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10 Warning Signs of Heat Stroke

Heat stroke is sneaky and silent—and it can be fatal. Knowing the causes and the treatment is crucial to protecting you and your loved ones.

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What is heat stroke?

It’s a term you may also hear referred to as “sunstroke,” and it is clinically defined as when your core temperature soars above 104 degrees Fahrenheit, along with central nervous system dysfunction, explains James Winger, MD, associate professor of family medicine at Loyola University Medical Center in Chicago. Also, the signs of heat stroke are different from heat exhaustion—learn how to tell them apart here.

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Two “types” of heat stroke

Heat stroke can happen in two main ways. One is from exertion, when “exercise raises someone’s core body temperature and the systems that usually help the body cool back down don’t work,” says Dr. Winger. For instance, high humidity may impair the body’s ability to cool itself off through perspiration—sweat. A second cause is due to environmental factors like being in a heat wave with no access to air conditioning, for instance.

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Warning sign: Confusion

This is by far one of the biggest signs of heat stroke. It’s actually similar to hypothermia (when the body temperature drops too low): Sufferers may begin to make poor decisions or not respond appropriately when asked a question. One example might be getting lost in a trail race because you can no longer properly navigate, says Dr. Winger. These are some more signs of hypothermia that are easy to miss.

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Warning sign: Not acting “like yourself”

Because your mental capacities are compromised, it’s rare that you’d recognize your own brain blips. But people around you can pick up on it. “It’s best to consider if the person is not behaving appropriately to the situation they’re in—this makes it more likely you’ll flag someone in the earliest stages of illness,” says Dr. Winger.

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Warning sign: Dizziness

Disorientation is physical, too. Dizziness or staggering are also signs of exertional heat stroke, according to the University of Connecticut’s Korey Stringer Institute. Dehydration can mess with your equilibrium, so take time to stop and catch your breath, drink water, and reevaluate your activity game plan, if necessary. Dehydration is just one of the reasons why your head may be spinning

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Warning sign: Nausea

If you’re exercising and dealing with nausea, it could mean that the peanut butter toast you ate before heading out is just not sitting right with you. But if it’s a hot day (and you’re not acclimated to working out in the heat) and nausea hits, be wary of heat stroke. Be especially concerned if you vomit. Dr. Winger says that at organized races, doctors in medical tents will have athletes lie down for a few minutes and, if rest doesn’t help them feel better, the doctors will suspect heat illness.

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Warning sign: Headache

You’ll likely get a headache with heat stroke, and it’s an early warning sign since you’ll get it with heat exhaustion, according to Beaumont Health. But while you may be able to treat heat exhaustion by going indoors and turning up the air-conditioning, taking a cool shower, and drinking rehydrating, with heat stroke you have an emergency that requires a swift call to 911. Headaches can actually indicate any number of serious problems.

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Warning sign: Lack of sweat

It’s hot and you should be sweating buckets; if not, it may be a sign of heat stroke. However, this is more likely in non-exertional heat stroke and doesn’t often occur from exercise. “This is one sign that everyone knows but doesn’t actually happen as much as we think,” says Dr. Winger. If you’re out there running and notice that there’s a layer of dry salt on your body, that’s actually an indication that your body is sweating as it should. The difference is when you’re not exercising but are enduring the heat and your skin stays dry.

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Warning sign: Red skin

Skin that’s red and hot is another indication that your body may be dangerously overheating. Now’s the time to take action to cool off before things progress. Along with watching out for loved ones, your dog can become dangerously overheated too: Watch for these heat stroke signs in furry pals.

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Warning sign: It’s an unseasonably hot day

You’d assume that the end of the summer would be the worst time of year, but when it comes to exercise-induced heat stroke, it’s actually the beginning of the summer season or early fall that can be trouble—should an uncommonly hot day occur. “When your body acclimatizes to hotter weather, you become a more efficient and voluminous sweater, which serves as a big defense against heat illness,” says Dr. Winger. If your body isn’t used to the heat, take frequent breaks, sip water or a sports drink to thirst, and seek out shady routes.

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Warning sign: Passing out

Infants, the elderly, and people with chronic diseases are especially vulnerable to heat stroke, according to the CDC. The Mayo Clinic points out that fainting may be the first sign of heat stroke in these individuals. During a heat wave, keep a watch on people who fall into these groups; call 911 if they should pass out and consider CPR if necessary—brush up on your skills here.

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Warning sign: Heat exhaustion

If you have heat exhaustion, you may be sweating profusely or have a rapid pulse, according to Mayo Clinic. This condition, also caused by the body overheating, can progress to heat stroke if not properly treated. They recommend resting right away and cooling your body down by moving to shade or air conditioning and drinking fluids.

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What to do if you think you have heat stroke

Doctors can’t stress this enough: Call 911. In fact, the US Department of Health & Human Services notes that people with heat stroke should be admitted straight to the ICU. If you are with a victim while waiting for help to arrive, you can fan and sprinkle them with water to help their body cool down. At the hospital, treatment involves cool water immersion or ice packs placed on the groin, neck, and armpits. And keep an eye out for these other 50 summer health dangers you’re probably ignoring.

Jessica Migala
Jessica Migala is a freelance health and fitness writer with more than a decade experience reporting on wellness trends and research. She's contributed to Health, Men's Health, Family Circle, Woman's Day, and O, The Oprah Magazine, among other publications. Jessica lives with her husband and two young sons in the Chicago suburbs.