This comes just in time for back-to-school season, and health experts at the Children's Hospital of Philadelphia are warning people to be mindful of the signs of heat exhaustion.
"Not sweating is a big indication that your body is not doing well," said Kate Easby, an athletic trainer at CHOP.
"Your body is supposed to sweat when it gets warm, and that's how it gets rid of heat," she continued. "So when it stops sweating, it can't dissipate the heat and then your heat and core temperature start to rise and that can be a problem."
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She adds that feeling dazed and confused also indicates heat exhaustion.
READ | Heat stroke vs heat exhaustion: What's the difference and what are the symptoms?
Heat stroke vs heat exhaustion: What's the difference and what are the symptoms?
Easby says student-athletes and anyone doing physical activity at gym class should make sure they're hydrated, wear proper clothing like lightweight materials, and make sure they take breaks.
"If you're suspecting that someone has a heat-related issue, the best way to treat that person is to put them in a tub of cold water with ice," she noted.
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Philadelphia public schools have already announced they will dismiss students early on Tuesday and Wednesday because of the heat.
Upper Darby and Camden schools announced similar measures.
As for student-athletes, the Pennsylvania Interscholastic Athletic Association (PIAA) is strict about how many hours students can practice in this type of weather.