Heat stroke is one of the most serious forms of heat-related illness. It occurs when the body’s temperature regulation system fails and core body temperature rises to dangerous levels. This can happen during hot weather, prolonged sun exposure, or vigorous physical activity in very warm conditions. Heat stroke is a medical emergency. Recognising the signs early and responding quickly can save lives.
What exactly is heat stroke?
Heat stroke happens when your body can no longer cool itself effectively. Normally, the body cools down by sweating and releasing heat through the skin. But in certain conditions — especially high environmental temperatures and humidity — this system becomes overwhelmed. If cooling mechanisms fail, a casualty’s internal temperature can rise rapidly, sometimes exceeding 40°C.
There are two main types of heat stroke:
Classic heat stroke: Develops over time in hot conditions, often affecting older adults and people with health issues.
Exertional heat stroke: Happens during strenuous physical activity, even in healthy individuals, particularly when it’s very hot and humid.
What are the early symptoms of heat stroke?
Recognising warning signs early can prevent heat stroke from becoming life-threatening. Key symptoms include:
Extreme body temperature: A core body temperature above 40°C is a hallmark of heat stroke.
Mental changes: Confusion, agitation, slurred speech, irrational behaviour or loss of awareness are serious signs that the brain is affected by overheating.
Changes in skin and sweating: In some cases, skin becomes hot and dry because the body stops sweating. In other cases, especially exertional heat stroke, the skin may still be damp or sweaty.
Rapid heartbeat and breathing: The cardiovascular system works harder to try and cool the body, leading to a fast pulse and fast breathing.
Other warning signs: Dizziness, headache, nausea, fainting, seizures, or muscle cramps may also occur.
These symptoms often develop quickly and require immediate attention. Heat stroke is a medical emergency and should never be treated lightly.
How can you tell heat stroke apart from heat exhaustion?
Heat exhaustion is a milder form of heat illness that can precede heat stroke. It usually involves heavy sweating, weakness, nausea, and a rapid pulse, but the casualty’s temperature is lower than with heat stroke and their level of consciousness is generally normal. It’s still important to take heat exhaustion seriously, however, as heat exhaustion can progress into heat stroke if left untreated or unaddressed.
Who is most at risk of heat stroke?
Heat stroke can affect anyone exposed to excessive heat, but certain groups are particularly vulnerable:
- Older adults and young children whose bodies are less efficient at temperature regulation
- People with chronic illnesses such as heart disease or diabetes
- Outdoor workers and athletes exposed to heat combined with exertion
- Individuals taking certain medications that affect fluid balance or heat response
How to prevent heat stroke
Stay hydrated: In hot weather, drink water frequently, before you’re thirsty. Avoid alcohol and caffeine, as these can contribute to dehydration.
Wear appropriate clothing: Loose, light-coloured clothing and a hat help heat escape and reflect sunlight.
Keep cool: Seek shade or air-conditioned spaces during severe heat. Take regular breaks if working outdoors.
Plan activities wisely: Avoid strenuous physical activity during the hottest part of the day.
Acclimatise gradually: If you’re not used to hot weather, for example when travelling, allow your body to adapt slowly over several days.
First aid for heat stroke
Heat stroke is a medical emergency, and immediate action makes a critical difference.
Seek urgent medical care
Call the emergency medical services immediately if someone shows heat stroke symptoms.
Cool the casualty down rapidly
While waiting for help to arrive:
- Move the casualty out of direct heat and into the shade or an air-conditioned room.
- Loosen or remove excess clothing.
- Cool their body quickly using cold water immersion if possible (such as a cool shower or bath), or by applying ice packs to their armpits, groin, neck, and back.
- Fan and mist the person to promote evaporative cooling.
Heat stroke cooling must be aggressive because a high core temperature can cause damage to the organs, including the brain, kidneys, and heart.
Hydration and monitoring
If the casualty is conscious and able to drink, get them to sip on cool fluids that contain electrolytes. Do not allow them to drink too quickly as this can cause vomiting. Continue to monitor the casualty’s temperature and mental status until paramedics or medical professionals arrive.
What happens if heat stroke is left untreated?
Left untreated, heat stroke can lead to dehydration, brain damage, organ failure, or death. Prompt treatment and first aid in the form of cooling and summoning the emergency services care dramatically reduce these risks.
Heat stroke is preventable: Take care in hot weather
Heat stroke is preventable when you understand the risks and take sensible precautions during hot weather or intense physical activity. Look out for early warning signs, stay hydrated, and administer first aid in the form of cooling measures as soon as symptoms of heat stroke appear. Your body’s cooling system is effective, but it can be overwhelmed. Recognising when it’s failing is key to staying safe in the heat.