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The major heat exhaustion symptoms and how to avoid heat stroke

Erin Heger,Jason McKnight   

The major heat exhaustion symptoms and how to avoid heat stroke
  • Heat exhaustion symptoms include rapid pulse, nausea, fatigue, and lightheadedness.
  • Heat exhaustion can happen when it's hot and humid, and the body is dehydrated and can't cool itself.

Heat exhaustion is a heat-related illness that happens when the body overheats and cannot cool itself effectively. It's often caused by exposure to extreme heat and humidity. Common symptoms include heavy sweating and rapid pulse.

Heat exhaustion can happen to anyone, but those most at risk include children under four and people over age 65.

Most often, it occurs when people exercise or work outdoors in hot or humid conditions. However, heat exhaustion can also happen indoors, like if you're in a car with the windows rolled up during the summer.

This article discusses the symptoms of heat exhaustion, who's most at risk, and how to treat and prevent it from happening in the future.

Heat exhaustion symptoms

Heat exhaustion is not as serious as heat stroke. However, if you're experiencing the following symptoms, you should seek treatment immediately since heat exhaustion can develop into heat stroke, a more dangerous heat-related illness.

Symptoms of heat exhaustion include:

What causes heat exhaustion?

Heat exhaustion occurs when the body overheats.

Normal body temperature is usually around 98.6°F, but it can vary between 97°F and 99°F. The body can easily overheat when it's dehydrated and in hot, humid environments.

Exerting yourself under these conditions, like exercising, can accelerate the process.

"Your body temperature can increase about a degree for every five minutes of exercise you're doing," says Joshua Scott, MD, primary care sports medicine physician at Cedars-Sinai Kerlan-Jobe Institute.

Sweat is the main way your body cools itself down. But in humid environments, sweat doesn't evaporate as quickly, which can cause you to overheat.

Add high temperatures and exercise to the mix, and you can easily overheat before you know it.

Quick tip: If you have to exercise outside during high temperatures, try to stick to early morning or evening hours when the temperature is lower.

Heat exhaustion treatment

If you're experiencing symptoms of heat exhaustion, it's important to cool yourself down immediately. Try the following treatments:

  • Get out of the heat. Seek shade or get indoors — and preferably in air conditioning — if you can.
  • Hydrate. Sweating cools you down, but it causes you to lose fluids and electrolytes, which are minerals that help keep you hydrated. To treat heat exhaustion, you need to replenish those fluids by drinking water or a sports drink like Gatorade for electrolytes.
  • Use cool water. Help to bring your body temperature down by taking a cool bath or shower, spraying yourself with a garden hose, or by putting wet, cool cloths on your body.
  • Loosen your clothing. Remove any tight or unnecessary clothing if you notice symptoms of heat exhaustion. Multiple layers can trap heat and make it harder for your body to cool itself — light fabrics and loose clothing are always best when it's hot.

When to see a doctor for heat exhaustion

If heat exhaustion symptoms don't improve within an hour of onset or they get worse, you need to seek immediate medical attention.

These more severe symptoms can be a sign that heat exhaustion has progressed to heat stroke, a more dangerous heat-related illness that can be fatal.

Quick tip: Learn more about the difference between heat exhaustion and heat stroke.

Who's most at risk for heat exhaustion?

Heat exhaustion can happen to anyone, but those most at risk include children under four and people over age 65.

That's because the central nervous system isn't fully developed or has lost its ability to regulate temperature as well as most adults, Scott says.

"We know that we become more efficient at cooling ourselves the more we exercise," Scott says. "So going out and exercising for the first time in five or six months can actually predispose you to heat illness."

Some medications, like antihistamines used to treat allergies or diuretics used to treat high blood pressure, may also affect your body's ability to sweat effectively or stay hydrated and can predispose you to heat exhaustion, Scott says.

Quick tip: Talk with your doctor if you're worried that your medication may be causing heavy sweating, rapid pulse, lightheadedness, or nausea during high temperatures.

How to prevent heat exhaustion

If you're going to be exercising or working outside in the heat, here are three of the best ways to protect yourself:

  • Avoid the hottest part of the day
  • Take frequent breaks when exercising or working in the heat
  • Stay hydrated

Overall, you should be consuming about 100 fluid ounces of liquid a day, even if you don't feel thirsty. You usually don't feel thirsty until you're already dehydrated, Scott says, so it's important to drink water throughout the day, and especially when you're working out.

"Dehydration can start to reduce muscle strength which can then reduce your body's ability to thermoregulate itself," Scott says. "So the problems start long before you get thirsty."

Quick tip: If you're frequently active outdoors, consider wearing a "camel pack," a backpack with a drinking hose that contains a bladder that you can fill with water.

Insider's takeaway

Heat exhaustion symptoms can include a rapid heart rate, difficulty concentrating, tiredness, fainting, nausea, cramps, and excessive sweating. Heat exhaustion is not as serious as heat stroke, but it can be dangerous, especially for children under four and adults in their sixties.

It occurs when the body is overheated, dehydrated, and cannot properly cool itself. To prevent heat exhaustion, stay hydrated and avoid exerting yourself during the hottest part of the day.

If you or someone you know is suffering from heat exhaustion, try to cool down with air conditioning, a fan, cold water, or damp cloths.


How long do heat exhaustion symptoms last?

Symptoms may last for up to 30 minutes. However, if the body is unable to be cooled down, it can lead to heat stroke and cause permanent damage or death.

What is the most serious symptom of heat exhaustion?

A high temperature and fainting may be considered two of the most serious symptoms of heat exhaustion.

What are the first signs of heat exhaustion?

The first signs may include profuse sweating, dizziness, weakness and headache.

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