With record temperatures ravaging regions from Europe to the US, health officials are warning locals and travellers alike to heed the heat and take precautions against heat illness.

So, what are the signs, and what are the best ways to mitigate a situation that is only expected to get worse as the world increasingly faces prolonged and unprecedented summer temperatures?

From heavy sweating and dizziness to muscle spasms and even vomiting, experts say heat exhaustion and heat stroke are likely to become more common, and knowing the warning signs is critical to knowing when to quit and get out of the sun into a cooler place.

Heat stroke

Heat stroke is the most serious heat-related illness and happens when the body loses its ability to sweat.

The skin gets hot and red, and the pulse quickens as the person’s body temperature climbs to 103 F (39 C) or higher. Headaches set in, along with nausea, confusion, and even fainting.

Jon Femling, an emergency medicine physician and scientist at the University of New Mexico, said the body tries to compensate by pumping blood to the skin as a way to cool off. And the more a person breathes, the more they lose fluids, becoming increasingly dehydrated.

Important electrolytes like sodium and potassium also can be lost when sweating.

“So, one of the first things that happens is, your muscles start to feel tired as your body starts to shunt away,” he said. “And then you can start to have organ damage where your kidneys don’t work, your spleen, your liver. If things get really bad, then you start to not be perfusing your brain the same way.”

Experts say it’s also important to recognize the signs of heat stroke in others, as people may not realize the danger they’re in because of an altered mental state that may involve confusion.

In the case of heat stroke, experts suggest calling 911 and trying to lower the person’s body temperature with cool, wet cloths or a cool bath.

Heat exhaustion

With heat exhaustion, the body can become cold and clammy. Other signs include heavy sweating, nausea, muscle cramps, weakness, and dizziness.

Older people, children and those with health conditions can face greater risks when the temperatures are high.

During extreme heat events, one of the most common ways people can die is from cardiovascular collapse, experts said, because of the extra energy the heart has to expend to help the body compensate for the hot temperatures.

And it’s not just the heat – humidity can make it more difficult for the body to produce sweat as a way to cool off.

Finding relief

In general, health officials say staying indoors, seeking air-conditioned buildings, and drinking more water than usual can stave off heat-related illnesses. Caffeine and alcohol are no-nos. Eating smaller meals more often throughout the day can help.

And for those starting to feel the effects, experts say the best thing to do is to move to a cool place, loosen clothing, and sip some water.

“In any sunny hot area,” says Jenni Vanos, an associated professor at Arizona State University, “shade is a really critical factor to be able to reduce that overall heat load of the human body.”