The record-high temperatures that have affected swaths of North America, including the Pacific Northwest, where an alarming and historic heat wave has caused hundreds of deaths, have signaled to health and environmental experts that the public needs to know how to deal with extremely hot weather.

“As we move forward into essentially a hotter planet, we need to really rethink heat as a risk,” said Sabrina McCormick, an associate professor of environmental and occupational health at George Washington University. “Everyone is vulnerable, and these exposures can creep up and unexpectedly affect you, so you need to really keep an eye on it.”

Below we’ve compiled answers to frequently asked questions about extreme heat, as well as tips from experts for how to best protect yourself and others this summer and beyond.

Frequently Asked Questions

  • What is extreme heat?
  • What heat-related conditions should I watch out for?
  • How can I stay safe in extreme heat?
  • Who is at increased risk of being affected by heat?
  • If I feel sick or notice someone who isn’t well, what should I do?

What is extreme heat?

The Centers for Disease Control and Prevention defines extreme heat as “summertime temperatures that are much hotter and/or humid than average” for a particular area. (Humidity and muggy conditions can make it feel hotter than it actually is, the CDC notes.) What would be considered “extreme” in Arizona, for instance, wouldn’t be the same in Oregon.

When someone who is not acclimated or is more vulnerable to higher temperatures is exposed to extreme heat, their body’s “ability to thermoregulate, or control its own internal temperature, begins to break down,” said Steve Mitchell, medical director of the emergency department at Harborview Medical Center in Seattle.

Grant Lipman, a clinical professor of emergency medicine at Stanford University, describes it this way: “Imagine frying an egg. That’s what’s happening in your body at these 106, 107 core temperatures. You have all these proteins and enzymes in your body that are basically being fried and you’re losing cells and you’re having this multi-organ dysfunction.”

What heat-related conditions should I watch out for?

Health risks associated with heat exposure exist on a spectrum ranging from milder conditions such as heat cramps to heat strokes, which can be fatal. It’s important, experts say, to familiarize yourself with the symptoms of heat-related illnesses so you can head off potential problems.

Mild dehydration and heat cramps — muscle pain or spasms — may be early signs that your body is not reacting well to the environment, said Matthew Levy, an associate professor of emergency medicine at Johns Hopkins University School of Medicine.

Heat exhaustion symptoms are more worrisome. These can include heavy sweating, elevated heart rate, nausea and vomiting, headaches, dizziness, fatigue and generally feeling unwell. Some people who are experiencing heat exhaustion might also faint. “This is where things are getting dangerous fast,” Levy said.

If heat exhaustion is left untreated, you may progress to heat stroke, which means the body’s core temperature has reached the point where cellular damage may start to occur, said Lipman, a wilderness medicine expert and the founder of Global Outdoor Emergency Support (GOES), an app designed to help people with outdoor health and emergency medical support.

The key feature of heat stroke is central nervous system dysfunction. “You’re confused, you’re altered, you might have seizures,” he said.

Another sign is lack of sweat. “The dry person who’s not thinking clearly is at big risk and should really rapidly seek help as soon as possible,” Mitchell said.

The best way to deal with heat stroke is to prevent it. “Once you get on that road to heat stroke, it’s actually quite hard to get off,” McCormick said.

How can I stay safe in extreme heat?

Your priority should be keeping yourself cool and hydrated.

Make sure you can access a space with air conditioning. If you can’t, find out in advance what resources — such as designated cooling centers — are available in your community. Then, utilize them, especially during the hottest parts of the day. If you only have a fan, experts recommend misting yourself with a spray bottle of cold water. But, Levy said, that shouldn’t be a substitute for air conditioning, especially in extreme heat conditions.

You could also spend time at indoor public places such as malls or libraries. If you live in an urban area, consider going to a park, which can be “five to 10 degrees lower than being out on the concrete or in a building surrounded by concrete,” McCormick said.

If you have to work outdoors, dress in loose, lightweight, light-colored clothing and protect yourself from the sun with hats, sunglasses and sunscreen. The hotter it is, the more frequently you should be taking breaks. You can also try to stay cool by soaking your head and shirt in water.

Although you should be well-hydrated, you don’t need to guzzle water.

Drinking too much water could cause a potentially fatal condition known as hyponatremia, or when the sodium in your body becomes diluted and levels drop abnormally low. Lipman recommends keeping salty snacks on hand if you’re going to be consuming large amounts of liquids.

Experts also caution against drinking excessive amounts of alcohol or caffeine, both of which can be dehydrating. A good way to know whether you’re adequately hydrated is to pay attention to the color of your urine. “When you do urinate, if it’s really dark yellow, that’s not a good sign,” Mitchell said. “If it’s clear, that’s a very good sign.”

In addition to ensuring you have access to cooler environments and adequate hydration, plan your activities with the weather in mind. If you want to exercise outside, experts suggest choosing less intense workouts and doing them early in the morning or in the evenings.

Who is at increased risk of being affected by heat?

Although anyone can be negatively affected by hotter temperatures if they’re not careful, certain populations are more vulnerable, including the elderly, young children, athletes, people who have chronic medical conditions, pregnant people and those who may be struggling with mental health issues. Heat can also exact a psychological toll on people who don’t have preexisting mental health conditions.

When people become dehydrated, “the electrolytes go out of sync, their brain isn’t being well-perfused, and that means their body isn’t being well-perfused,” said Saul Levin, chief executive and medical director of the American Psychiatric Association. “You’re going to start feeling things that you don’t usually feel, which only then increases the anxiety, increases the depression, increases the feeling of panic.”

If you know anyone who might be at increased risk, experts encourage regularly checking in on them during heat waves and making sure they’re equipped to stay safe. This may mean inviting an elderly relative to stay with you, helping someone get to a community cooling center, or dropping by people’s homes to see whether their air conditioners are working or to bring them cold drinks.

It’s also important to stop and help strangers in need. “Don’t ignore someone and just keep walking,” Levin said. “Humanity is taking care of each other in those sort of situations.” This can be as simple as providing someone with water or helping them find a place to cool down.

Parents, experts say, need to pay particular attention to young children, who should never be left in cars on hot days, even if the windows are open.

And it’s not just humans who experience the toll of heat; pets are at risk, too. If it’s too hot for you, it’s too hot for your pet. Beyond making sure your animals can stay cool and hydrated and watching for signs of overheating, avoid unprotected walks on hot pavement or asphalt, which can cause burns to paw pads.

If I feel sick or notice someone who isn’t well, what should I do?

“Listening to your body is just remarkably important,” Mitchell said. If you notice any symptoms of heat-related illnesses, get into a cooler environment — preferably some place with air conditioning — as quickly as possible. Do whatever you can to lower your body’s core temperature, including taking off clothing and wetting your skin with cold water. Hydrate with cold fluids, such as water or electrolyte drinks.

For more severe problems caused by heat or if you think someone is having a heat stroke, seek medical help immediately.

While waiting for assistance to arrive, it’s critical to take action. Get the person out of the heat and either into air conditioning or shade. The fastest way to cool someone down in an urgent situation is cold-water immersion — “the colder, the better,” Lipman said. If that’s not a possibility, pour cold water on a person’s head and clothing.

No one suffering a heat-related condition should return to the activity they were doing until they are completely back to normal. “If you ignore these early warning signals and try to work through or play through, that’s when you’re going to get into trouble,” Lipman said.

Though many people are eager to get on with their lives again, he added, you need to keep in mind that you can so easily “get yourself in trouble and you can get ill and you can die,” he said. “It’s a tragedy and totally preventable.”