Here's how to know when you need to cool off.

Heat-related deaths and illnesses are entirely preventable—and yet, extreme heat causes 618 deaths in the US each year, according to the Centers of Disease Control and Prevention. Generally speaking, heat-related illnesses occur when the body isn't able to properly cool itself (normally, the body cools itself automatically through sweat, but in settings of extreme heat, that's not always enough, per the CDC). 

Heat stroke and heat exhaustion are the two main heat-related illnesses that can lead to more severe issues. Heat stroke, which is the most serious heat-related illness, happens when the body becomes unable to control its own temperature after the body's temperature rises and its ability to cool off through sweating fails. The CDC says that during heat stroke, body temperature can rise to as high as 106 degrees Fahrenheit in as little as 10 minutes, and can cause death or permanent disability if left untreated. Heat exhaustion, on the other hand, is less severe than heat exhaustion and can develop after several day of exposure to hot temperatures and inadequate fluid intake.

While anyone can fall victim to heat exhaustion, it's most common in older adults and those with high blood pressure. People regularly exercising outside in the heat are also prone to heat exhaustion, says Samantha Smith, MD, a Yale Medicine sports medicine doctor and assistant professor of clinical orthopedics and rehabilitation at Yale School of Medicine. "We increase our heat production up to 20 fold when we exercise," she says. 

Luckily, heat exhaustion has some key signs and symptoms that can make it easier to diagnose if you or someone you're with starts feeling unwell in the heat. Those symptoms include:

  • Heavy sweating
  • Paleness
  • Muscle cramps
  • Tiredness
  • Weakness
  • Dizziness
  • Headache
  • Nausea or vomiting
  • Fainting

Left untreated, heat exhaustion can progress into the more serious heat stroke, so if you start to experience any heat exhaustion symptoms, Kirsten Bechtel, MD, a Yale Medicine emergency medicine doctor and associate professor at Yale School of Medicine, suggests doing a number of things to cool your body down, starting with resting in a cool place, like an air-conditioned room. “Lie on your back and raise up your legs so they are higher than the level of your heart,” she says. If possible, take a cool shower, soak in a cool bath, or put towels soaked in cool water on your skin. Loosen clothing so air can circulate around your skin, if a cool bath or shower isn't possible.

Hydration is also key. “Drink plenty of cool fluids,” says Dr. Bechtel. “Stick to water or sports drinks. Avoid caffeinated or alcoholic beverages as they can be dehydrating.” If taking those steps don't help you feel better, your symptoms last longer than an hour, or those symptoms begin to worsen, it's important to seek medical care immediately.

Luckily, there are also ways to prevent heat exhaustion, like wearing lightweight clothing while outside in the heat, per the CDC. And if you're planning on exercising in a hot environment, make sure to give your body a chance to adapt to the temperature. "Healthy people can adapt to exercising and living in hot environments, but this takes some time, usually 5 days or more," says Dr. Smith.

It's also important to pay attention to the weather conditions, including the heat index. “Try to exercise in the cooler morning or evening hours,” she suggests, and make sure to stay hydrated before exercise and replace what you sweat during and after exercise. Overall, Dr. Smith says to "pay attention to your body, even more when conditions are very hot and humid."

To get our top stories delivered to your inbox, sign up for the Healthy Living newsletter