What's the difference between heat exhaustion and heatstroke?

As global temperatures rise, it's important to understand the risks associated with extreme heat. While most people have heard of heat exhaustion and heatstroke, knowing the differences between the two could save a life.

During a heatwave in September 2023, there were 934 heat-associated deaths in England alone in just an 11-day period. Two of the most common conditions caused by the heat are heat exhaustion and heatstroke.

These illnesses can affect anyone, at any time, but are widely misunderstood. If not treated early and quickly, can develop into something serious and potentially life-threatening.

We'll look at some common misconceptions about heat exhaustion and heatstroke. Understanding the difference between the two could help save a life.

 

Heat exhaustion vs. heatstroke: what’s the difference?

When someone’s feeling drained after a hot day in the sun, it’s not unusual to hear them say, “I think I have heatstroke,” or “I’ve had too much sun.” But often, what they’re experiencing is heat exhaustion, not heatstroke. 

Heat exhaustion is the body’s warning system. It is caused by a loss of salt and water from the body. If heat exhaustion isn’t spotted and managed quickly, it can progress to heatstroke, which is far more serious. 

Heatstroke is a failure of the body’s ‘thermostat’. It occurs when the body is no longer able to control its temperature. It’s a medical emergency that can lead to permanent organ damage or death if not treated rapidly. 

Understanding this difference is important as more frequent and intense heatwaves hit the UK each year.

Most of us have felt uncomfortable in hot weather at some point. Thankfully, our bodies do a good job of managing temperature, but when things start to go wrong, it’s not always easy to spot the warning signs. Someone might not realise they're in trouble until it becomes serious, which is where a first aider can step in and make a difference.

- Alice Squires, Red Cross First Aid Training team.

What it feels like to have heat exhaustion

Heat exhaustion can come on gradually or suddenly. You may feel: 

• headache
• dizziness and confusion
• loss of appetite
• nausea
• sweating
• cramps in the arms , legs, or stomach
• a fast but weak pulse
• pale or clammy skin

 

First aid action for heat exhaustion

These signs and symptoms are the body’s way of saying it needs to cool down quickly. If someone is showing these signs, you should:

• move them to a cool place
• rehydrate them
• make them rest

For more information see our page on first aid for heat exhaustion.

What it feels like to have heatstroke

Heatstroke is a medical emergency and feels very different from heat exhaustion. It can come on quickly, especially if heat exhaustion goes unnoticed or untreated. You may experience: 

• a dangerously high body temperature, often above 40°C 
• hot, flushed and dry skin
• headache, dizziness and discomfort
• restlessness and confusion
• rapid deterioration in the level of response
• full, bounding pulse
• seizures, or in severe cases, loss of consciousness

 

First aid action for heatstroke

Without urgent medical attention, heatstroke can cause lasting damage to the brain, heart, kidneys, and muscles. Acting quickly is crucial. If someone is showing signs of heatstroke, you should:

• call 999 immediately
• begin to cool them down while waiting for emergency services
• move them to a cooler area
• wrap them in a cool, wet sheet, keeping the sheet damp by continuously pouring cold water over it

For more information, see our page on first aid for heatstroke.

How to tell if it’s heat exhaustion or heatstroke?

It’s important to know the difference between signs and symptoms. Signs can be seen by someone else for example, a doctor or bystander. These include things like pale skin, sweating, or fast breathing. 

Symptoms are what the person experiences and says they have, for example, pain, dizziness, or nausea.

Here are the key differences in signs and symptoms: 

Body temperature

• heat exhaustion: normal or slightly high
• heatstroke: above 40°C (104°F)

Responsiveness

• heat exhaustion: tired, dizzy, but alert
• heatstroke: confused, unconscious, or seizures

Skin

• heat exhaustion: pale and clammy
• heatstroke: hot and dry

Sweating

• heat exhaustion: heavy
• heatstroke: little or none

Pulse

• heat exhaustion: fast but weak
• heatstroke: rapid and strong

 

 

Prepare for hot weather

Prevent heat exhaustion and heatstroke occurring

During hot weather, you should:

• make sure you have a bottled water for drinking
• take a handheld electric fan, cooling wipes, and a thermometer with you
• check on neighbours, friends, or relatives who might be more vulnerable

Learn how to help others who are unwell

• learn first aid skills for heat exhaustion and heatstroke
• be alert how people around you are feeling, especially young children, older adults, people with long-term health conditions, or those working outside or in hot indoor environments.

Learn how to help yourself if you are unwell

• pay attention to how you're feeling, particularly to any changes in how you're feeling
• do not do things in hot weather alone, as someone else may spot signs that you have not noticed yourself
• do not hesitate to ask for help if you feel any symptoms

More resources on staying safe in the heat

• Read our tips on how to keep cool at night
• Here's how to cool down during hot weather
• Learn how to keep your home cool