Heat stroke or heatstroke, also known as sun stroke, is a severe heat illness that results in a body temperature greater than 40.0 °C (104.0 °F),[4] along with red skin, headache, dizziness, and confusion.[2] Sweating is generally present in exertional heatstroke, but not in classic heatstroke.[5] The start of heat stroke can be sudden or gradual.[3] Heatstroke is a life-threatening condition due to the potential for multi-organ dysfunction,[6] with typical complications including seizures, rhabdomyolysis, or kidney failure.[3]

Heat stroke
Other namesSun stroke, siriasis[1]
The British Army in the Middle East 1943 E26027.jpg
Person being cooled with water spray, one of the treatments of heat stroke, in Iraq in 1943
SpecialtyEmergency medicine
SymptomsHigh body temperature, red, dry or damp skin, headache, dizziness, confusion, nausea[2]
ComplicationsSeizures, rhabdomyolysis, kidney failure[3]
TypesClassic, exertional[3]
CausesHigh external temperatures, physical exertion[3][4]
Risk factorsExtremes of age, heat waves, high humidity, certain drugs, heart disease, skin disorders[3]
Diagnostic methodBased on symptoms[3]
Differential diagnosisNeuroleptic malignant syndrome, malaria, meningitis[3]
TreatmentRapid cooling, supportive care[4]
PrognosisRisk of death <5% (exercise induced), up to 65% (non exercise induced)[3]
Deaths> 600 per year (US)[4]

Heat stroke occurs because of high external temperatures and/or physical exertion.[3][4] It usually occurs under preventable prolonged exposure to extreme environmental or exertional heat.[6] However, certain health conditions can increase the risk of heat stroke, and patients, especially children, with certain genetic predispositions are vulnerable to heatstroke under relatively mild conditions.[7]

Preventive measures include drinking sufficient fluids and avoiding excessive heat.[8] Treatment is by rapid physical cooling of the body and supportive care.[4] Recommended methods include spraying the person with water and using a fan, putting the person in ice water, or giving cold intravenous fluids.[4] Adding ice packs around a person is reasonable but does not by itself achieve the fastest possible cooling.[4]

Heat stroke results in more than 600 deaths a year in the United States.[4] Rates have increased between 1995 and 2015.[3] Purely exercise-induced heat stroke, though a medical emergency, tends to be self-limiting (the patient stops exercising from cramp or exhaustion) and fewer than 5% of cases are fatal. Non-exertional heatstroke is a much greater danger: even the healthiest person, if left in a heatstroke-inducing environment without medical attention, will continue to deteriorate to the point of death, and 65% of the most severe cases are fatal even with treatment.[3]

Signs and symptomsEdit

Heat stroke generally presents with a hyperthermia of greater than 40.6 °C (105.1 °F) in combination with disorientation.[5][9] However, high body temperature does not necessarily indicate that heat stroke is present, such as with people in high-performance endurance sports or with people experiencing fevers.[10] Exertional heat stroke is more accurately diagnosed based on a constellation of symptoms rather than just a specific temperature threshold.[10] There is generally a lack of sweating in classic heatstroke, while sweating is generally present in exertional heatstroke.[5]

Early symptoms of heat stroke include behavioral changes, confusion, delirium, dizziness, weakness, agitation, combativeness, slurred speech, nausea, and vomiting.[5] In some individuals with exertional heatstroke, seizures and sphincter incontinence have also been reported.[5] Additionally, in exertional heat stroke, the affected person may sweat excessively.[11] If treatment is delayed, patients could develop vital organ damage, unconsciousness and even organ failure. In the absence of prompt and adequate treatment, heatstroke can be fatal.[12]


Heat stroke occurs when thermoregulation is overwhelmed by a combination of excessive metabolic production of heat (exertion), excessive heat in the physical environment, and insufficient or impaired heat loss, resulting in an abnormally high body temperature. Substances that inhibit cooling and cause dehydration such as alcohol, stimulants, medications, and age-related physiological changes predispose to so-called "classic" or non-exertional heat stroke (NEHS), most often in elderly and infirm individuals in summer situations with insufficient ventilation.[13]

Exertional heat strokeEdit

Exertional heat stroke (EHS) can happen in young people without health problems or medications – most often in athletes, outdoor laborers, or military personnel engaged in strenuous hot-weather activity or in first responders wearing heavy personal protective equipment. In environments that are not only hot but also humid, it is important to recognize that humidity reduces the degree to which the body can cool itself by perspiration and evaporation. For humans and other warm-blooded animals, excessive body temperature can disrupt enzymes regulating biochemical reactions that are essential for cellular respiration and the functioning of major organs.[12]


