Around the world, communities have been contending with record-breaking heat waves and the life-threatening dangers that go along with them.
With long-term average temperatures on the rise, and summers getting progressively hotter in many places, the challenge of keeping people safe under extreme heat – and its comparably nefarious cousin, high humidity – will only grow more dire.
“It’s not cooling off anytime soon,” said Heidi Brown, associate professor of public health at the University of Arizona. Not too far away, in Phoenix, daily temperatures have reached at least 110°F for more than three weeks straight.
Heat stroke, heat exhaustion and heat cramps all fall under the category of heat-related illnesses. In some cases — and always in the case of heat stroke — these conditions require emergency medical attention. According to the National Weather Service, extreme heat is the top weather-related cause of death in the U.S.
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Anyone can be affected, but people who are socially vulnerable — including those who are elderly, unhoused, working outdoors, incarcerated or low-income — are at particular risk.
“We know that there’s this kind of strong relationship between poverty and poor health,” said Diana Hernández, an associate professor of sociomedical sciences and co-director of the Energy Opportunity Lab at Columbia University. “And so you have folks that are already compromised in their health status — you need cooling to be healthy and, in some cases, stay alive.”
Here’s a look at the physiological impacts of heat and humidity, what you can do if you must be outside when they strike and some resources you can turn to if air conditioning isn’t readily accessible.
How do extreme heat and humidity affect the body?
As warm-blooded mammals, our bodies must maintain a constant temperature, said Chris Uejio, an associate professor of geography at Florida State University. That temperature typically hovers somewhere between 97 and 99 degrees Fahrenheit.
“When our environment becomes hotter than our internal core body temperature, and/or we’re creating heat from metabolic activities, our body temperature will rise,” Uejio said.
If the brain senses too much heat in the body’s core, a couple different systems can kick in to cool it down. The heart can speed up to pump blood out to the extremities in an effort to transfer heat away from the core, and blood vessels can carry more blood near the skin’s surface for the same reason, Uejio explained. That allows some of that excess heat to be released into the environment.
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Good old-fashioned sweating is even more effective. When the body generates sweat, that liquid coats the skin and eventually evaporates, a process that cools us down. Uejio noted that it’s the same reason that we feel cooler after stepping out of a shower.
But when humidity is high, the air holds more water, making it more difficult for that sweat to evaporate. And when the air fails to efficiently wick sweat from the skin, it can’t take the heat with it, JohnEric Smith, an associate professor of exercise physiology at Mississippi State University.
When we get too hot and dehydrated, our cardiovascular system works harder and our kidneys are more stressed.
Who’s most at risk when it comes to extreme heat and humidity?
Older adults, young children, pregnant people and those with pre-existing medical conditions are all more vulnerable to heat. In the case of older adults, that’s in part because they’re more likely to have underlying health conditions — including some that can increase heat sensitivity — in addition to poor blood circulation.
A window-mounted air conditioning unit hangs outside a mobile home during a record heat wave in Phoenix, Arizona, July 20, 2023. Photo by Patrick T. Fallon/AFP via Getty Images Help for costly energy bills Keeping your living spaces cool when it’s hot outside can get expensive. Households where residents are low-income or Black, Indigenous or other people of color are more likely to be energy insecure, or unable to meet their energy needs and pay for necessities like air conditioning. That’s according to Diana Hernández at the Energy Opportunity Lab at Columbia University. These households might also live in homes that are poorly insulated — and therefore harder to cool — or not equipped with cooling systems in the first place, Hernández said. Both of these scenarios can jeopardize health. But there are resources available for those in need: Check out energy assistance programs. State and federal programs are available to help households pay for their energy needs. Community action agencies can connect people to those programs, Hernández said.
State and federal programs are available to help households pay for their energy needs. Community action agencies can connect people to those programs, Hernández said. Get in touch with your local utility company. They may be able to set up payment plans and offer other financial relief programs, she added, particularly for those who qualify based on their medical status or, in some cases, their income.
They may be able to set up payment plans and offer other financial relief programs, she added, particularly for those who qualify based on their medical status or, in some cases, their income. If you don’t have air conditioning at home, see if your state can help. Some states are choosing to use funds distributed through the federal Low Income Home Energy Assistance Program (LIHEAP) to help cover the costs of air conditioning systems like window units for eligible households.
Some of the medications people may take to manage those conditions, Uejio said, can also disrupt the body’s ability to regulate its temperature, as well as how hydrated they stay, in some cases.
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Infants and young children have smaller bodies, which means they can accumulate heat more rapidly, Uejio said. Kids’ ability to communicate is also more limited, he added, which can make it harder for them to alert their caregivers if they’re overheating. Smith also noted that sweat glands aren’t fully developed until children hit puberty.
Extreme heat exposure is linked with adverse outcomes in pregnancy, including preterm birth and low birth weight. Pregnant people also have an increased metabolic rate, Smith said. Their bodies have to work harder to stay cool, and they’re at an increased risk of dehydration, according to the Centers for Disease Control and Prevention.
Labor laws regarding extreme heat are patchy. Although federal standards require employers to keep their employees safe, that mandate isn’t specific to any particular environmental conditions, Uejio said. Only a handful of states have some type of occupational heat safety standards. Those standards generally incorporate three key factors, he added: water, rest and shade.
Tips for staying safe when it’s extremely hot or humid
It’s crucial not to underestimate the risks of extreme heat and humidity. Heat is notoriously sneaky. The early signs of heat exhaustion can sometimes be mistaken for general feelings of malaise or symptoms of other conditions, Uejio said.
The body is remarkably adaptable — healthy individuals can acclimate to moderately hot conditions, but that process requires time and exposure. Smith noted that many of us spend a lot of time in air conditioning when it’s hot outside, which means our bodies aren’t necessarily prepared to handle the heat efficiently.
Here’s what experts recommend: