When I wrote about Dirty Feet, it generated a comment (a question really) asking what I did to maintain them.
Here’s the answer.
As part of that posting, I showed a photo of my own soles on a hike in Hocking Hills.
That prompted a question from unci narynin:
Looking at your “hiking soles” I noticed another thing, how smooth the skin is. Do you do anything against the rough edges? (I use a file every couple of days . . . on dry clean skin.)
I will very occasionally use a foam sanding block.
They’re nice in that the foam will bend around the curvature of the sole, particularly in the heel area.
But as I said, I don’t use it very much—I do two other things that minimize my need for them and really do prevent cracks.
The first one I’ve written about before.
That’s using a foot cream that contains urea, which is critical in keeping the skin moist. According to “Comparison of Salicylic Acid and Urea versus Ammonium Lactate for the Treatment of Foot Xerosis,” Jennings, M.D., et al., J Am. Podiatr. Med. Assoc. 1998 Jul; 88(7):332-6,
The stratum corneum must contain more than 10% water to remain soft and pliable; when the water content drops below 10%, it becomes rough, with possible scaling and cracking.
The stratum corneum (literally, “the horny layer”) is the outermost layer of the skin. And urea is a very important component is helping the skin retain its water. According to “Urea analysis of extracts from stratum corneum and the role of urea-supplemented cosmetics”, Häntschel, D., et al., J. Soc. Cosmet. Sci., 49, 155-163 (May/June 1998),
Urea is one of the most important soluble substances of the stratum corneum. In recent years this substance has become more and more important in dermatological therapy and cosmetics. Many diseases have been described that are characterized by a deficiency of urea, such as atopic dermatitis or clinical dry skin. The urea content of normal skin is nearly 1%. It contributes in a significant manner to the hydration of the stratum corneum. Besides amino acids, lactate, and other substances, urea contributes approximately 3-7% to the natural moisturizing factor (NMF). The NMF appears to be responsible for the hydration status of stratum corneum. Otherwise urea is known for its keratolytic and pruritus-easing properties, and it is a very potent humectant in moisturizing creams. Its sources in the epidermis are sweat and the decomposition of arginine by arginase during the process of keratinization.
So there’s a lot of research on this.
When it looks like my heels are thinking about cracking (and other times if I think about it), I’ll apply either Flexitol Foot Balm or Gold Bond Foot Cream. The former is less oily and the latter moreso. I tend to prefer the Flexitol simply because it isn’t so oily, and as far as I can tell, oil doesn’t seem to be all that important in keeping the skin on the feet moisturized (it does more to keep it oil-ized). However, if I know I’m going out in particularly wet conditions, then I will go with the oilier Gold Bond, because then the oil protects against that.
But there is something else that I’ve discovered that seems to work really well in stopping heel cracks from developing. I return, once again, to the Seri Boot.
As I’ve mentioned before, particularly over the winter when I really didn’t get out hiking much (and this past winter was pretty bad), I’ve been baking a Seri boot, which consists of standing on heated sand until it just starts to get painful. The temperature of the sand is around 190°F (90°C), though that has increased since I started doing it. (If you try it, be careful not to burn yourself—you have sensors on your soles for a reason.) In reacting to the heat, the sole produces some really nice callous, or as I like to put it, natural padding.
I have found quite a few benefits to doing this. The increased callous means my soles didn’t soften up over the winter, so that when I went to Easter Island I was quite capable of hiking for quite a distance without getting footsore. It also gave me, not unsurprisingly, good heat-resistance, so that I was able to walk on the hot sidewalks of Easter Island with much trouble at all. It also helps turn the plantar skin into a nice, supple leather, as you can see in the first picture.
It has also helped me with tennis.
Let me explain: I normally play tennis about 2 hours per week. But lately I’ve been playing more, and playing more tennis means that I tend to wear off the callous quite a bit faster than, let’s say, simply walking on concrete. After all, in tennis, one is making all sorts of quick stops and starts and reversals of direction. It’s the exact opposite of what one does for long distance running, in which good form has one carefully lifting up and putting down one’s feet. (By the way, tennis trains the feet, and the skin, differently, giving it good lateral strength.) When I played too much tennis the soles of my feet, particularly in the ball area, wore down faster than my body could regenerate it.
That doesn’t happen any more since I’ve been using the Seri boot treatment. I’ll play upwards of 6 hours per week without wearing down the ball of my foot.
Anyways, back to heel cracks, I seem to get them even less often since I’ve been fiddling with a Seri boot. My guess is that there is some sort of annealing going on. That’s really not quite the right word, but I think it gets across the concept.
A better example may the the sort of fire-hardening that ancient humans did making wooden spear tips. The heat treatment chemically changes the composition of the wood, drying it, making it harder, and making it much more water resistant. It turns out that such a spear point has only about 10% less penetration than a stone point.
I suspect that the high heat on the plantar skin does something similar—it help seals in the moisture of the skin below while also hardening the outermost layer and helping it resist cracking.
I tried looking to see if there was any research on this, but failed. I suspect nobody has even considered looking at it.
But I did serendipitously find an interesting research paper on fire-hardening a wooden spear tip, “Initial observations from experiments into the possible use of fire with stone tools in the manufacture of the Clacton Point,” Fluck, H. L., Lithics (2007) 28:15-19. It has a nice picture of the fire-hardening.
Of course, those making spears would have most likely been barefoot. But I found something more.
Heather Fluck (the author of the article) is now the Senior Archeologist of Hampshire County (England) (at the time of the paper she was working on her Ph.D.). The Clacton Point work was done in Denmark, at the Lejre Land of Legends, a kind of living museum. And there are pictures of her demonstrating ancient skills.
For instance, this picture on flickr shows her butchering with stone tools.
There is also this picture, on the Land of Legends site, chopping an antler.
Finally, I suspect that the bare foot in the research paper photo is also Dr. Fluck’s. Here’s another picture from flickr, again at the Land of Legends, showing her with spear(?) in hand.
It’s always fun to accidentally discover, in a different context, somebody who pretty obviously prefers to go barefoot.
Anyways, back to the original question (remember that?), let me summarize: foam sanding blocks, urea creams, heat-hardening and sealing with the Seri boot.
It works for me.