Extreme heat can harm your health in more ways than you think.
Heat stroke and dehydration are often the first health risks to come to mind when you think of heat waves. But the reality is much worse: There are no less than 27 ways that a heat wave can kill you, according to a groundbreaking 2017 study led by Camilo Mora, Ph.D., a professor of geography at the University of Hawaii.
“Until recently, [researchers] really only looked at heat waves in terms of mortality — just the numbers of deaths,” says Mora. “We did something different. We decided to ask one question and study it for a semester.”
That question was how. How does a heat wave kill someone? As soon as Mora, his colleagues, and students began digging, they realized that the more apt question was probably: How does heat not damage a person? “We started realizing that there are organs in the human body that are critical, right?” says Mora. “You know, you cannot live without a brain, you cannot live without kidneys or heart. So, any damage to those organs is lethal. And then it turns out that the heat triggers different mechanisms that affect those organs.”
How the Body Deals with Extreme Heat
From the moment you step outside your home into high temperatures, your body begins working to keep you cool. “The body has this organ in the brain called the hypothalamus, which is like the body’s thermostat — it senses that it's getting hot,” says Mora. “It thinks, ‘Oh, we are in an emergency state. We need to cool down now.’ So it starts suppressing the blood flow to organs, taking that blood and sending it to the skin. This is when, particularly for white people, the skin begins to turn red. Then we begin to sweat, the sweat evaporates, which cools down the blood, and then the blood comes back down into the body — back into the organs.”
But when your blood can’t cool down, like when you’re outdoors for a prolonged period in extreme heat, it doesn’t return to the organs — and that’s where Mora’s 27 lethal pathways come into play.
“I’ll give you a couple of examples that often surprise people,” says Mora. “First, the stomach. You’re in the middle of this war that you’re fighting — because extreme heat is a war — and you’re not getting blood flow to your stomach. If those conditions persist, it creates anoxic and chemical conditions that then break the lining of your gut. So, anything you’ve had for breakfast is now circulating through your bloodstream. Your cells attack, and then that clogs the kidneys. Another one that happens to athletes a lot is when they get very physical when they’re doing a lot of exercise in a heat wave — they overheat their body, oxygen leaves their organs, and it’s their muscles that start to break down. These muscles have some proteins in them, and as they go into the bloodstream, they clog the kidneys as well.”
Moreover, research shows that repeated heat exposure over time can have serious health consequences. Mora cites research on sugarcane workers, who often spend long hours under the beating sun. “We see that they have higher rates of kidney failure — repeated heat exposure causes the kidneys to shut down over time,” he explains.
The body simply can’t function in high heat, and every minute of exposure can negatively affect you. “I used to say that dying from a heat wave is like a horror movie with different endings — but each one is just as terrifying as the other,” says Mora.
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When Does Hot Weather Become Too Hot?
According to Mora, the answer to this question varies to a certain degree, depending on age, health, and lifestyle factors. “There are sectors of society that are affected more than others. The least resilient are older adults, followed second by children,” he notes. “We also know that people who have compromised their systems, such as alcoholics and drug users, are at a higher risk. “
Adults with no pre-existing conditions fare better, certainly, but that’s not enough of a reason to plan an outdoor run on a triple-digit day — especially when you could hit a treadmill at your Equinox Club instead.
Generally, you’re at risk of experiencing harmful side effects when the outside temperatures rise above your internal temperature. “You start seeing people struggling at 32°C [89.6°F],” says Mora. “People might endure all the way up to 38°C [100.4°F]. But the process by which the body suppresses oxygen to the organs has already started, even if it is not a lethal risk.” For Mora, that’s reason enough to skip the outdoor workout.
How to Protect Yourself in a Heat Wave
The easiest way to protect yourself from extreme temperatures: Don’t ignore heat wave warnings. “We have become better at not dying from this, despite the fact that the conditions remain lethal,” he says. “For instance, AC is a lifesaver device. Also warning systems, which are not available in many parts of the world, but are in the U.S. These adaptations are happening. But the only way those systems work is if we respect them.”
If you must be outside during a heat wave, find and stay in the shade. “The sun is an additional source of heat,” says Mora. “And in a hot situation, the last thing that you want to do is to get more heat. I’m not saying you should never go into the sun because that’s a natural condition. But in a heat wave, why compound something so dangerous?”
Remember to stay on top of your water and electrolyte intake — even if you don’t feel thirsty — wear lightweight, loose clothing, and stop all activity if your heart feels like it's pounding or you’re gasping for breath, according to the Centers for Disease Control and Prevention.
Mora has adapted his own behavior, making more cautious choices when he knows he’ll be outside on hot days. “I am Colombian, and I grew up on a farm where I worked outside all the time. [Heat exposure] never crossed my mind when I was working from 6 a.m. to 4 p.m. in the fields,” he says. “You know, now I start feeling my kidney stop processing like nobody's business. Now I protect myself — if I’m outside, I avoid being directly in the sun, because you are only taking in more heat. I watch it a lot now.”