How to Stay Safe During a Heat Wave

Scorching temperatures and high humidity—especially together—can pose serious health risks. Here's how to protect yourself.

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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.”

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.)

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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.

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Stay Well-Hydrated

Usually, letting your thirst to tell you when to drink is a good strategy for staying hydrated. But during an extreme heat event, the CDC advises upping your water intake.

There’s no recommended amount, but make sure you’re sipping regularly, even if you don’t feel thirsty. (If your doctor has told you to restrict fluid intake for medical reasons, ask how you should stay hydrated during extreme heat.)

Water is your best bet for hydrating. Most people don’t need to drink sports drinks, which may contain a lot of added sugars. And avoid dehydrating alcoholic beverages. You can also get water through food, including a variety of fruits and vegetables.

During a heat wave, consider bringing water with you wherever you go, McLean says. That can help you avoid getting stuck in a situation where you’re without it, such as having your car break down on a hot road.

If you notice signs of dehydration, including increased thirst, dry mouth and tongue, restlessness or irritability, decreased urine, or skin slow to move back into place when pinched, drink more fluids right away. If you haven’t urinated in several hours or you’re producing very dark urine, contact a doctor.

Keep an Eye on Those at Higher Risk

Certain groups of people are more prone to heat-related problems. They include older adults and young children, whose bodies aren’t as adept at regulating their temperature, and people with certain chronic medical conditions, including diabetes and cardiovascular disease.

Those who have asthma or chronic obstructive pulmonary disease might experience more breathing problems in the extreme heat, McLean says, and should watch the forecast for air-quality advisories along with extreme heat events.

Certain medications, including diuretics, can also hike the risk of heat-related illnesses.

If you have older relatives or neighbors, call or stop by to check on them frequently during a heat wave. And never leave an infant or child alone in a hot car, even for a few minutes. (The same goes for pets.) If you have a child in the back seat, keep a visual reminder of his or her presence in the front seat, such as a diaper bag or jacket. (Read “Research Shows That Anyone Could Forget Kids in Hot Cars” for more tips.)

Best Window Air Conditioners from CR's Tests

When the heat rises, you’ll appreciate the cooling power of a window air conditioner. Even if you have central AC, there may be places in your house that aren’t getting the full benefit and need a little help. Here are the top-performing small, medium, and large window ACs from our tests.

Catherine Roberts

As a science journalist, my goal is to empower consumers to make informed decisions about health products, practices, and treatments. I aim to investigate what works, what doesn't, and what may be causing actual harm when it comes to people's health. As a civilian, my passions include science fiction, running, Queens, and my cat. Follow me on Twitter: @catharob