the body.

Different Skin Thicknesses

And here’s the text describing the picture:

Equally important, though much less obvious, are the striking differences in thickness of constituent skin layers in different regions of the body. The remarkable differences in dermal thickness are depicted schematically in Fig. 1C. Epidermal thickness, 60 to 100 microns, is remarkably constant over the body, except on the palms and soles, where the stratum corneum alone may reach 600 microns in thickness.

The dermis is the underlying part of the skin with all the nerves and glands and blood vessels. The epidermis is the outer layer, and includes the stratum corneum, which is the keratinized portion which is a lot harder than the rest of the skin and does the major job of keeping stuff out.

It is also the part that gets a lot thicker when it gets regular pressure (or heat), like on the soles of our feet when we walk barefoot. (The corneum part is also related to the word corn, which form from localized pressure from shoes.)

So, according to Science, that stratum corneum on my heel could reach up to 600 microns, that is, 0.6 millimeters. Since the slice went down 1.9 millimeters, I guess that meant I was in real trouble.

And I didn’t even get the thick part of my heel. I got the part where the arch was converting to the heel. It wasn’t on the thick part of my heel. Here’s a “cleaned-up” picture of my sole so you can see where the slice was.

Location of the Deep Cut

So I guess that meant I went really deep into the dermis, and beyond.

But not so fast. Wikipedia tells us that the epidermis is “thickest on the palms and soles at 1.5 mm (0.059 in).”

Oh, OK. So at 1.9 millimeters I guess there’s less penetration than if sole depth was 1.5 millimeters rather than 0.6 millimeters (and even if it wasn’t over the thickest part of my heel).

But I’m hurting, right?

Well, to tell you the truth, I didn’t even notice anything again until I got home, and in just a few situations (like climbing stairs and hitting my foot just right). That’s when I looked more closely. Here’s a shot directly into the slice as I open up the skin.

Looking into the Deep Cut

It didn’t even bleed at all. The slice didn’t make it through my stratum corneum. The slice went close enough to the dermis so that if a particular step pulls things apart, I feel it. But my inner skin, the important stuff, is intact.

But why would these resources think I should be bleeding?

Because they never see anything but normally-shod people, that’s why.

They really have no conception of what a normal foot looks like. All the feet they’ve ever seen are abnormally affected by constant shoe-wearing.

You have to look at non-Western studies (and non-shod feet) to find out what useful soles do. For instance, in the 1958 “A Comparison of Foot Forms Among the Non-Shoe and Shoe-Wearing Chinese Population”, by Lam Sim-Fook and A. R. Hodgson, it says:

The feet of the non-shoe-wearing population showed thick soles with prominent skin creases apart from many minor lacerations due to traumata. The pachydermatous skin on the sole of the foot had an extraordinarily thick keratinized layer about 0.5 to one centimeter thick which permitted the individual to walk about without any discomfort.

That’s 5 to 10 millimeters of sole thickness.

So it’s not surprising that my “deep cut” didn’t amount to anything. My feet are more like “normal” (or should I say “natural”) feet.

The only reason I even noticed anything at all was because I didn’t get the bottom of my heel. There, as the article alludes to, my stratum corneum is a lot thicker, 4-5 millimeters, I estimate.

That’s the sort of feet that provide their owners with a lot of protection that most shoe-wearers just don’t get.

And I guess we can see, maybe, why store-owners get so paranoid.