The first big heat wave of 2025 has arrived, coinciding with the official .
More than 40 million people in the U.S. were under heat alerts Friday, according to the National Weather Service. Temperatures in the Midwest are expected to crest well into the 90s Fahrenheit (30s Celsius) this weekend. Triple-digit highs could pop up in New York, Philadelphia, Washington and Denver. The peak will likely hit the East Coast early next week.
Meanwhile, British health officials are also issuing heat warnings for the .
Climate change has been and the problem isn't going away any time soon. An increasingly hot planet 鈥� due largely to burning fossil fuels such as coal, oil and natural gas 鈥� means .
Heat doesn't just mean canceled . It also poses a health risk, especially for children, older people and those with certain health conditions.
So here are some tips to stay safe.
When does heat become dangerous?
The answer depends on more than the temperature. The most detailed measurement is called the wet bulb globe temperature (WBGT), which includes temperature, humidity, cloud cover and wind. The heat index, which measures temperature and humidity, is less descriptive but easier to find on weather apps. Both explain why a shaded soccer field on a 90 degree F day (32 degree C) in arid Phoenix may be less risky than an exposed park on an 80 degree F (27 degree C) day in soupy Little Rock.
Just based on heat index, NOAA that calculates how dangerous prolonged exposure can be. For example, a day where temperatures reach 96 degree F (36 degrees C) and 45% humidity would fall into the 鈥渄anger鈥� category for prolonged exposure or strenuous activity.
The WBGT threshold isn't exact, but suggests that even some young, healthy people can't endure hours of exposure to high heat and humidity.
How to cool down
Overnight lows can be a particularly dangerous part of a heat wave, said Ashley Ward, director of the Heat Policy Innovation Hub at Duke University.
鈥淵our body needs a reprieve,鈥� she said. 鈥淵ou don't get that overnight, we start the next day at a deficit.鈥� Heat can worsen labor productivity and lead to more visits to the emergency room.
鈥淲hen we have overnight temperatures that don't drop below 75 degrees" F (24 degrees C), she said, 鈥淵ou start to see some pretty extraordinary outcomes with respect to heat illness and heat stroke, and even mortality.鈥�
Ward's answer: Find air conditioning. That might be at home, but she said census data overcounts how many people have access.
If you can't afford to cool the whole house, Ward said, create a 鈥渃ool corner" and sleep there, so your body is prepared to tackle the next day.
Evaporative or 鈥渟wamp鈥� coolers can help in dry heat, but they increase humidity and can make it more difficult to cool down. In humid places, just use a fan.
If you don't have air conditioning, find public places that do, including movie theaters, malls and libraries. Some communities set up cooling centers.
Depending on where you live, the Low-Income Home Energy Assistance Program can help you buy a window air conditioning unit, . Some local nonprofits and civic organizations can also if cost is a burden.
Know your rights if you work outside
Knowing what workplace protections you have is important. But there are no federal heat rules to protect workers in the United States.
Some states have them, including Washington, Oregon, California, Nevada, Colorado, Minnesota and Maryland, according to Other states don't have any.
If your state has work rules, try to learn them 鈥� though there are still challenges to ensuring regulations are actually enforced, said Bharat Venkat, director of the University of California, Los Angeles Heat Lab.
He notes that sometimes shaded areas are too far for workers to take breaks without losing wages, or that management can make it impossible for workers to advocate for themselves. 鈥淢ost workers don鈥檛 actually have control over their time or control over where they work," he said.
Within those constraints, finding ways to stay hydrated and lower your body temperature are paramount. You can do this by drinking lots of fluids, wetting clothing or putting cold water or a cold rag on your hands, feet, armpits and neck. A portable handheld fan or a cooling vest can also help.
If you're exercising, avoid the hottest times of day and bring more water than you think you need.
Knowing heat illness symptoms
Heat illness symptoms can vary by person, Venkat said. Medications or underlying conditions can also make it harder to regulate body temperature or notice you're getting too hot.
Early include heavy sweating, muscle cramps and headache. That's when you stop what you're doing and cool yourself off 鈥� for example, by splashing yourself with cold water or finding an air conditioned space.
As heat exhaustion sets in, new symptoms arrive, including faster heart rate and dizziness. Next comes heat stroke, which can include confusion, slurred words and fainting. Ward said that's when to call 911.
鈥淒on鈥檛 be embarrassed to call 911 or go to urgent care when you think you might have overdone it in the heat,鈥� he said.
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Walling reported from Chicago. Wells reported from Cleveland.
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Caleigh Wells And Melina Walling, The Associated Press