When the outside temperature is 21 °C (70 °F), the temperature inside a car parked in direct sunlight can quickly exceed 49 °C (120 °F). Young children or elderly adults left alone in a vehicle are at particular risk of succumbing to heat stroke. "Heat stroke in children and in the elderly can occur within minutes, even if a car window is opened slightly."[14] As these groups of individuals may not be able to open car doors or to express discomfort verbally (or audibly, inside a closed car), their plight may not be immediately noticed by others in the vicinity. In 2018, 51 children in the United States died in hot cars, more than the previous high of 49 in 2010.[15]

Dogs are even more susceptible than humans to heat stroke in cars, as they cannot produce whole-body sweat to cool themselves. Leaving the dog at home with plenty of water on hot days is recommended instead, or, if a dog must be brought along, it can be tied up in the shade outside the destination and provided with a full water bowl.[16]


The pathophysiology of heat stroke involves an intense heat overload followed by a failure of the body's thermoregulatory mechanisms. More specifically, heat stroke leads to inflammatory and coagulation responses that can damage the vascular endothelium and result in numerous platelet complications, including decreased platelet counts, platelet clumping, and suppressed platelet release from bone marrow.[17]

Growing evidence also suggests the existence of a second pathway underlying heat stroke that involves heat and exercise-driven endotoxemia.[18] Although its exact mechanism is not yet fully understood, this model theorizes that extreme exercise and heat disrupt the intestinal barrier by making it more permeable and allowing lipopolysaccharides (LPS) from gram-negative bacteria within the gut to move into the circulatory system.[18] High blood LPS levels can then trigger a systemic inflammatory response and eventually lead to sepsis and related consequences like blood coagulation, multi-organ failure, necrosis, and central nervous system dysfunction.[18]


In terms of the diagnosis for this condition one sees the following (though this is not a complete list):[19]


The risk of heat stroke can be reduced by observing precautions to avoid overheating and dehydration. Light, loose-fitting clothes will allow perspiration to evaporate and cool the body. Wide-brimmed hats in light colors help prevent the sun from warming the head and neck. Vents on a hat will help cool the head, as will sweatbands wetted with cool water. Strenuous exercise should be avoided during hot weather, especially in the sun peak hours as well as avoiding confined spaces (such as automobiles) without air-conditioning or adequate ventilation.[medical citation needed]

In hot weather, people need to drink plenty of cool liquids and mineral salts to replace fluids lost from sweating. Thirst is not a reliable sign that a person needs fluids. A better indicator is the color of urine. A dark yellow color may indicate dehydration.[11]

Example of a checklist designed to help protect workers from heat stress:[20]

  • Know signs/symptoms of heat-related illnesses.
  • Block out direct sun and other heat sources.
  • Drink fluids often, and before you are thirsty.
  • Wear lightweight, light-colored, loose-fitting clothes.
  • Avoid beverages containing alcohol or caffeine.


Treatment of heat stroke involves rapid mechanical cooling along with standard resuscitation measures.[21]

The body temperature must be lowered quickly via conduction, convection, or evaporation.[4] The person should be moved to a cool area, such as indoors or to a shaded area. Clothing should be removed to promote heat loss through passive cooling. Conductive cooling methods such as ice-water immersion should also be used, if possible. Evaporative and convective cooling by a combination of cool water spray or cold compresses with constant air flow over the body, such as with a fan or air-conditioning unit, is also an effective alternative.[4] The person should not be wrapped in wet towels or clothing as this can act as insulation and increase the body temperature.[medical citation needed]

Aggressive ice-water immersion remains the gold standard for life-threatening heat stroke.[22][23] This method may require the effort of several people and the person should be monitored carefully during the treatment process. Immersion should be avoided for an unconscious person, but if there is no alternative, the person's head must be held above water.

