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Overview
What Is Heat Exhaustion?
Heat exhaustion is a heat-related illness that develops when the body cannot cool itself effectively. Excessive heat, sweating, and fluid loss can cause weakness, dizziness, nausea, headache, and other symptoms. People who work or exercise in hot conditions, older adults, young children, pregnant people, and those with certain health conditions are at higher risk. Heat exhaustion can worsen into heat stroke, which is a medical emergency.
Symptoms
Heat Exhaustion Symptoms
- Heavy sweating
- Cool, pale, or clammy skin
- Weakness or unusual tiredness
- Dizziness
- Headache
- Nausea
- Muscle cramps
- Fast, weak pulse
- Thirst
- Fainting
Know the difference
When heat exhaustion may be heat stroke
Confusion, unusual behavior, fainting, seizures, loss of consciousness, or a very high body temperature may indicate heat stroke rather than uncomplicated heat exhaustion. Heat stroke is life-threatening; call emergency services immediately and begin cooling while waiting for help. Do not give fluids to someone who is confused, unconscious, vomiting repeatedly, or unable to swallow safely.
Causes
What Causes Heat Exhaustion?
Heat exhaustion occurs when heat gain and sweating cause the body to lose water and electrolytes faster than they can be replaced. As fluid and salt levels fall, the body has more difficulty maintaining blood flow, sweating effectively, and regulating temperature. This can happen during excessive heat, especially when exertion adds to the body’s heat load.
- Spending a long time outdoors in hot weather can overwhelm the body’s cooling system.
- Strenuous exercise or physical work increases internal heat and sweating.
- Humid conditions slow the evaporation of sweat and make cooling less effective.
- Not drinking enough fluids increases the risk of dehydration and heat illness.
- Heavy, tight, or nonbreathable clothing can trap heat and moisture.
- Lack of heat acclimatization can make it harder to tolerate a sudden increase in temperature or activity.
Risk Factors
Heat Exhaustion Risk Factors
SITUATIONAL OR MODIFIABLE FACTORS
Risk increases with prolonged sun or heat exposure, strenuous activity, inadequate fluid intake, alcohol use, heavy clothing, limited access to shade or air conditioning, and sudden exposure to hot weather. Taking cooling breaks, drinking regularly, adjusting activity, and acclimatizing gradually can reduce some of these risks.
HEALTH AND VULNERABILITY FACTORS
Older adults, infants and young children, pregnant people, and people with heart, kidney, lung, or other chronic conditions may be more vulnerable. Some medications can affect sweating, hydration, blood pressure, or heat tolerance, and people who are dehydrated or not acclimatized may become ill more quickly.
Complications
Heat Exhaustion Complications
Potential complication
Progression to heat stroke
Heat exhaustion can progress to heat stroke, although this does not happen in every case. Confusion, altered behavior, fainting, seizures, loss of consciousness, or a very high body temperature are warning signs of heat stroke and require emergency care.
Severe fluid or electrolyte loss can also cause fainting and injuries from a fall or collapse. Dehydration may worsen kidney problems or other underlying medical conditions, particularly when treatment is delayed.
Diagnosis
How Heat Exhaustion Is Diagnosed
Clinicians usually ask about recent heat exposure, physical activity, fluid intake, and the timing of symptoms. They check temperature, heart rate, blood pressure, hydration status, mental status, and skin findings. This assessment helps identify heat exhaustion and look for signs of a more serious heat-related illness.
Distinguishing heat exhaustion from other conditions
In heat exhaustion, a person may be weak, dizzy, sweaty, or nauseated but remains alert. Confusion, loss of consciousness, seizures, or other neurological changes raise concern for heat stroke, while dizziness, weakness, nausea, or fainting may also have causes unrelated to heat. Blood or urine tests may be used when symptoms are severe, prolonged, atypical, or concerning for electrolyte abnormalities or kidney problems.
Treatment & Management
Heat Exhaustion Treatment
Emergency action
Do not wait for symptoms to worsen
Get emergency medical help for confusion, unconsciousness, a seizure, inability to drink, repeated vomiting, or symptoms that do not improve with cooling. Never give fluids to a person who cannot swallow safely because they could choke.
Clinicians may monitor vital signs and hydration, order laboratory tests, or provide intravenous fluids when symptoms are severe or oral fluids are not enough. Avoid strenuous activity and further heat exposure until recovery, and seek advice before returning to work, exercise, or sports. How long heat exhaustion lasts varies with the severity of fluid loss, cooling, and the person’s overall health.
Prevention
How to Prevent Heat Exhaustion
- Drink fluids regularly instead of waiting until you feel very thirsty.
- Schedule outdoor work and exercise during cooler hours when possible.
- Take regular breaks in shade, air conditioning, or another cool place.
- Wear lightweight, loose-fitting, breathable clothing.
- Use shade, fans, or air conditioning to reduce exposure to excessive heat.
- Increase activity gradually over several days to help your body acclimatize.
- Never leave a person or child in a parked vehicle, even for a short time.
Outlook and Prognosis
Heat Exhaustion Recovery and Outlook
The outlook is generally favorable when heat exhaustion is recognized and treated promptly with cooling and safe fluid replacement. Symptoms should be taken seriously because untreated illness can worsen, and recovery is not guaranteed to follow the same pattern for everyone.
Recovery check
Know when to seek an evaluation
Ongoing heat exposure, dehydration, severe symptoms, older age, chronic disease, and delayed treatment can make recovery take longer. Arrange medical evaluation if symptoms persist, recur, or worsen, or if they include confusion, fainting, seizures, or an inability to keep fluids down.
When Should You See a Doctor
When Should You See a Doctor for Heat Exhaustion?
- Symptoms do not improve after moving to a cool place and cooling the body.
- Vomiting happens repeatedly.
- Severe weakness makes it difficult to stand or move safely.
- Fainting occurs.
- There are concerns about significant dehydration.
- The person has a high-risk medical condition or takes medication that may affect heat tolerance.
Call emergency services
Possible heat stroke
Call emergency services for confusion, altered behavior, loss of consciousness, seizures, a very high body temperature, inability to drink, or suspected heat stroke. Heat stroke is not the same as a brain stroke, but it is still life-threatening and requires immediate treatment. Begin cooling while waiting for help, but do not give fluids to someone who cannot swallow safely.
Symptoms
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