Heat Exhaustion

Heat exhaustion happens when your body overheats and can’t cool itself down. It usually results from physical activity in hot weather. Symptoms include dizziness, confusion and nausea. They usually improve by drinking water and resting in a cool place. Untreated, heat exhaustion can lead to heatstroke, a life-threatening condition.


What is heat exhaustion?

Heat exhaustion happens when your body overheats (gets too hot) and can’t cool itself down. Your body can overheat during exercise or any physical activity, especially in hot, humid weather.

During physical activity, your body loses fluids through sweat. If you don’t replace those fluids by drinking water or other liquids, you can become dehydrated. Dehydration can also put you at risk for heat exhaustion.

Symptoms of heat exhaustion can include dizziness, headache, nausea, muscle cramps and others. Treatment includes removal from the heat, rest and fluids. Untreated, heat exhaustion can lead to heatstroke, which can be a life-threatening condition.


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How common is heat exhaustion?

Heat exhaustion and other types of heat illness (hyperthermia) are more common than you might think. Heat exhaustion from exercise happens more often on hot, humid days. Risk factors of heat exhaustion include:

  • Age: Older people and young children have a higher chance of getting heat exhaustion. People over 65 and children under four can’t regulate their body temperature as easily. They are also more likely to get dehydrated (your body doesn’t get enough fluids).
  • Alcohol use: Dehydration can result from drinking excessive amounts of alcohol. Dehydration increases the risk of heat exhaustion. Alcohol also makes it difficult for you to control your body temperature.
  • Lifestyle: Physical activity in a hot, humid environment puts you at a higher risk of heat illness. The risk increases if you wear heavy clothing or equipment. People who aren’t used to working in hot conditions have a higher chance of heat exhaustion.
  • Medications: Side effects of some prescription drugs include vomiting, diarrhea and dehydration, which can lead to heat exhaustion. Diuretics (water pills) to treat heart failure reduce the amount of fluid in your body and can cause dehydration. Chemotherapy drugs (to treat cancer) and beta blockers (to lower blood pressure and slow the heart rate) can also increase the risk of heat illness.
  • Weight and general health: People who carry extra weight have a higher chance of heat exhaustion. Obesity and certain health conditions (such as diabetes and heart disease) increase the risk.

Symptoms and Causes

What are the symptoms of heat exhaustion?

Symptoms of heat exhaustion may develop slowly or appear suddenly. Before heat exhaustion symptoms appear, you may develop a red rash (heat rash) or heat cramps. These painful muscle cramps can affect any muscle, but they usually happen in the arms or legs.

Heat exhaustion symptoms may include:

  • Dizziness, light-headedness, blurred vision and headache.
  • Fever, usually over 100 degrees Fahrenheit. Normal body temperature is 98 F.
  • Fatigue, weakness or fainting (syncope).
  • Nausea and vomiting.
  • Rapid, shallow breaths.
  • Severe or excessive sweating and cold, clammy (damp) skin.
  • Swollen ankles or swelling in the feet and hands (heat edema).
  • Weak, fast heartbeat and low blood pressure when you stand up (orthostatic hypotension).


What causes heat exhaustion?

Usually, your sweat cools your skin and acts like an air conditioner for your entire body. When you’re active (especially in hot weather), your body works hard to regulate its core temperature. Heat exhaustion happens when your body temperature rises too high and your body can’t cool itself down.

During physical activity, your body loses fluids and electrolytes through sweat. Electrolytes are minerals (such as sodium and potassium) that help your body work the way it should. If your body loses too much fluid and sodium (salt) and you don’t replace them, you become dehydrated. Dehydration can lead to heat exhaustion.

Diagnosis and Tests

How do healthcare providers diagnose heat exhaustion?

Usually, healthcare providers diagnose heat exhaustion with a physical examination. Your provider will examine you, take your temperature and ask about your recent activity. If your provider thinks you may have heatstroke, they may order blood and urine tests.


Management and Treatment

What do I do if I think I have heat exhaustion?

If you or someone you know has signs of heat exhaustion, it’s important to take action right away. You should:

  • Cool down: Get to a cool place as soon as you can. Find a shady spot, take a cool shower or sit in an air-conditioned building. You can also wet a washcloth with cold water and place it on your forehead or the back of your neck.
  • Drink: Take small sips of water or a sports drink with electrolytes. Drink water for about an hour, but don’t drink too much too quickly. Avoid alcohol and caffeinated drinks.
  • Rest: Stop doing all physical activity. Sit or lie down so your body can rest.
  • Seek help if you need it: If symptoms don’t get better after about an hour of rest and fluids, call your healthcare provider. If symptoms worsen, call 911 or go to the Emergency Room.


Can I prevent heat exhaustion?

To prevent heat exhaustion, you should:

  • Avoid overheating: If you’re exercising or doing physical activity in hot weather, wear loose, breathable clothing. Take frequent breaks in the shade or another cool spot. When you’re outside on a sunny day, wear a hat with a brim to protect yourself from the sun.
  • Drink fluids: Stay hydrated by taking sips of water or a sports drink every 30 minutes or so. Don’t wait until you’re thirsty to drink. You can lower your chance of heat exhaustion by making sure your body has the fluid it needs.
  • Know your risk: If you take diuretics or other medications that can lead to dehydration, talk to your provider about taking extra precautions in the heat. If you’ve had heat illness before, you’re more likely to develop heat exhaustion.
  • Stay safe in vehicles: The temperature inside a car can rise to dangerous levels very quickly. Never let kids (or pets) play or wait in a parked car. Even if you leave the windows open, sitting in a car on a warm day can be deadly.
  • Time your activities: On hot days, it’s a good idea to exercise early in the morning or late in the day, when temperatures are lower.

Outlook / Prognosis

What is the outlook for people with heat exhaustion?

Heat exhaustion symptoms usually go away after drinking fluids and resting in a cool place. It’s essential to get to a cool place and replace fluids as soon as possible to prevent serious complications.

Untreated, heatstroke can result from heat exhaustion. Heatstroke is a serious, life-threatening condition. It can cause brain damage, organ failure and death.

Living With

When should I see my healthcare provider about heat exhaustion?

If you or your child has signs of heat exhaustion that don’t get better after about an hour of fluids and rest, you need immediate medical care.

Get help right away if you or someone you know:

  • Cannot drink water or keep fluids down.
  • Develops a fever over 103 degrees Fahrenheit.
  • Has trouble speaking, standing up or walking.
  • Is sweating heavily.
  • Seems confused or loses consciousness.

A note from Cleveland Clinic

Heat exhaustion is a serious type of heat illness. Untreated, it can lead to severe health problems and death. If you or your child has signs of heat exhaustion, it’s essential to rest in a cool place and drink plenty of water. Seek immediate medical care if symptoms don’t get better after about an hour. To prevent heat exhaustion, stay hydrated, especially if you’re exercising in hot weather. Listen to your body if you feel thirsty or weak, and take breaks to let your body rest.

Medically Reviewed

Last reviewed on 03/03/2021.

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