Immersion in very cold water was once thought to be counterproductive by reducing blood flow to the skin and thereby preventing heat from escaping the body core. However, research has shown that this mechanism does not play a dominant role in the decrease in core body temperature brought on by cold water. Dantrolene, a muscle relaxant used to treat other forms of hyperthermia, is not an effective treatment for heat stroke.[24]

Hydration is important in cooling the person. In mild cases of concomitant dehydration, this can be achieved by drinking water, or commercial isotonic sports drinks may be used as a substitute.[medical citation needed] In either exercise- or heat-induced dehydration, electrolyte imbalance can result, and can be worsened by excess consumption of water.[medical citation needed] Hyponatremia can be corrected by intake of hypertonic fluids. Absorption is rapid and complete in most people but if the person is confused, unconscious, or unable to tolerate oral fluid, then an intravenous drip may be necessary for rehydration and electrolyte replacement.[medical citation needed]

The person's condition should be reassessed and stabilized by trained medical personnel. The person's heart rate and breathing should be monitored, and cardiopulmonary resuscitation (CPR) may be necessary if the person goes into cardiac arrest.


It was long believed that heat strokes lead only rarely to permanent deficits and that convalescence is almost complete. However, following the 1995 Chicago heat wave, researchers from the University of Chicago Medical Center studied all 58 patients with heat stroke severe enough to require intensive care at 12 area hospitals between July 12 and 20, 1995, ranging in age from 25 to 95 years. Nearly half of these patients died within a year – 21 percent before and 28 percent after release from the hospital. Many of the survivors had permanent loss of independent function; one-third had severe functional impairment at discharge, and none of them had improved after one year. The study also recognized that because of overcrowded conditions in all the participating hospitals during the crisis, the immediate care – which is critical – was not as comprehensive as it should have been.[25]

In rare cases, brain damage has been reported as a permanent sequela of severe heat stroke, most commonly cerebellar atrophy.[26][27]


There are various aspects that can affect the incidence of heat stroke. Including sex, age, geographical location, and even occupation. The incidence of heat stroke is higher among men however, the incidence of other heat illnesses is higher among women.[28] The incidence of other heat illnesses in women compared with men ranged from 1.30 to 2.89 per 1000 person-years versus 0.98 to 1.98 per 1000 person-years.[28]

Different parts of the world also have different rates of heat stroke.[medical citation needed]

During the 2022 European heat wave, almost twelve thousand people died from heatstrokes.

Society and cultureEdit

In Slavic mythology, there is a personification of sunstroke, Poludnitsa (lady midday), a feminine demon clad in white that causes impairment or death to people working in the fields at midday. There was a traditional short break in harvest work at noon, to avoid attack by the demon. Antonín Dvořák's symphonic poem, The Noon Witch, was inspired by this tradition.

Other animalsEdit

Heatstroke can affect livestock, especially in hot, humid weather; or if the horse, cow, sheep or other is unfit, overweight, has a dense coat, is overworked, or is left in a horsebox in full sun. Symptoms include drooling, panting, high temperature, sweating, and rapid pulse.

The animal should be moved to shade, drenched in cold water and offered water or electrolyte to drink.[29]

