How Humidity Makes Beating the Heat Harder for Older Adults

Extreme heat can be tough as we age, but humidity adds another barrier to staying cool

Kristen Fischer,

AARP

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Published June 20, 2025

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This summer is expected to be a scorcher in the U.S., with temperatures spiking above average across much of the country. Older adults face higher health risks from heat, but many may not be aware of the added punch that humidity can have on their well-being.

“Heat and humidity often go hand in hand,” Deborah Carr, director of the Center of Innovation in Social Science at Boston University, who has studied heat’s impact on health, told AARP. And, she says, “humidity does have specific impacts on our body.”

Here’s a look at how hot and humid days can affect the health of older adults — and what you can do to lower your risks when the temperatures soar and the humidity levels start to climb.

The science of sweat and aging

In the heat, your body stays cool using two mechanisms, says Daniel J. Vecellio, an assistant professor at the University of Nebraska at Omaha who studies the impacts of heat and humidity on human health. You pump more blood to protect your internal organs, causing the heat to move toward the surface of your skin. You also sweat, so long as you have enough water and working glands to release the sweat.

Is it just me, or is it getting more humid?

Scientists aren’t sure if it’s getting more humid globally — reports tend to differ, Vecellio says — though they know average temperatures are climbing.

Researchers have coined the term “moist heat stress” to define the combination of humidity and extreme heat. According to the authors of a report in Environmental Health Perspectives, increasing temperatures and humidity have created a compound risk for humans.

When it’s dry, the evaporation of that sweat helps to keep you cool. But when it’s hot and humid, the sweat you produce to cool your body down doesn’t evaporate easily since there’s already so much moisture in the air. This creates a barrier and you don’t feel the cooling effect of sweating, Vecellio says.

“Just because you produce the sweat doesn’t mean you get any cooling occurring,” Vecellio says. “It’s the evaporation of sweat off our bodies that allows us to physiologically cool ourselves down.”

Here’s what makes humidity so hard for older individuals: As you age, you don’t sweat as much, plus you have fewer active sweat glands. In fact, thermoregulatory sweating can decline by up to 25 percent in those over age 60, a 2023 study in Environmental Health Perspectives reports. (Some people can also sweat too much, which causes other complications, as noted below.)

The temperature at which we start to lose the ability to regulate our body temperature, paving the way for heat-related complications, is lower than previously thought, Vecellio found in his 2022 study. Instead of the threshold being 95 degrees at 100 percent humidity or 115 degrees at 50 percent humidity, researchers found it was 87 degrees at 100 percent humidity and nearly 104 degrees at 50 percent humidity. This was in young, healthy people. Knowing this could help people take better care of themselves in high heat, his team wrote.

Though many population-level studies help us examine weather trends, they don’t tell us how an individual will do in heat and humidity because everyone is different.

“Like all things in health research, extrapolating to ideal recommendations for specific people is much trickier and often should be done in a conversation with a trusted physician,” Sam Silva, an assistant professor of earth sciences, civil and environmental engineering, and population and public health sciences at the University of Southern California, Dornsife, told AARP.

The age factor

“Although humidity is miserable for everyone, it’s worse for older people,” Carr says. The diminished capacity to cool down makes them more vulnerable to dehydration, heat stroke, dizziness, fatigue, confusion and delirium, she adds.

Older adults who do sweat can also experience problems. Sweating too much depletes fluid levels of water and chemicals needed for proper function. That can lead to dehydration, fainting, heat exhaustion and heat stroke.

Further complicating matters, common prescription medications taken by many older adults can make individuals more sensitive to humidity, Carr says. Anticholinergics, used to treat chronic obstructive pulmonary disease (COPD), further reduce our capacity to sweat, which is especially problematic on very humid days. Dehydration is a side effect of beta blockers and diuretics, which are used to help control blood pressure, Carr adds.

Humidity can also interrupt your sleep quality as you age. You may feel restless because it’s harder to cool down. A bad night of sleep can lead to daytime fatigue, mood changes and weakened immune function, Carr says.

High humidity can make it harder for older adults to recover from rashes or other skin problems like athlete’s foot because humidity encourages fungus and bacteria to thrive, Carr says.

Joint swelling can also be worse in humidity, especially for those with arthritis.

“Humid weather may increase stiffness and reduce mobility, making it more difficult for older people to do their everyday activities,” Carr says.

Existing cardiovascular issues make it harder for older adults to pump blood in response to the heat. This can cause life-threatening complications, Vecellio says. Cardiovascular issues “just enhance your risk to become overheated because your heart is not able to work as well and dissipate that heat away,” he notes.

In fact, most people who die during extreme heat succumb to cardiovascular episodes such as heart attacks or cardiac arrest and not issues like heat stroke, Vecellio says.

Regular exercise can thwart the potential harms of high heat and humidity, though.

“Physical fitness really does do wonders as we age,” says Vecellio, who adds that when it comes to handling heat later in life, it’s especially important to stay healthy in midlife.

One important note: While humidity can certainly make things worse during high-heat days, older adults need to be careful even in dry heat. Although the air is dry enough to evaporate any sweat, you may not sweat enough to get a cooling effect, Vecellio says.

Beating the heat and humidity

If it gets humid, experts say, it’s important to follow traditional heat safety tips, like staying hydrated, to prevent negative health impacts.

But keep in mind that when it’s humid, staying in the shade or running a swamp cooler (a device that cools the air by evaporating water) won’t help much because these cooling methods work better in dry conditions, Silva says.

Use air-conditioning or a dehumidifier when it’s hot and humid, Carr suggests. “If you don’t have or can’t afford air-conditioning, consider staying with a friend or visiting a local cooling center,” she adds.

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Kristen Fischer is a contributing writer at AARP based at the Jersey Shore. She has also written for Health, WebMD, and McKnights and is the author of Zoo Zen: A Yoga Story for Kids.