Heat Stroke: Causes, Symptoms and Treatment

Every summer, as temperatures rise across the UK and abroad, heat-related illness makes its way into the headlines. Yet despite the coverage, many people still struggle to recognise the warning signs or know what to do when things turn serious. Heat stroke is one of those conditions where time matters.

In this guide, we’ll walk you through everything you need to know: what heat stroke actually is, how to spot it, how it’s treated, and most importantly how to avoid it in the first place. Whether you’re planning a holiday abroad or simply enjoying the UK summer, we hope you’ll find this useful.

What is Heat Stroke?

Heat stroke is a severe and potentially life-threatening condition that occurs when the body’s core temperature rises to 40°C (104°F) or above, and the normal mechanisms for regulating that temperature stop working properly. Unlike heat exhaustion, which is uncomfortable and unpleasant but usually manageable, heat stroke is a medical emergency and it requires urgent treatment.

The body is remarkably good at keeping itself cool. Sweating, increased blood flow to the skin, and slowing down physical activity are all part of that process. But when those mechanisms are overwhelmed by extreme heat, high humidity, physical exertion, or a combination of all three, core temperature can spiral upward rapidly and can quickly damage the brain, heart and kidneys.

Heat Stroke vs Sun Stroke: Are They the Same?

This is a question I get asked regularly, and the short answer is: yes, they’re effectively the same condition. ‘Sun stroke’ is the more colloquial term, often used when heat stroke is triggered specifically by direct sun exposure.

Medically, we call it heat stroke. There is one useful distinction worth knowing: heat stroke can happen even without direct sunlight. Spending time in a very hot, poorly ventilated room, or exercising hard in humid conditions can trigger it just as easily. While you might associate this condition with holidays in Spain or Greece, it can and does happen right here in the UK, particularly during heatwaves.

Heat Stroke Symptoms

Recognising heat stroke quickly can make a real difference to outcomes. The symptoms can come on fast, and some of them particularly the neurological signs — distinguish it clearly from the milder heat exhaustion.

• Core body temperature of 40°C or above

• Hot, red skin that may be dry (lack of sweating is a warning sign - see FAQ below)

• Confusion, disorientation or strange behaviour

• Slurred speech

• Loss of coordination or unsteadiness on their feet

• Severe headache

• Nausea or vomiting

• Rapid, strong heartbeat

• Seizures

• Loss of consciousness or collapse

How Quickly Can Heat Stroke Become Life-Threatening?

Very quickly. Without treatment, organ damage can begin within minutes of core temperature reaching critical levels. This is not a condition where you can wait and see. If you suspect someone has heat stroke, call 999 immediately.

While waiting for the ambulance:

• Move them to a cool, shaded area immediately

• Remove unnecessary clothing

• Cool them down as rapidly as possible — apply cold, wet towels or cloths to the skin, particularly the neck, armpits and groin where blood vessels are close to the surface

• If you have access to a cold water bath or shower, use it

• Fan them to encourage evaporation and heat loss

• Do not give them anything to drink if they are confused or unconscious

  
  

How To Treat Heat Stroke

In hospital, our priority is getting their temperature down quickly. Here’s what we do:

• Immerse the patient in ice-cold water or apply ice packs 

• Give intravenous (IV) fluids to rehydrate and support blood pressure

• Monitor and treat for any organ complications (such as kidney or heart involvement)

• Use medications to control seizures if needed

• Give oxygen

  
  

How Long Does Heat Stroke Last?

With prompt treatment, the acute phase the period of dangerously elevated temperature can be brought under control within hours. However, the effects on the body can linger considerably longer. Without treatment, heat stroke can cause permanent neurological damage or be fatal.

Severity matters here too. Mild cases treated quickly may resolve in a day or two. More severe episodes, particularly where there has been organ involvement, can result in a hospital stay of several days.

How Long Does It Take To Recover From Heat Stroke?

Recovery varies significantly from person to person and depends on how quickly treatment was received and whether any organs were affected. Most people who receive timely hospital care make a good recovery over days to weeks. Fatigue, headaches and difficulty concentrating can persist for some time after the acute episode.

One thing worth knowing: once you’ve had heat stroke, you may be more vulnerable to heat for a period afterwards. Take things gently and avoid heat exposure while you’re recovering.

