When Heat Exhaustion Becomes Heat Stroke
Most people associate heat illness with deserts, tropical climates, or overseas holidays.
Not the UK.
Yet every year, people become seriously unwell during periods of hot weather. Walkers, runners, horse riders, outdoor workers, instructors, festival-goers, and even spectators can all be affected.
The problem is that heat illness rarely starts as an emergency.
It starts with feeling a bit tired.
A little dizzy.
A headache.
Something that is easy to ignore.
Until it isn't.
Your Body's Cooling System
Your body works hard to maintain a core temperature of around 37°C.
When you get hot, blood vessels near the skin widen and sweating increases. As sweat evaporates, heat is removed from the body.
Simple.
But this system has limits.
High temperatures, humidity, dehydration, strenuous exercise, heavy clothing, protective equipment, or simply prolonged exposure to the sun can overwhelm your body's ability to cool itself. When that happens, heat illness begins.
Recognising Heat Exhaustion
Heat exhaustion is the body's warning sign.
It means the cooling system is struggling but still working.
Common symptoms include:
Headache
Dizziness or light-headedness
Feeling weak or tired
Nausea or vomiting
Muscle cramps
Heavy sweating
Pale, cool or clammy skin
Fast breathing or increased heart rate
Excessive thirst
A temperature usually above 38°C
Heat exhaustion is unpleasant, but it is usually reversible if recognised early and managed appropriately.
When Things Become Dangerous
This is where many people get caught out.
Heat stroke is not simply "bad heat exhaustion."
Heat stroke occurs when the body's temperature regulation system starts to fail.
The casualty is no longer effectively cooling themselves.
Core temperature continues to rise.
Organs begin to suffer.
Without rapid treatment, heat stroke can cause brain injury, organ failure, and death.
The Red Flags of Heat Stroke
If someone develops any of the following, treat it as a medical emergency:
Confusion
Altered behaviour
Agitation or unusual irritability
Collapse
Seizures
Reduced level of consciousness
Unresponsiveness
Very hot skin
A temperature approaching or exceeding 40°C
One important point.
Many people are taught that heat stroke means "hot and dry skin."
While that can occur, particularly in classic heat stroke, people can still be sweating when heat stroke develops, especially after physical activity.
Do not wait for sweating to stop before acting. Changes in mental state are often the most important warning sign.
First Aid for Heat Exhaustion
The aim is simple.
Cool them down.
Move them into shade or a cool environment.
Remove unnecessary clothing.
Encourage rest.
Offer cool water or an oral rehydration drink if they are able to drink safely.
Cool the skin using water, damp clothing, fanning, or cool packs wrapped in cloth placed around the neck, armpits, or groin.
Most people should improve within 30 minutes.
If they do not improve, seek medical advice as heat stroke may be developing.
First Aid for Heat Stroke
Heat stroke is a 999 emergency.
Call for help immediately.
While waiting:
Move the casualty to a cool environment.
Remove excess clothing.
Actively cool them with water, wet towels, or damp sheets.
Fan continuously if possible.
Monitor their airway and breathing.
Place an unconscious casualty in the recovery position if breathing normally.
Do not delay calling for help while trying to cool them. Both need to happen.
Why This Matters for Outdoor Activities
In the UK, we often underestimate heat.
Many outdoor incidents happen because people prepare for rain, wind, and cold but fail to prepare for hot conditions.
I've seen people prepped for adventure, carrying waterproofs, spare layers, and emergency shelters, yet not enough water.
The reality is that heat can be every bit as dangerous as cold.
Whether you're walking in the Chilterns, climbing in Snowdonia, riding at an event, or leading a Duke of Edinburgh expedition, recognising the early signs of heat illness can prevent a minor problem becoming a life-threatening emergency.
Final Thoughts
Heat exhaustion is a warning.
Heat stroke is an emergency.
The challenge is recognising the point where one becomes the other.
If someone is becoming confused, behaving unusually, collapsing, or failing to improve despite cooling measures, stop thinking about heat exhaustion and start treating for heat stroke.
Because by that stage, time matters.
Be Adventure Ready.
References
NHS. Heat Exhaustion and Heatstroke. Available at: https://www.nhs.uk/conditions/heat-exhaustion-heatstroke/
UK Health Security Agency. Beat the Heat: Staying Safe in Hot Weather. Available at: https://www.gov.uk/government/publications/beat-the-heat-hot-weather-advice
British Red Cross. Heatstroke First Aid. Available at: https://www.redcross.org.uk/first-aid/learn-first-aid/heatstroke
Health and Safety Executive. Heat Stress in the Workplace. Available at: https://www.hse.gov.uk/temperature/employer/heat-stress.htm
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