Heat Stroke (Sunstroke)

Reviewed on 7/29/2022

Heat Stroke Facts

Image of a woman suffering heat stroke
Image of a woman suffering heat stroke (sunstroke).
  • Heat stroke is a condition where the body's cooling mechanisms are overcome by heat resulting in a high core heat usually above 104 F or 40 C in adults, and 105 F or 40.5 C in children; and accompanied by mental status changes; heat stroke is a medical emergency.
  • Heat stroke is caused by a failure of the body's cooling mechanisms (sweating and/or evaporative cooling, for example) when exposed to heat.
  • Heat stroke symptoms are mainly increased body core temperature (see above) and mental status changes.
  • Heat stroke is diagnosed by the history, physical exam, and measurement of body core temperature.
  • Treatment of heat stroke is immediate cooling of the body by
    • placing the person in shade or an air-conditioned room, and by covering the person with cool evaporative mists or wet sheets with fans next to the person to increase evaporative cooling;
    • placing ice packs to the groin, armpits, neck, and head have also been recommended.
  • Recovery time for heat stroke is variable; initial recovery may be done with 1-2 days in the hospital; complete recovery may take about 2 months to a year.
  • Complications of heat stroke increase the longer it takes to begin treatment; complications can include
  • Heat stroke can be prevented by
    • drinking fluids,
    • limiting exposure to heat,
    • wearing clothing that allows evaporative cooling, and
    • recognizing the early warning signs of heat cramps and heat exhaustion and responding to those symptoms with treatment (cooling).
  • Do not leave infants, children, or pets in vehicles, and do not leave vehicles unlocked so children can get in them unattended to prevent deaths from heat stroke.

What Is the Definition of Heat Stroke?

Heat stroke is an emergency condition where the body's core temperature is markedly elevated (depending on who provides the definition, about 104 F [40 C] or above in adults and 105 F or 40.5 C in children) after being exposed to high environmental temperatures combined with neurologic symptoms and loss of body thermal autoregulation (ability of the brain to control the body temperature).

  • The elderly, pregnant females, and young children are at higher risk for heat stroke; their bodies do not cool as well as adults with no health problems). Some health-care professionals further subdivide heat strokes into exertional and non-exertional, but both have similar symptoms and treatments. Heat stroke has also been termed sunstroke and hyperthermia; heat stroke is a medical emergency.
  • Animals (dogs and cats, for example) can suffer heat stroke; symptoms of excessive panting and lethargy or unresponsiveness are usually diagnostic. The animal's Vet should be notified immediately; the treatments and outcomes are similar to those described below for humans.

What Are the Symptoms and Signs of Heat Stroke?

Heat Stroke Symptoms
The body can lose significant amounts of water when it tries to cool itself by sweating.
  • Heat stroke usually follows two other heat-related problems; heat cramps and heat exhaustion. These two conditions are marked by
  • As these conditions progress of heat cramps and heat exhaustion progress, these symptoms may occur
  • These symptoms may linger and progress to heat stroke when the body temperature reaches 104 F or 40 C or 105 F and 40.5 C in children, and the body stops sweating.
  • In addition to stopping sweating, the skin of a person suffering from a heat stroke is hot and dry, and sometimes becomes a reddish color.
  • Stroke-like symptoms occur in heat stroke.
    • Confusion,
    • hallucinations,
    • seizures,
    • loss of consciousness,
    • organ damage,
    • coma, and
    • death can occur if not treated quickly and effectively. 

The mental status changes help differentiate heat exhaustion from heat stroke.

What Causes Heat Stroke?

The major cause of heat stroke is prolonged exposure to high temperatures and/or doing strenuous activity in hot weather. The body's ability to control the core temperature (sweating, evaporative cooling, for example) is overwhelmed by heat.

Infants, children, pregnant females and the elderly are at higher risk for heat stroke because they are less able to control their core temperature.

Other causes that can contribute to the condition of heat stroke are:

  • Dehydration
  • Drinking alcohol
  • Dide effects of certain medications (for example, dehydration, increased urination, sweating)
  • Wearing excess and/or tight clothing can contribute to causing heat stroke by inhibiting cooling by evaporation.
  • Sunburn

Another cause of heat stroke that often results in death is leaving a child or pet in a vehicle that is not well ventilated or cooled. The average number of child fatalities due to heatstroke from being left in a car has averaged 37 deaths per year since 1998.

