How to stay safe during extreme heat

Scorching temperatures and high humidity—especially together—can pose serious health risks

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Extreme heat can be a killer. In fact, according to the Centers for Disease Control and Prevention, more than 600 people die each year in the U.S. due to extreme heat, often from heatstroke, which occurs when the body’s temperature reaches 104° F or higher.

But often people don’t realize how dangerous extreme heat can be. “It doesn’t come in toppling down trees or damaging homes,” says Michelle Hawkins, Ph.D., chief of the National Weather Service’s Severe, Fire, Public, and Winter Weather Services Branch. “It’s not the type of thing you can see coming at you, but it’s still very deadly and very dangerous.”

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Average temperatures have been rising in recent years—June 2019 was the hottest June ever recorded worldwide—and stretches of abnormal heat seem to be more common these days. The year 2020, according to the National Oceanic and Atmospheric Administration, was the world’s second-hottest ever recorded. Over the next few days and weeks, several western states in the U.S. are facing warnings of extreme heat waves.

A major report from the federal government’s U.S. Global Change Research Program found that heat waves, or six consecutive days of extremely high temperatures, have been increasing in frequency since the 1960s. And they’re expected to continue being more frequent and more intense.

The heat can affect anyone, but older adults, young children, and people with chronic illnesses are most at risk for serious problems. Simple precautions can help keep you safe. Here’s what experts say are the most important safety steps to take during extreme heat.

Check the heat and humidity

There’s no temperature that’s considered the threshold for danger. That’s in part because humidity also needs to be considered: The more humid the air, the longer it takes for sweat to evaporate, and it’s the evaporation process that helps the body cool down.

(In fact, the heat index—a term you might hear in a weather report—is a measure of how hot it feels outside when factoring in humidity and temperature.)

In addition, people who live in warmer climates are acclimated to higher temperatures than those in colder regions, Hawkins says. So what’s considered normal in those areas might be unusually hot in another.

To get heat and humidity information and forecasts for your area, check your local news or go to the National Weather Service’s website and type in your ZIP code.

When you do, you might hear or read about one or more kinds of temperature cautions. A heat advisory signals that a high heat index is forecast for the next one to two days based on your area’s usual climate, and an excessive heat warning means that high heat index will linger for two days or longer, according to Hawkins. (A heat advisory is triggered at a lower heat index than an excessive heat warning.) A heat watch means excessive heat is likely to occur in the area within a few days.

Take steps to stay cool

If your area is experiencing extreme heat, stay in air-conditioned spaces as much as possible, especially during the warmest parts of the day, typically 10 a.m. to 5 p.m. (PDF).

And don’t underestimate how hot it can get indoors without AC. A 2014 study in the journal Science of the Total Environment of 285 low- and middle-income New York City homes found that heat conditions indoors had the potential to reach hazardous levels—which the researchers defined as a heat index of at least 93° F—during heat waves.

That electric fan might not do the trick, either. According to the New York State Department of Health, at indoor temperatures in the high 90s, fans aren’t effective at cooling.

When AC at home isn’t an option, air-conditioned public spaces, such as movie theaters and libraries, can offer a respite. Many are reopening with COVID-19 precautions in place. Check with your local public health department about whether any cooling centers (air-conditioned spaces open to the public) are available in your area; some may still require masks and social distancing.

Inside or out, dress in lightweight, light-colored, breathable clothing. Outdoors, consider adding a wide-brimmed hat, and use sunscreen. Sunburn increases your risk of skin cancer and can hinder your body’s ability to cool itself. Also, be sure to take frequent breaks in an air-conditioned space.

On sultry days, take it easy on outdoor physical activity, too. Leave major outdoor projects until the heat wave breaks, if you can, and do vigorous activity during the coolest parts of the day.

Early morning is best, says Robert McLean, M.D., a past president of the American College of Physicians, because the heat of the day can be slow to dissipate in the evening.