The Health Risks of Extreme Heat—And How to Assess Your Risk

Blistering temperatures aren’t just uncomfortable. It can become deadly quickly. According to some research, the number of deaths from heat-related causes will continue rising as the climate changes make extreme heat more prevalent.

Here’s what you need to know about the health risks of extreme heat and how to understand your own risk.

What happens if the body heats up?

The tropical environment in which human beings were born allowed them to tolerate heat by exchanging it through their skin. But when the air gets hotter than skin temperature (which is typically 97-99° F) or if sweat doesn’t evaporate, “we start to gain heat, and our body core temperature—the temperature of our deep body tissues—starts to rise,” says W. Larry Kenney, a professor of physiology and kinesiology at Penn State University who studies human temperature regulation. “If that rise is unabated, and it keeps going up, in some people it can lead to heat-related illnesses.”

Certain people are more at risk than others

Everyone is vulnerable to heat-related health problems, but some are more at risk than others. According to the Environmental Protection Agency, children and infants are especially vulnerable to heat-related illnesses. They lose fluid faster than adults, and must rely on their caregivers to cool them. Some medications may make it more difficult to handle heat. Antidepressants, like antipsychotics, may cause sweat to be lessened. Drugs for heart disease such as ACE inhibitors and antidepressants, which can also affect sweat production and dehydration, can lead to kidney damage. Senior citizens are at greater risk of developing diabetes or other health issues. Also, their bodies will react to heat differently than the bodies of younger individuals. Kenney points out that they produce less sweat per glyceum and their blood vessels become smaller as we age. This makes it more difficult for blood to flow to the skin to cool us down and helps to keep our blood sugar levels in check.

This can lead to heatstroke

Heatstroke happens when the body reaches a core temperature of at least 104° F, which can lead to organ failure, brain damage, and even death. It can also cause cognitive impairment. Patients with heatstroke often “don’t know where they are, how they got there, they don’t know what day it is. Eventually, they may lose consciousness, and if their body temperature continues to rise, they would eventually die,” says Kenney.

Those most vulnerable to heatstroke include older people and children, but even younger adults can get heatstroke if they don’t take steps to cool off. It most often affects people who work outdoors, military personnel, and athletes who “may ignore warning signs and keep pushing on with intense physical activity,” says Kenney. People are often more vulnerable to heatstroke if there’s a sudden increase in temperature, like a heat wave, and their body isn’t acclimated to the heat. That’s why football players sometimes develop heatstroke when they start training in the summer, says Kenney; they aren’t accustomed to working out in high temperatures.

To address heatstroke, people must be cooled down as quickly as possible—preferably by dunking them up to their neck in ice-cold water, says Kenney. It’s also essential that they’re checked out by emergency health care workers or a doctor, who can ensure that their body temperature has cooled down and that their organs aren’t failing.

Extreme heat can fuel mental-health crises

Mental health can be affected by high temperatures. One 2018 study found that higher suicide rates are associated with temperature rises. Nature Climate Change found that for every 1° C increase in the monthly average temperature in the U.S., suicide death rates increased by 0.7%. Researchers speculate that extreme temperatures can cause changes in the mental state.

It is possible that heat can also increase emergency-room visits to treat mental-health crisis. According to a study, published in JAMA Psychiatry In 2022, researchers assessed 3.5 million visits to emergency departments. They found that warmer temperatures increase the likelihood of ER visits for mental-health conditions such as substance abuse disorder and schizophrenia. Amruta nori-sarma, assistant professor at Boston University School of Public Health, and first author of this study says the results likely underestimate the severity of temperature’s effect on mental health. This is because only those with Medicare Advantage or commercial health insurance were included in the analysis. The study also didn’t capture mental-health crises that didn’t involve hospitalization.

Although more research is required to explain why extreme heat causes mental problems, Nori-Sarma thinks poor sleep is one reason. “We know that people struggle to sleep well when it’s very hot outside,” she says. “And we also similarly know that people who have disrupted sleep patterns may experience exacerbations in their existing mental health.”

Heat is bad news for your heart

High temperatures can be more dangerous for people with a range of preexisting health conditions—from Type 2 diabetes to COPD—compared to the general population. High temperatures are especially dangerous for people with heart conditions. They can cause strain to the heart, which could lead to heart attacks. “When our body temperature starts to rise, one of the things that happens is that our heart rate goes up, and our heart pumps harder to try to pump blood flow to the skin to get rid of that heat,” Kenney explains. According to the EPA, about 25% of all heat-related deaths result from a mix of heat and cardiovascular disease.

For people with COPD and asthma, rising temperatures can make breathing more difficult. Air pollution and allergens like pollen—two outdoor conditions that typically accompany high heat—often make this worse.

Kidney problems can be caused by dehydration. The kidneys lose more urine when the body heats up. Chronic dehydration over time can cause kidney failure.

New threats emerge as extreme heat is becoming more frequent due to climate change. Nori Sarma said that multiple extreme events occur more often at once, such as a heat wave occurring in conjunction with a hurricane or drought. Extreme heat is also threatening places where high temperatures haven’t been much of a concern before—like the Pacific Northwest—and those regions may not be equipped with tools like air conditioning.

To reduce risk, says Nori-Sarma, regions should develop “heat adaptation plans” that include resources, like cooling centers, targeted to vulnerable communities.

She says that people living in communities need each other. “It’s really important to make sure that neighbors are checking in on neighbors, and friends are checking in on friends, because that can be one of the best ways to make sure that people are okay during these extreme heat periods,” she says.

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