8 Science-Backed Tips to Keep Your Feet From Burning on Hot Sand

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With temperatures hitting record highs this summer, beaches—and their promise of cool ocean dips—beckon. But to reach the waves, it's likely you'll first have to cross an expanse of foot-scalding sand. Sand is made up of decomposed rock—quartz, mostly, but also calcite, feldspar, gypsum, or basalt, sometimes with a smattering of shell, coral, or fish poop tossed in—and according to Paul Jarvis, a geologist and volcanologist at the University of Geneva, it receives solar energy via the process of radiation. The composition of sand causes it to heat up as the day progresses and to retain that heat, reaching temperatures as high as 140°F—sufficient to inflict third-degree burns. Here are tips for protecting your soles from this painful outcome.

1. WEAR THE RIGHT KIND OF SHOES.

This seems obvious, but the level of protection you get depends on the kind of shoe you're wearing. Materials such as plastic and rubber (what many soles are made of), foam resin (the stuff of Crocs), and the neoprene base of the Sand Socks that many beach volleyball players swear by provide a barrier between skin and sand. This helps cut down on conduction—the transfer of heat from the warmer surface of the sandy beach to the cooler surfaces of your feet. As a result, your feet are protected (at least temporarily) from blistering. And though they're likely the first shoes you picture when you think of the beach, flip-flops and other open shoes should be avoided on especially scorching days, because they let the hot sand in.

2. MAKE A PATH USING A COUPLE OF BEACH TOWELS.

Forgot your shoes in the car? You can protect your feet by rolling out a couple of towels to step on, repeating the process until you reach your coveted beach spot. The cotton of your towel is better at quelling heat transfer to your feet than the rubber soles of your shoes are due to what scientists call a lower thermal conductivity—“the measure of how fast heat can be conducted through the material,” Jarvis tells Mental Floss. However, your towel is also thinner than your shoe bottoms, and heat conducts faster through thin objects. In other words, you’ll have to hurry if you want to keep your feet cool.

3. RUN FAST …

The less time the soles of your feet spend touching the sand, the less time there is for conduction. But sprinting is probably a technique best reserved for covering short distances or for morning beach visits, before the sand has had a chance to soak up the solar rays for several hours and achieve maximum temperature. Because no matter how fast you run, conduction is still happening, and after some strides, your feet will eventually begin to feel the burn.

4. … OR BURROW YOUR FEET.

If you're loaded down with a cooler and tote bags, try a technique favored by professional beach volleyball players: Burrowing your tootsies as you walk, which puts your feet in contact with the much cooler sand beneath the surface. Because there are large gaps between grains of sand, it's “unable to efficiently transmit heat … through the sand bed to [its] deeper levels,” Jarvis says. So dig in a few inches. This way of “walking” is actually more of a slow shuffle, but it'll get you to your destination sans burns.

5. WET THE SAND …

It takes five times as much solar energy to heat water 1°C (33.8°F) as it does to heat sand by the same amount (what's technically known as heat capacity). So “adding just a small amount of water to the sand can dramatically increase the amount of heat the sand surface needs to receive before it gets hot,” Jarvis says. You can replicate the effect by toting a bucket of water and tossing its contents under your feet little by little as you go. While not the easiest method, it could be a solution for when you're already near the water and have to, say, run to the restroom or buy a snack. Just grab one of the kids' sand-castle buckets. Wet sand is also a lot less arduous to walk and run on than dry sand.

6. … OR YOUR FEET.

American pro beach volleyball player Sara Hughes has a go-to sand strategy: “To cool down, I personally like to put water on my feet,” she told USA Volleyball's blog. According to Jarvis, because water has a higher heat capacity than human skin, having wet—and therefore colder—feet means "you can be exposed to the beach for longer before your skin reaches a temperature at which it will burn.” Obviously, this is a highly temporary solution, since your feet will quickly dry. So bring the bucket for this tactic too: You might have to dip your feet into the water several times before reaching your ultimate destination.

7. FOLLOW THE SHADE.

Since it doesn’t take a lot of energy to change the temperature of sand, areas in shadow will feel noticeably cooler to the touch. It's easier to find those spots early in the morning or at the onset of evening, when the Sun is at an angle to the beach; the rest of the day, keep an eye out for shadowed spots made by the lifeguard chair, beach umbrellas, or palm trees to give your feet relief.

8. FIND A LIGHT-COLORED BEACH.

Should you opt to go shoe-less, choose your sand wisely. The heat capacity of the sand on any beach you visit is dependent on what minerals it’s comprised of—a challenge to know unless you do your own scientific studies, beach by beach. However, a general rule of thumb is that hotter beaches come with darker sands—and the opposite is also true. “Light-colored sand reflects, as opposed to absorbs, a significant proportion of the Sun’s radiation,” Jarvis says. “Dark sand, such as that originating from volcanic rocks [like basalt], is much more heat absorbent, meaning it will heat up quicker and therefore, potentially become much hotter.”

Why Does Humidity Make Us Feel Hotter?

