Heatstroke and heat exhaustion are illnesses caused by exposure to extreme heat. If left untreated, heat exhaustion can progress into heatstroke, which may be life-threatening.
According to the Centers for Disease Control and Prevention (CDC), above-average temperatures or unusually humid weather kills more than 600 people in the United States each year.
As temperatures rise, it is important to know how to avoid heat-related illnesses. Learn about the symptoms and treatments of heatstroke and heat exhaustion below.
These conditions both result from overexposure to extremely hot weather. However, only heatstroke can cause damage to the body’s systems.
Heatstroke, also called sunstroke, is the most serious heat-related illness. It occurs when the body’s temperature is 104ºF or higher, and it is a life-threatening medical emergency.
If not treated immediately, heatstroke can damage multiple organs and systems, including the:
- brain and nervous system
- circulatory system
- digestive tract
Heat exhaustion is less serious than heatstroke. Anyone who suspects that they have heat exhaustion should immediately rest and rehydrate. If symptoms do not improve, seek medical attention to prevent heatstroke.
Symptoms of heat exhaustion and heatstroke may develop quickly or over several days. They can cause significant distress, and muscle cramping often occurs first.
Heat exhaustion can lead to:
- muscle cramping
- a rapid, weak pulse
- a general sense of weakness
- nausea or vomiting
- excessive sweating
- cold, clammy skin
- dizziness and sometimes fainting
- dark-colored urine
Heatstroke may begin with symptoms of heat exhaustion. It can be life-threatening, and symptoms may rapidly worsen, to include:
- a temperature of 104ºF or higher
- hot, dry skin
- a racing heartbeat
- slurred speech
- loss of consciousness
There are two types of heatstroke: exertional and non-exertional.
Non-exertional heatstroke occurs in those who cannot adapt well to increasingly hot temperatures. Older adults, people with chronic illnesses, and infants are often affected.
A person typically experiences this type of heatstroke when they are indoors without air conditioning, and they may not be engaging in any physical activity. It can take several days of high temperatures for non-exertional heatstroke to occur, and it is common during extreme heat waves.
Exertional heatstroke occurs in people whose bodies can no longer adapt to rising temperatures while exercising or working. This condition can develop within a few hours, and it usually affects people who are spending time outdoors.
Spending time in closed cars puts small children and pets at high risk of heatstroke. The CDC estimate that when the temperature outdoors is 80ºF, the temperature inside a closed car rises to 109ºF within 20 minutes. The hotter it is outside, the faster the temperature rises inside a vehicle.
Anyone experiencing any symptoms of heatstroke should seek emergency medical attention.
If a person suspects that they have heat exhaustion, they should try to reverse the condition by moving into a cooler environment, resting, staying hydrated, and changing into cooler clothes.
If symptoms get worse or do not improve within 1 hour, seek immediate medical care.
A doctor will likely be able to diagnose a heat-related illness based on symptoms. They may also perform tests to check for potential complications.
For example, a doctor may test for:
- muscle damage
- dehydration, often with a urine sample or blood test
- heart and lung damage, possibly using imaging
- circulatory system problems
- a lack of kidney or liver function
Anyone who suspects that they have heat exhaustion should immediately take steps to cool down. These can include:
- moving to a shady location
- removing one or more articles of clothing
- resting out of the sun
- turning on a fan or the air conditioning
- running cool water over the skin or applying cool, wet towels to the body
- drinking fluids such as water and sports drinks
If a person vomits or feels nauseous, seek medical attention.
If a person exhibits any symptom of heatstroke, contact emergency services immediately. To treat it, a doctor may:
- apply ice packs to the neck, armpits, and groin
- spray cool mists
- support any injured organ systems
- use a specialized cooling blanket
- administer intravenous fluids that promote cooling and hydration
Certain factors can make a person more likely to experience heat exhaustion or heatstroke. These include:
- being overweight or obese
- having a significant disability
- having a sunburn
- being younger than 13 or older than 65
- using some prescription medications for heart conditions or high blood pressure, particularly diuretics
- experiencing sudden changes in temperature, such as by traveling from a cold to a hot climate
- spending time outdoors in extreme heat, or indoors without a way to cool down
When temperatures rise, it is important to know how to prevent heat-related illnesses. The goal is to keep the body cool.
The following strategies can help:
- staying indoors during the hottest part of the day
- trying to stay in the shade when outdoors
- drinking an extra 2–4 cups of water every hour while exposed to high temperatures
- taking frequent breaks when working or exercising outdoors on hot days
- wearing loose, light-colored clothing
- using cooler water for showers and baths
- wearing a wide-brimmed hat to shield the face from the sun
- avoiding drinks that dehydrate, including those with caffeine or alcohol
- wearing breathable fabrics like cotton, rather than synthetic blends
- spending part of the day in an air-conditioned place, such as a mall, library, or movie theater
No one should remain alone in a parked car in extremely hot weather. Doing so could be especially dangerous for children and people aged 65 and older.
With appropriate, timely treatment, a person can fully recover from heat-related illnesses.
Recognizing symptoms of heat exhaustion and taking steps to cool down can prevent the condition from developing into heatstroke.
If left untreated, heatstroke can result in serious complications or death. When a person receives the right treatment early enough, they can fully recover from heatstroke.
Even on the hottest days, these illnesses can usually be prevented by planning and taking precautions.