How to Stay Safe During a Heat Wave

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.)

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. 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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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.

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.)

Here’s what to look for and what to do:

Heat cramps: These painful muscle cramps are often a result of a lot of strenuous activity in the heat. Drinking juice or a sports drink to replenish lost fluid and salt, and resting for a few hours, can help.

Heat exhaustion: Signs of heat exhaustion include feeling tired, weak, or dizzy; sweating heavily; nausea and vomiting; and pale skin. If you notice any of these symptoms, stop what you’re doing, rest, hydrate, and try to cool your body down by getting into air conditioning if you can, or taking a cool bath or shower. If left untreated, heat exhaustion can progress to heatstroke, according to the CDC.

Heatstroke: This condition, which can be fatal, occurs when your body’s mechanism for cooling itself becomes overwhelmed and your temperature rises to 104° F or higher. Signs include confusion or an altered mental state, nausea, red and hot skin, being unable to sweat, a throbbing headache, and/or fainting.

If you suspect that you (or someone else) are suffering from heatstroke, call 911 immediately and begin to try and cool down. Sports teams may keep a tub of ice water on hand for you to submerge parts of your body. Other options include spraying yourself (or someone else) with a garden hose, getting into a cool shower, or sponging down with cool water.

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.