Tomwang112/iStock via Getty Images
Tomwang112/iStock via Getty Images

With temperatures spiking around the country, we thought it might be a good time to answer some questions about the heat index—and why humidity makes us feel hotter.

Why does humidity make us feel hotter?

To answer that question, we need to talk about getting sweaty.

As you probably remember from your high school biology class, one of the ways our bodies cool themselves is by sweating. The sweat then evaporates from our skin, and it carries heat away from the body as it leaves.

Humidity throws a wrench in that system of evaporative cooling, though. As relative humidity increases, the evaporation of sweat from our skin slows down. Instead, the sweat just drips off of us, which leaves us with all of the stinkiness and none of the cooling effect. Thus, when the humidity spikes, our bodies effectively lose a key tool that could normally be used to cool us down.

What's relative about relative humidity?

We all know that humidity refers to the amount of water contained in the air. However, as the air’s temperature changes, so does the amount of water the air can hold. (Air can hold more water vapor as the temperature heats up.) Relative humidity compares the actual humidity to the maximum amount of water vapor the air can hold at any given temperature.

Whose idea was the heat index?

While the notion of humidity making days feel warmer is painfully apparent to anyone who has ever been outside on a soupy day, our current system owes a big debt to Robert G. Steadman, an academic textile researcher. In a 1979 research paper called, “An Assessment of Sultriness, Parts I and II,” Steadman laid out the basic factors that would affect how hot a person felt under a given set of conditions, and meteorologists soon used his work to derive a simplified formula for calculating heat index.

The formula is long and cumbersome, but luckily it can be transformed into easy-to-read charts. Today your local meteorologist just needs to know the air temperature and the relative humidity, and the chart will tell him or her the rest.

Is the heat index calculation the same for everyone?

Not quite, but it’s close. Steadman’s original research was founded on the idea of a “typical” person who was outdoors under a very precise set of conditions. Specifically, Steadman’s everyman was 5’7” tall, weighed 147 pounds, wore long pants and a short-sleeved shirt, and was walking at just over three miles per hour into a slight breeze in the shade. Any deviations from these conditions will affect how the heat/humidity combo feels to a certain person.

What difference does being in the shade make?

Quite a big one. All of the National Weather Service’s charts for calculating the heat index make the reasonable assumption that folks will look for shade when it’s oppressively hot and muggy out. Direct sunlight can add up to 15 degrees to the calculated heat index.

How does wind affect how dangerous the heat is?

Normally, when we think of wind on a hot day, we think of a nice, cooling breeze. That’s the normal state of affairs, but when the weather is really, really hot—think high-90s hot—a dry wind actually heats us up. When it’s that hot out, wind actually draws sweat away from our bodies before it can evaporate to help cool us down. Thanks to this effect, what might have been a cool breeze acts more like a convection oven.

When should I start worrying about high heat index readings?

The National Weather Service has a handy four-tiered system to tell you how dire the heat situation is. At the most severe level, when the heat index is over 130, that's classified as "Extreme Danger" and the risk of heat stroke is highly likely with continued exposure. Things get less scary as you move down the ladder, but even on "Danger" days, when the heat index ranges from 105 to 130, you probably don’t want to be outside. According to the service, that’s when prolonged exposure and/or physical activity make sunstroke, heat cramps, and heat exhaustion likely, while heat stroke is possible.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

This article has been updated for 2019.

Chimpanzees Bond by Watching Movies Together, Too

Windzepher/iStock via Getty Images
Windzepher/iStock via Getty Images

Scientists at the Wolfgang Kohler Primate Research Center in Germany recently discovered that, like humans, chimpanzees bond when they watch movies together, the BBC reports.

In the study, published in Proceedings of the Royal Society B, researchers stationed pairs of chimpanzees in front of screens that showed a video of a family of chimps playing with a young chimp. They found that afterward, the chimps would spend more time grooming and interacting with each other—or simply being in the same part of the room—than they would without having watched the video.

They gave the chimps fruit juice to keep them calm and occupied while they viewed the video, and they chose a subject that chimps have previously proven to be most interested in: other chimps. They also used eye trackers to ensure the chimps were actually watching the video. If you’ve ever watched a movie with friends, you might notice similarities between the chimps’ experience and your own. Drinks (and snacks) also keep us calm and occupied while we watch, and we like to watch movies about other humans. Since this study only showed that chimps bond over programs about their own species, we don’t know if it would work the same way if they watched something completely unrelated to them, like humans do—say, The Lion King.

Bonding through shared experiences was thought to be one of the traits that make us uniquely human, and some researchers have argued that other species don’t have the psychological mechanisms to realize that they’re even sharing an experience with another. This study suggests that social activities for apes don’t just serve utilitarian purposes like traveling together for safety, and that they’re capable of a more human-like social closeness.

The part that is uniquely human about this study is the fact that they were studying the effect of a screen, as opposed to something less man-made. The chimps in question have participated in other studies, so they may be more accustomed to that technology than wild apes. But the study demonstrates that we’re not the only species capable of social interaction for the sake of social interaction.

[h/t BBC]

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