Heat exhaustion occurs when the body becomes dehydrated and is unable to regulate its internal body temperature.
The condition is not usually considered life-threatening and is treatable with fluids and rest. In this article, we look at the symptoms and treatment of heat exhaustion, as well as how to prevent it.
Normally, the body gets rid of excess internal heat by pumping blood to the surface of the skin and releasing sweat. Warm, moist air absorbs less sweat from the skin and limits the body's ability to cool itself by sweating.
When the body is dehydrated, it lacks water and essential salts called electrolytes, which reduces its ability to sweat.
If a person is unable to cool down by sweating, they may experience heat exhaustion.
Heat exhaustion usually causes a rise in body temperature, even though it can sometimes cause a person to feel cool.
The symptoms of heat exhaustion can be easy to overlook and are similar to those of many other medical conditions.
Common signs of heat exhaustion include:
- weak, rapid pulse
- excessive sweating
- increased internal body temperature
- muscle weakness or cramps
- cold, pale, damp skin, sometimes accompanied by goosebumps
- low blood pressure or light-headedness when standing up or bending over
- irritable or aggressive behavior
- red, flushed face
- rapid, shallow breathing
Symptoms of heat exhaustion in children
The symptoms of heat exhaustion in children are similar to those in adults; they may:
- seem excessively tired
- be unusually thirsty
- have cool, clammy skin
If they are old enough, they might complain of stomach or leg cramps. It is important to treat a child with heat exhaustion immediately.
Heat exhaustion versus heat stroke
Heat exhaustion, if left untreated, can lead to heatstroke.
Unlike heatstroke, which can be life-threatening, heat exhaustion does not cause impaired mental function, confusion, or loss of consciousness.
Cases of heat exhaustion are also distinguished from heatstroke because a person's internal body temperature does not go above 103°F.
Heat stroke is less common than heat exhaustion but more serious; it puts strain on the heart, lungs, kidneys, and liver.
Heat exhaustion is most often caused by a combination of physical exertion and warm weather.
Additional factors known to increase the likelihood of heat exhaustion include:
- high humidity, usually over 60 percent
- liver or kidney conditions
- intense, strenuous physical work
- underlying conditions that increase the chances of dehydration, including diabetes or hyperglycemia
- injuries where a portion of the body is compressed or pinned down by a heavy object, also known as crush injuries
- drug abuse
- heavy or long-term alcohol use
- smoking or tobacco use
- being overweight
- certain medications, especially those that increase the risk of dehydration, including medications for depression, insomnia, allergies, and poor circulation
- high blood pressure
- heart disease
- being under 4 or over 65 years old
On its own, heat exhaustion is not considered a major health concern. If left untreated, however, heat exhaustion can lead to heatstroke and further complications, including brain damage and organ failure.
In rare cases, when heat exhaustion is accompanied by intense exercise or other medical conditions, it may cause a serious health risk.
Potential complications of heat exhaustion include:
- severe kidney injury
- rhabdomyolysis, which can cause kidney failure, tea-colored urine from an increase in the muscle protein myoglobin, irregular heartbeat, muscle pain, and vomiting
- liver failure
- arrhythmias, or a heartbeat that is either too fast or too slow
- delirium or coma
If heat exhaustion is suspected, a person should stop doing exercise or physical activity immediately. A person with heat exhaustion should also drink fluids as soon as possible.
Further tips for treating heat exhaustion include:
- seeking out a cool, shaded area or going indoors
- loosening clothing
- lying flat on the back
- taking a lukewarm or cool shower
- placing a cool, wet cloth on the face and chest
- in severe cases, putting ice packs under each armpit and behind the neck
- drinking 1 liter per hour of drinks that contain electrolytes, such as Gatorade or Gastrolyte
How to rehydrate
Make an at-home oral-rehydration solution by following these steps:
- boil 5 cups (1 liter) of water
- remove from the heat source and stir in 6 teaspoons (tsp) of sugar and ½ tsp of table salt
- cool before drinking
- add natural flavorings in the form of fruit juices, honey, or maple syrup
Some drinks and foods can also act as oral-rehydrating formulas, including:
- gruel (cooked cereal and water)
- rice water or congee
- green coconut water
- fresh fruit juices, ideally orange, pear, or peach
- weak, non-caffeinated tea
- carrot soup
- banana puree mixed with water
In most people, symptoms of heat exhaustion will start to improve within 30 minutes. However, if symptoms do not improve after 30–60 minutes, seek medical attention.
A doctor will treat heat exhaustion with one or two liters of intravenous (IV) fluids and electrolytes.
If fluids and rest do not resolve symptoms, a doctor will perform a blood work-up and other clinical tests to rule out other potential causes.
If heat exhaustion is treated promptly, the individual will be fully recovered within 24-48 hours.
A person can help prevent heat exhaustion by staying hydrated and cool.
Other ways to prevent heat exhaustion include:
- drinking fluids during and after exercise
- avoiding exercising in direct sunlight in warmer months
- avoiding prolonged exposure to hot, humid weather
- wearing loose-fitting clothing when exercising or when in warm weather
- keeping electrolyte beverages or oral-rehydration salt preparations on hand
- avoiding sugary drinks and sodas
- not increasing workload or pace too quickly
- exercising in a well-ventilated area or while using a fan
- seeking air-conditioned, indoor areas when outdoor temperatures are over 90°F
- applying sunscreen with SPF 15 or higher 30 minutes before going outdoors and reapplying often
- in the summer, scheduling strenuous activities during the early morning or evening
- increasing fluid intake when using medications known to increase the risk of heat exhaustion
- keeping hydrated when working in hot, humid environments, such as factories, laundry facilities, and kitchens
- wearing lightweight, light-colored clothing when exercising or working in warm weather
The symptoms of heat exhaustion are meant to warn the body that it is becoming overheated.
Heat cramps, the mildest type of heat-related syndromes, usually occur before heat exhaustion. Treating heat cramps as soon as they occur may prevent heat exhaustion from developing.
Symptoms of heat cramps include:
- heavy or excessive sweating
- muscle pain and cramps
- fatigue or tiredness
Heat cramps can be treated with fluids and rest. A person should also seek shade or an air-conditioned building as soon as possible.