What Is Heat Exhaustion?


If your body overheats, you will sweat excessively. Sweat, which contains water and salts, is responsible for the unpleasant symptoms of heat exhaustion due to the loss of these components. It needs to be treated quickly before it can develop into heatstroke. There are also other types of heat-related illnesses including heat rash, heat syncope, and heat cramps. This article will discuss heat exhaustion and provide information on how to treat it.

Causes of heat exhaustion

Heat exhaustion occurs as a result of a loss of water and salts through excessive sweating and dehydration. Sweat is the body’s natural way to cool itself down and also to rid the body of toxins. It's made up of water, minerals, and electrolytes including sodium, chloride, potassium, magnesium, and calcium. These are essential for normal body functioning and so losing too much sweat too quickly can result in heat-related illnesses.

Heat-related illness can occur simply from your body getting too hot from being outside in hot weather for too long but can also occur during exercise or working in a hot environment. 

Signs and symptoms of heat exhaustion

The signs and symptoms of heat exhaustion can begin quite subtly but need to be addressed as soon as possible to prevent heat stroke from developing. 1 The symptoms of heat exhaustion include:

  • Headache
  • Exhaustion
  • Pale, clammy skin
  • Dizziness and lightheadedness
  • Feeling sick and/or vomiting
  • Weakness
  • Mood changes, irritability
  • Decreased urination
  • Thirst
  • Sweating
  • Increased body temperature
  • Muscle cramps
  • Rapid, weak pulse

Management and treatment for heat exhaustion

If somebody is experiencing the symptoms of heat exhaustion, it is very important to cool their core body temperature down immediately. Some simple measures that can be taken to ideally lower their temperature within 30 minutes includes:2

  • Moving to a cool place
  • Elevating the legs slightly and supporting them
  • Drinking cool water or a sports rehydration drink to replace the salts they have lost through sweating. NEVER add regular salt to water for the patient to drink, this will worsen their condition.3 You should not consume alcohol or caffeine-containing drinks whilst recovering from heat exhaustion
  • Removing all clothing that isn’t necessary and loosen any tight clothing
  • Cooling down the skin; you can wrap up ice packs in a light cloth and place these under the armpits and around the neck
  •  Using something as a fan to generate cooler air
  • Sitting in a bath of cool water or take a cool shower if available

These measures usually result in the sufferer feeling better within 30 minutes. Don’t leave them alone whilst they are recovering. If you notice a decline in their symptoms, or if they experience confusion, seizures, or an inability to drink seek medical assistance immediately as their condition could have progressed into heatstroke. 

Risk factors

Anybody can develop heat exhaustion, but there are certain risk factors that make certain groups of people more susceptible. These risks include: 


The CNS (central nervous system) plays a role in maintaining a stable body temperature during periods of extreme heat. In young children and those over 65 years of age, the CNS does not work as optimally as in other ages. These groups of people might also have challenges in remaining adequately hydrated. 

Being suddenly exposed to hot temperatures

Heat exhaustion is more common in people that are not used to high temperatures. A study found that for workers who were used to working in hot temperatures, one session of working in the heat was enough for sodium-conserving mechanisms to be activated within the body. A comparison was made with unacclimatized workers, who require a longer period of exposure (10 days or more) to prepare them to avoid fluid imbalances whilst working in hot conditions.4 This study highlighted the need for food intake and rehydration during shifts for all workers. 

Having an occupation that requires working in hot conditions

Workers that are required to spend a lot of time in hot temperatures can quickly become dehydrated and suffer from heat exhaustion no matter how experienced they are. 

Having a long term health condition

Suffering from a chronic illness makes it more difficult to stay hydrated; you may have difficulty looking after yourself and being able to keep yourself cool by getting cold beverages and moving around to cooler areas, for example. 

People with diabetes sometimes have damage to their blood vessels and nerves which can damage sweat glands, therefore their bodies cannot cool down as quickly. Having high blood sugars also causes more frequent urination which involves the loss of water from the body, making dehydration more likely.5

Those suffering from cardiovascular disease are also more at risk for heat exhaustion. This is because, during hot weather, the body has to work harder to keep its core temperature in optimal range, putting extra strain on your heart, lungs, and kidneys.6



If left untreated, heat exhaustion can develop into heatstroke. Heatstroke is a very serious condition that requires immediate medical attention. The symptoms are similar to that of heat exhaustion but do not resolve. Additional symptoms include:7

  • Altered mental state/behaviour
  • Loss of consciousness 
  • Very high body temperature
  • Hot, dry skin
  • Seizures


‘Rhabdo’ occurs from muscle damage. One way in which muscles can get damaged is by engaging in prolonged physical activity in hot temperatures. When muscle tissue is damaged and dies, it releases large proteins and electrolytes into the blood. These can then damage other organs of the body.8

Symptoms of rhabdomyolysis are: 

  • Muscle cramps and aches
  • Dark urine
  • Feeling weak and tired

Heat syncope

Syncope is another word for fainting. Suddenly being exposed to hot temperatures when you’re not used to it and being dehydrated can result in heat syncope. 

