Exertional Heat Stroke 101: What You Should Know

Heat stroke.

You’ve heard of it, you may have witnessed it, and maybe you’ve even experienced it. It’s a condition that tends to occur more often when the weather heats up and people are spending more time outside.1 Sometimes heat-related illness is met with a dangerously nonchalant attitude, but exertional heat stroke (EHS) is different. Exertional heat stroke is unknown to many, very dangerous, and could be life-threatening.2 On top of its serious health impact, the broad spectrum of those who may be affected might surprise you. But don’t panic, we’re here to help shed some light on this lesser known heat-related illness, so you can recognize the signs and symptoms before it’s too late. We’ll provide you with information on EHS to make you feel more confident and informed about this condition, and what to do if you encounter it.

But first, what is it, and why is it important?

Exertional heat stroke, or EHS, is a severe form of heat-related illness that can result in organ damage, or even death in some cases.2 While classic heat stroke tends to be brought on by environmental heat, EHS occurs when you add physical exertion to particularly hot and humid conditions.* So, when it’s hot and humid and physical activity is involved – say playing sports, for example – that’s when EHS is more likely to rear its ugly head.

(*EHS is more likely to occur particularly in hot and humid environments, but people can be at risk in other environmental conditions, too.3,4,5)

EHS 101 image

How does it happen?

EHS happens when someone exerts energy during physical activity and causes his or her body temperature to rise to a dangerous level (104°F or greater),†6 putting vital organs at risk for permanent damage.2 If the body’s core temperature stays at these dangerous levels for too long and is not cooled quickly, EHS could become deadly in some cases.7

The effects of EHS can occur rapidly,8 so it’s important to keep an eye out for some of the signs and symptoms:6

    • Fainting/dizziness
    • Vomiting
    • Confusion or disorientation
    • Unusual behavior (e.g., aggression)

Who is at risk?

EHS can happen to any active person pushed to his or her limits, regardless of age or physical ability.3,4,5 Any strenuous activity, such as mowing the lawn or dancing at a concert, can lead to EHS when in particularly hot temperature conditions.1

Firefighters, outdoor workers and military personnel operating in high-temperature conditions are among those at risk.1 Athletes especially are at risk: EHS is considered the third leading cause of sudden death in high school athletes.5,8 But it doesn’t have to be.

How can we protect ourselves?

Protection and quick action are key when it comes to EHS, but it takes awareness and some essential knowledge to understand what is happening and how to address it. This easy-to-memorize acronym will help in identifying EHS:

H – High temperature
E – Exercise or activity
A – Acting confused
T – Time to call 911

H.E.A.T. – get it?

In order to help protect yourself and those you care about from EHS, the best thing you can do is spread the word. It could save a life.


Measured rectally


1. Leon LR, Helwig BG. Heat stroke: role of the systemic inflammatory response. J Appl Physiol. 2010;109:1980-1988. doi:10.1152/japplphysiol.00301.2010.

2. Walter EJ, Carraretto M. The neurological and cognitive consequences of hyperthermia. Critical Care. 2016;20(199). doi:10.1186/s13054-016-1376-4.

3. Becker JA, Stewart LK. Heat-related illness. Am Fam Physician. 2011;83(11):1325-1330.

4. Epstein Y, Moran DS, Shapiro Y. Exertional heatstroke in the Israeli defence forces. In: Pandoff KB, Burr RE, eds. Medical Aspects of Harsh Environments. Volume 1. Office of the Surgeon General, United States Army. 2002;281-292.

5. King MA, Leon LR, Mustico DL, Haines JM, Clanton TL. Biomarkers of multiorgan injury in a preclinical model of exertional heat stroke. J Appl Physiol. 2015;118:1207-1220. doi:10.1152/japplphysiol.01051.2014.

6. Casa DJ, DeMartini JK, Bergeron MF, Csillan D, Eichner R, Lopez RM, Ferrara MS, Miller KC, O’Connor F, Sawka M, Yeargin SW. National athletic trainers’ association position statement: exertional heat illness. J Athl Train. 2015;50(9):986-1000.doi10.4085/1062-6050-50.9.07

7. Bouchama A, Roberts G, Al Mohanna F, et al. Inflammatory, hemostatic, and clinical changes in a baboon experimental model for heatstroke. J Appl Physiol. 2005;98(697–705). doi:10.1152/japplphysiol.00461.2004.

8. Jardine DS. Heat illness and heat stroke. Pediatr Rev Am Acad Pediatric. 2007;28(7). doi:10.1542/pir.28-7-249