  • About 53% of the children were "forgotten" and left in a vehicle by an adult,
  • about 17% were intentionally left inside by an adult, and
  • the remainder were mainly children that shut themselves in an unattended vehicle.

When Should I Call the Doctor for Heat Stroke?

Heat stroke is a medical emergency; any signs or symptoms of this condition should prompt a call to emergency services (911).

  • Meanwhile, immediately begin first aid by cooling the person – move them to shade or an air-conditioned building,
  • remove constricting or clothing layers, and
  • cool the person with evaporative cooling (mist or spray water on the patient while fans are running).
  • Some experts recommend placing ice packs or wet towels to the head, neck, armpits, and groin.

How Is Heat Stroke Diagnosed?

The diagnosis of heat stroke is almost always made by the patient's symptoms, exposure to hot surroundings, and taking the core body temperature (rectal temperature).

  • Other tests are usually done to check electrolyte levels, urine studies for renal damage, liver damage, and rhabdomyolysis (muscle breakdown).
  • Tests such as chest X-ray, CT, or MRI may be ordered to search for additional organ damage.

What Is the Treatment for Heat Stroke?

Immediate treatment of heat stroke is body cooling;

  • currently the preferred method of cooling is evaporation cooling by spraying the patient with cold water or covering them with cold water soaked sheets, and
  • using fans to augment evaporative cooling.
  • Others recommend additional cooling by placing ice packs on the head, neck, armpits, and groin.
  • In addition, benzodiazepines can be administered to prevent shivering.
  • Often the patient is dehydrated so IV fluids are given.

The goal is to reach a core temperature (rectal probe reading with a constant readout) of below 102.2 F or 39 C. The ideal time frame for reaching this temperature is controversial but this should in general be achieved in the fastest possible time frame, ideally over the first 60 minutes. In addition, other supportive measures for breathing, hypotension, and seizures may be required.

How Can I Prevent Heat Stroke?

Heat strokes can be prevented; simple precautions can be very effective. Such precautions include:

  • Wear loose-fitting, light-colored clothing
  • Stay well hydrated; drink Gatorade or similar sports drinks - if you have infrequent urination or the urine is concentrated, you need more fluid intake (avoid alcohol)
  • Avoid hot sunlit areas and do not sit in a parked car (a common cause of heat stroke in children)
  • Avoid strenuous activity in the warmest part of the day
  • Some medications (diuretics, stimulants, sedatives, for example) can increase the risk of heat stroke; check with your pharmacist or doctor to see if you have increased risk because of your medications.
  • If you feel muscle cramps or feel weak, immediately stop the activity and cool down.
  • Acclimatize if you are traveling or moving to a hot climate by limiting outdoor activities for a few days or more if you have increased risk factors for heat-related illness.

What Is the Prognosis for Heat Stroke?

With quick and effective treatment, many people will recover with little or no problems, although some may become more sensitive to hot weather. Initial recovery takes about 1-2 days in the hospital; longer if organ damage is detected.

  • Experts suggest that complete recovery from heat stroke and its effects on the internal organs may take 2 months to a year. However, the prognosis rapidly declines as complications increase. The brain and other organs (lungs, liver, kidneys) can be permanently damaged, thus causing long-term effects on the person's health. Damage is caused by swelling due to heating and other mechanisms, so the prognosis in these patients may range from fair to poor.
  • Heat stroke outcomes in animals (for example, dogs and cats) are similar to that in humans; contact your animal's Vet for emergency medical care and for other details specific for your pet.

Dehydration Pictures: Prevention Tips!

Dehydration Prevention Tip #1

Plan ahead and take extra water to all outdoor events where increased sweating, activity, and heat stress will increase fluid loss. Encourage athletes and people who work outside to replace fluids at a rate that equals the loss.

Reviewed on 7/29/2022

American Family Physician. Evaluation and Treatment of Heat-Related Illnesses.

Humane Society. Keep Pets Safe in the Heat.

noheatstroke.org. Heatstroke Deaths of Children in Vehicles.

UpToDate. Heatstroke.