Heat cramps

Heat cramps most often affect workers who are carrying out strenuous activity in high temperatures. Excessive sweating means that the body’s salt and water levels are reduced, resulting in painful muscle cramps.9


How can I prevent heat exhaustion?

There are several steps you can take to prevent heat exhaustion, such as:10

  • During hot weather, it’s important to drink plenty of cool fluids, especially if you’re working in the heat or exercising
  • Wearing light coloured clothing made from thinner materials will help to keep the body cooler
  • Avoid drinking too much alcohol
  • Avoid excessive exercise
  • Aim to stay out of the sun during the hottest parts of the day (11 am-3 pm)
  • Closing curtains and windows if you’re inside during hot weather will keep your building cooler if it’s hotter outside than it is inside

How common is heat exhaustion?

Heat exhaustion is common across a wide range of groups including athletes, hikers, and those whose employment requires them to be exposed to high temperatures. It can also occur in those that are recreationally enjoying hot temperatures and not following simple measures to keep themselves cool and hydrated. 

When should I see a doctor?

If you follow the measures mentioned earlier in this article to cool your body temperature down, you should start feeling better within half an hour. However, if symptoms persist or worsen, you should seek medical attention. 


Heat exhaustion occurs when the body’s core temperature is too high. Excessive sweating causes the loss of fluids and electrolytes which contributes to the unpleasant symptoms. If you think you are suffering from heatstroke, take simple measures immediately such as moving to a cooler area and drinking cold fluids. You should begin to feel better fairly quickly. If heat exhaustion is not acknowledged quickly, it can develop into heat stroke which can be fatal. 

Certain groups are more at risk of heat exhaustion due to their age, occupation, and health status. It’s especially important to look out for these people during periods of hot weather. 

Prevention of heat exhaustion is possible if the body is kept at an optimal temperature and hydration is adequate. 


  1. Heat stress related illness | niosh | cdc [Internet]. 2022 [cited 2023 Jun 2]. Available from: https://www.cdc.gov/niosh/topics/heatstress/heatrelillness.html
  2. Heat exhaustion: First aid [Internet]. Mayo Clinic. [cited 2023 Jun 2]. Available from: https://www.mayoclinic.org/first-aid/first-aid-heat-exhaustion/basics/art-20056651
  3. Heat exhaustion - causes, symptoms & treatment - st john ambulance [Internet]. [cited 2023 Jun 2]. Available from: https://www.sja.org.uk/get-advice/first-aid-advice/effects-of-heat-and-cold/heat-exhaustion/
  4. Bates GP, Miller VS. Sweat rate and sodium loss during work in the heat. J Occup Med Toxicol [Internet]. 2008 Jan 29 [cited 2023 Jun 2];3:4. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2267797/
  5. CDC. Managing diabetes in the heat [Internet]. Centers for Disease Control and Prevention. 2022 [cited 2023 Jun 2]. Available from: https://www.cdc.gov/diabetes/library/features/manage-diabetes-heat.html
  6. Hot weather and your heart [Internet]. British Heart Foundation. [cited 2023 Jun 2]. Available from: https://www.bhf.org.uk/informationsupport/support/practical-support/weather-and-your-heart
  7. Heat stress related illness | niosh | cdc [Internet]. 2022 [cited 2023 Jun 2]. Available from: https://www.cdc.gov/niosh/topics/heatstress/heatrelillness.html
  8. Symptoms: rhabdomyolysis | niosh | cdc [Internet]. 2023 [cited 2023 Jun 2]. Available from: https://www.cdc.gov/niosh/topics/rhabdo/symptoms.html
  9. Heat stress related illness | niosh | cdc [Internet]. 2022 [cited 2023 Jun 2]. Available from: https://www.cdc.gov/niosh/topics/heatstress/heatrelillness.html
  10. Heat exhaustion and heatstroke [Internet]. nhs.uk. 2017 [cited 2023 Jun 2]. Available from: https://www.nhs.uk/conditions/heat-exhaustion-heatstroke/
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Jessica Gibson

Bachelor of Science- BSc(Hons)- Health Sciences- The Open University

Jessica is a Health Sciences graduate with a passion for both Science and English and is delighted to have found a way to combine the two. She is a motivated and enthusiastic writer determined to make scientific information more widely accessible.
Jessica is especially interested in infectious diseases, neurodegenerative diseases, the impact of trauma on physical health, health equity and the health of children residing in developing nations.

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