See alsoEdit


  1. ^ Herrick RT (April 1986). "Heat illness in the athlete: siriasis is serious". Alabama Medicine. 55 (10): 28, 33–28, 37. PMID 3706086.
  2. ^ a b "Warning Signs and Symptoms of Heat-Related Illness". www.cdc.gov. Archived from the original on July 13, 2017. Retrieved July 17, 2017.
  3. ^ a b c d e f g h i j k l Leon LR, Bouchama A (April 2015). "Heat stroke". Comprehensive Physiology. 5 (2): 611–647. doi:10.1002/cphy.c140017. ISBN 9780470650714. PMID 25880507.
  4. ^ a b c d e f g h i j k Gaudio FG, Grissom CK (April 2016). "Cooling Methods in Heat Stroke". The Journal of Emergency Medicine. 50 (4): 607–616. doi:10.1016/j.jemermed.2015.09.014. PMID 26525947.
  5. ^ a b c d e Epstein Y, Yanovich R (June 2019). "Heatstroke". The New England Journal of Medicine. 380 (25): 2449–2459. doi:10.1056/NEJMra1810762. PMID 31216400.
  6. ^ a b Bouchama A, Knochel JP (June 2002). "Heat stroke". The New England Journal of Medicine. 346 (25): 1978–1988. doi:10.1056/nejmra011089. PMID 12075060.
  7. ^ Wang HJ, Lee CS, Yee RS, Groom L, Friedman I, Babcock L, et al. (October 2020). "Adaptive thermogenesis enhances the life-threatening response to heat in mice with an Ryr1 mutation". Nature Communications. 11 (1): 5099. doi:10.1038/s41467-020-18865-z. PMC 7547078. PMID 33037202.
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  9. ^ McGugan EA (March 2001). "Hyperpyrexia in the emergency department". Emergency Medicine. 13 (1): 116–120. doi:10.1046/j.1442-2026.2001.00189.x. PMID 11476402.
  10. ^ a b Laitano O, Leon LR, Roberts WO, Sawka MN (November 2019). "Controversies in exertional heat stroke diagnosis, prevention, and treatment". Journal of Applied Physiology. 127 (5): 1338–1348. doi:10.1152/japplphysiol.00452.2019. PMID 31545156.
  11. ^ a b "InfoSheet: Protecting Workers from Heat Illness" (PDF). OSHA–NIOSH. 2011. Archived (PDF) from the original on June 16, 2015. Retrieved February 10, 2015.
  12. ^ a b Fauci, Anthony; et al. (2008). Harrison's Principles of Internal Medicine (17th ed.). McGraw-Hill Professional. pp. 117–121. ISBN 978-0-07-146633-2.
  13. ^ "Heat emergencies: MedlinePlus Medical Encyclopedia". www.nlm.nih.gov. Archived from the original on January 5, 2016. Retrieved January 19, 2016.
  14. ^ Meadows M (2014). "A primer on summer safety". Academic OneFile. Archived from the original on October 5, 2016. Retrieved January 18, 2016.
  15. ^ "2018 was Deadliest Year on Record for Hot Car Deaths". National Safety Council. Retrieved July 8, 2019.
  16. ^ "Dogs in Hot Cars". Partnership for Animal Welfare. Archived from the original on February 10, 2015. Retrieved February 11, 2015.
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  18. ^ a b c Lim CL (October 2018). "Heat Sepsis Precedes Heat Toxicity in the Pathophysiology of Heat Stroke-A New Paradigm on an Ancient Disease". Antioxidants. 7 (11): 149. doi:10.3390/antiox7110149. PMC 6262330. PMID 30366410.
  19. ^ Morris, Andrew; Patel, Gaurav (2022). "Heat Stroke". StatPearls. StatPearls Publishing. PMID 30725820. Retrieved May 12, 2022.
  20. ^ "QuickCard: Protecting Workers from Heat Stress" (PDF). OSHA. 2014. Archived (PDF) from the original on January 17, 2015. Retrieved February 10, 2015.
  21. ^ Tintinalli, Judith (2004). Emergency Medicine: A Comprehensive Study Guide (6th ed.). McGraw-Hill Professional. p. 1188. ISBN 0-07-138875-3.
  22. ^ McDermott BP, Casa DJ, Ganio MS, Lopez RM, Yeargin SW, Armstrong LE, Maresh CM (January 1, 2009). "Acute whole-body cooling for exercise-induced hyperthermia: a systematic review". Journal of Athletic Training. 44 (1): 84–93. doi:10.4085/1062-6050-44.1.84. PMC 2629045. PMID 19180223.
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  24. ^ Laitano O, Murray KO, Leon LR (September 2020). "Overlapping Mechanisms of Exertional Heat Stroke and Malignant Hyperthermia: Evidence vs. Conjecture". Sports Medicine. 50 (9): 1581–1592. doi:10.1007/s40279-020-01318-4. PMID 32632746. S2CID 220351326.
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  26. ^ Bouchama A, Knochel JP (June 2002). "Heat stroke". The New England Journal of Medicine. 346 (25): 1978–1988. doi:10.1056/NEJMra011089. PMID 12075060.
  27. ^ Bazille C, Megarbane B, Bensimhon D, Lavergne-Slove A, Baglin AC, Loirat P, et al. (November 2005). "Brain damage after heat stroke". Journal of Neuropathology and Experimental Neurology. 64 (11): 970–975. doi:10.1097/01.jnen.0000186924.88333.0d. PMID 16254491.
  28. ^ a b Alele F, Malau-Aduli B, Malau-Aduli A, Crowe M (April 2020). "Systematic review of gender differences in the epidemiology and risk factors of exertional heat illness and heat tolerance in the armed forces". BMJ Open. 10 (4): e031825. doi:10.1136/bmjopen-2019-031825. PMC 7245403. PMID 32265238.
  29. ^ Horse and Hound, 'First Aid: Handling Heatstroke', 2/8/2004

External linksEdit