What’s the difference between heat exhaustion and heat stroke? One’s a medical emergency
- Written by: Matthew Barton, Senior lecturer, School of Nursing and Midwifery, Griffith University
When British TV doctor Michael Mosley died last year in Greece after walking in extreme heat, local police said “heat exhaustion” was a contributing factor.
Since than a coroner could not find a definitive cause of death but said this was most likely due to an un-identified medical reason or heat stroke.
Heat exhaustion and heat stroke are two illnesses that relate to heat.
So what’s the difference?
A spectrum of conditions
Heat-related illnesses range from mild to severe. They’re caused by exposure to excessive heat, whether from hot conditions, physical exertion, or both. The most common ones include:
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heat oedema: swelling of the hands, feet and ankles
heat cramps: painful, involuntary muscle spasms usually after exercise
heat syncope: fainting due to overheating
heat exhaustion: when the body loses water due to excessive sweating, leading to a rise in core body temperature (but still under 40°C). Symptoms include lethargy, weakness and dizziness, but there’s no change to consciousness or mental clarity
heat stroke: a medical emergency when the core body temperature is over 40°C. This can lead to serious problems related to the nervous system, such as confusion, seizures and unconsciousness including coma, leading to death.
As you can see from the diagram below, some symptoms of heat stroke and heat exhaustion overlap. This makes it hard to recognise the difference, even for medical professionals.
Firefighters are among those at risk of heat-related illness.
structuresxx/Shutterstock
How are these conditions managed?
The risk of serious illness or death from heat-related conditions is very low if treatment starts early.
For heat exhaustion, have the individual lie down in a cool, shady area, loosen or remove excess clothing, and cool them by fanning, moistening their skin, or immersing their hands and feet in cold water.
As people with heat exhaustion almost always are dehydrated and have low electrolytes (certain minerals in the blood), they will usually need to drink fluids.
However, emergency hospital care is essential for heat stroke. In hospital, health professionals will focus on stabilising the patient’s:
airway (ensure no obstructions, for instance, vomit)
breathing (look for signs of respiratory distress or oxygen deprivation)
circulation (check pulse, blood pressure and signs of shock).
Meanwhile, they will use rapid-cooling techniques including immersing the whole body in cold water, or applying wet ice packs covering the whole body.
Take home points
Heat-related illnesses, such as heat stroke and heat exhaustion, are serious health conditions that can lead to severe illness, or even death.
With climate change, heat-related illness will become more common and more severe. So recognising the early signs and responding promptly are crucial to prevent serious complications.
Authors: Matthew Barton, Senior lecturer, School of Nursing and Midwifery, Griffith University 
