When someone starts living barefoot or going barefoot most of the time, their soles will, over time, get thicker and tougher, and there will likely be some additional tolerance to some very warm or hot surfaces that may not have been possible before without discomfort.
Skin on soles will burn
Regardless of how thick or tough soles can become, the fact remains that human skin will start to burn at a certain threshold temperature within a short period of time, and skin can never adjust to withstand that.
The National Institute for Standards and Technology (part of the U.S. Dept. of Commerce) has stated that at 118°F (48°C), human skin can sustain first-degree burns; and second-degree burns can occur at a skin temperature of 131°F (55°C).
Most pavement materials can get much hotter than the ambient temperature
How hot certain types of pavement get relates to both their color and their thermal mass. Thermal mass is the innate ability of a material to absorb, store, and release heat, depending on its composition as well as density. Higher density generally means higher thermal mass. Thermal conductivity (how easily the heat travels through the material) is also a factor in thermal mass. These various factors can become somewhat scientifically complex, with the specific details being beyond the scope of this article.
As a practical matter as related to walking barefoot, we know that asphalt, concrete, bricks, sand, and similar materials can easily absorb the heat of the summer sun and become much hotter than the ambient air temperature.
Asphalt and concrete, common paving materials, can get very hot
Asphalt and concrete, probably the most common types of pavement barefooters may walk on, each easily absorb heat from direct sunlight and retain it for a long period of time, causing the surface temperature of each to usually be much greater than the air temperature.
Asphalt, generally due its darker color, absorbs the most heat and retains that heat for a long period of time. Concrete is usually a lighter color and therefore doesn’t absorb quite as much heat as asphalt.
How much heat is absorbed into surface materials and how hot they will get also depends upon the angle of the sun. The closer a location is to the equator, the higher the average sun angle is, and the more heat is absorbed into surface materials from the summer sun.
In the southeastern United States, for example, it’s been estimated that the surface temperatures of concrete on a clear day in the middle of summer can be as high as about 30°F (17°C) greater than the air temperature. So at 85°F (29°C) air temperature, for example, most sidewalks would likely measure around 115°F (46°C) – quite hot, but probably tolerable for bare feet.
Asphalt temperatures in the same area under the same clear sunlight conditions of summer have generally been estimated to reach as much as 45°F (25°C) hotter than the surrounding air temperature. Some isolated reports have shown asphalt even up to 60°F (34°C) hotter. So if the mid or late day air temperature on some cloudless day is 85°F (29°C), an asphalt parking lot could potentially be 130°F (54°C), or even higher – well above first-degree skin burn temperature and approaching second-degree skin burn.
An interesting chart showing those potential temperatures can be found in this recent article “How hot does pavement get in the summer.”
Determining how hot some surfaces are can be easily estimated
Of course, most people don’t go around carrying an infrared thermometer designed to measure surface temperatures. And that isn’t necessary to determine if certain pavements are just too hot to walk on barefoot. You just have to feel of it with your feet.
Or if you know the air temperature, you could estimate the temperature of pavement in the hot sun of the summer by adding about 30°F (17°C) to that for concrete or adding about 45°F (25°C) for asphalt. That could vary, of course, depending on your location’s proximity to the equator – in other words, how direct the angle of the sun is in your location.
Dirt or sand can get almost as hot as concrete
Sometimes even “natural” surfaces like dirt or sand can absorb so much heat in mid-summer that they become intolerable to walk barefoot on. How hot sand can get depends upon its color, but its capacity to heat up in the direct sunlight of summer approaches that of concrete.
I remember an experience I once had where my being barefoot on hot sand became very problematic.
Back in July of 2011, my wife and I spent a few days with family at Myrtle Beach (SC). On one day, we decided to spend all day on the beach. It was stifling hot, but the water felt great. I was the only one of the bunch that had walked out to our canopy on the beach with no footwear on.
So at about mid-day, we decided to go back to the condo for a quick lunch. We had to walk about maybe 150 feet in the hot sand, which immediately began to burn my feet. I told the others I had to run, so I took off. It was almost unbearable. When I got to a place about halfway there where there was a grassy area, I stopped, thinking it might be cooler. It wasn’t. It was even worse. So I sprinted as fast as I could to the wooden area next to the condo building where there was a shower to rinse off sand.
I have to say, I had walked on hot surfaces before, but nothing like that. It was the worst pain I’d ever experienced on my feet. I was almost sure I’d have burn blisters on my feet, and they’d probably be messed up the rest of the time we were there. But amazingly, after I ran cool water on them (I looked to see if there was skin coming off or something like that), they felt fine. And after that, they still felt fine. There was absolutely no damage at all that I could tell – possibly due to the skin on my soles being so thick and tough, I’m not really sure.
Nevertheless, later walking back onto the beach, I did wear flip-flops. My wife laughed at me and said she was going to take a picture of me walking in flip-flops to show the world (fortunately, she didn’t).
Here are some tips for dealing with unexpected hot surfaces in a parking lot
If you happen to be barefoot in a parking lot or similar place and you find it’s just too hot to stand or even walk comfortably, get off that surface as quickly as you can. Walk quickly or even run from one shady spot to another.
In parking lots or at street crossings, the white painted lines are almost always cooler than the other surfaces, so walking on those lines will usually help you tolerate the hot surface until you can get off of it.
One thing that might be helpful to do if you have no choice but to stand on the hot surface for a few minutes, is to somewhat alleviate the pain by putting your weight on the parts of your feet that have the thickest skin. The heels have the thickest skin, so try standing on your heels with the front parts of your feet up off the surface. The next thickest skin is on the outside edges, so you could rotate your feet so all the weight’s on those outside edges. The front part of your feet and your toes have the thinnest skin, so you’ll want to try to keep those parts off the surface if you can.
Don’t risk getting ‘trapped’ where your feet can be burned
Don’t risk getting “trapped” on some large expanse of surface that may become extremely hot after you are already there (such as in the example I mentioned above at a beach). Having some emergency footwear available when going to such places in the heat of summer may be a wise decision.
I can remember another example where I almost got “trapped” on hot pavement. This took place around July of 2004. My wife and I attended the Orange County Fair in California, one that I had been to many times before, and always barefoot. That particular day, it was so hot that I began noticing it was getting very uncomfortable to walk on the sunny parts of the asphalt, so I tried to stay in shady areas as much as possible.
When we decided to go home later that afternoon, after leaving the gate, we had to walk over a large uncovered asphalt expanse to get to the parking lot. As I walked, I could tell that the pavement was so hot that my feet would likely be burned if I continued.
Luckily, due to the prior weather forecast and potential heat, I had brought along a pair of flip-flops just in case of such an emergency. I donned them to wear for the remainder of the distance to our car. I think sometimes the availability of emergency footwear for such weather related purposes is prudent. I know my feet likely would have had first-degree degree burns had I continued barefoot on such hot pavement.