How To Prevent Heat Stroke

The good news is that heat stroke is mostly preventable. Here’s what you can do:

• Stay well hydrated - drink cool, non-alcoholic fluids throughout the day, even if you don’t feel thirsty

• Avoid being outdoors in direct sun between 11am and 3pm when UV and heat are at their peak

• Wear loose, light-coloured clothing

• Seek shade or air-conditioned spaces during the hottest parts of the day

• Avoid excessive alcohol and caffeine, both of which speed up dehydration

• Never leave children or vulnerable adults in parked cars

• Keep rooms cool by drawing curtains on sun-facing windows; open windows at opposite ends of a room to create airflow

• If using a fan, place it lower in the room and consider putting ice or a cool wet cloth in front of it to help cool the air

How To Protect Your Skin From Sun Damage

Looking after your skin in the sun and protecting yourself from heat stroke are two sides of the same coin. Sun damage adds up even on days when you don’t feel burned, and it's linked to your risk of heat stroke too

• Apply a broad-spectrum sunscreen of at least SPF 30 generously and often, especially after swimming or sweating

• Cover up with lightweight, long-sleeved clothing and a wide-brimmed hat

• Protect your eyes with UV-rated sunglasses

• Moisturise after sun exposure to support your skin’s outer barrier

• Stay in the shade, especially between 11am and 3pm

The more time you spend in direct sun, the greater your risk of both sunburn and heat stroke. 

Heatwaves In The UK

There’s a temptation to assume that heat stroke is something that happens on holiday, in countries where temperatures regularly top 40°C. But the UK has experienced a notable increase in significant heatwaves in recent years, and with climate change projections pointing toward hotter and more frequent summers, this is a growing concern.

A heatwave is officially declared when an area reaches a certain temperature threshold for three or more consecutive days the threshold varies from 25°C to 28°C depending on region. In summer 2022, parts of the UK recorded temperatures above 40°C for the first time in recorded history.

The UKHSA and the Met Office jointly operate a weather health alerting system that issues colour-coded warnings during periods of extreme heat. Even a yellow alert, the lowest tier signals meaningful health risk, particularly for vulnerable groups.

Who Is Most Vulnerable During a Heatwave?

While heat stroke can affect anyone, some groups are at significantly higher risk:

• Children under five years old, whose bodies heat up more quickly and cannot always communicate how they feel

• Adults aged 65 and over, whose thermoregulation is less efficient

• People with chronic health conditions, including cardiovascular disease, diabetes and kidney disease

• Those taking certain medications, including diuretics, blood pressure medications and some psychiatric drugs

• Pregnant women

• People with learning disabilities or limited mobility are also at greater risk, as they may not recognise symptoms or be able to move somewhere cooler

How Long Does a Heatwave Usually Last?

UK heatwaves typically last anywhere from two or three days to around two weeks, though they can extend further. The duration varies by region, with southern England generally experiencing longer spells. What’s important to understand is that sustained heat, even at temperatures many countries would consider moderate is particularly challenging for a population and built environment not designed for it. UK homes, for example, are built to retain heat rather than release it, which means indoor temperatures can remain dangerously high long after outdoor temperatures have started to drop.

Conclusion

An awareness of heat stroke is something we all need to be aware of not just when we’re on a sun-soaked beach abroad but right here at home. Knowing the signs and acting quickly can save lives.

If you’re heading abroad this year, don’t forget that travel health preparation goes well beyond heat awareness. Different climates bring different health risks, from tropical infections to altitude sickness. Our team at Health Klinix can help you get travel-ready with expert advice and any vaccinations you might need. You can view our full range of travel vaccination services or book a consultation online at a time that suits you - by phone, video, or in person.

Stay cool, stay hydrated, and look out for those around you.

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Frequently Asked Questions

How can I tell the difference between heat exhaustion and heat stroke?

Heat exhaustion is the warning stage. Your symptoms may include heavy sweating, nausea, dizziness, headache, muscle cramps and feeling faint - but you’ll still be alert and responsive. If you’re able to move to a cool place, rest and rehydrate, you should recover within 30 minutes without needing emergency treatment.

Heat stroke is what happens when those cooling measures don’t work, or aren’t applied in time. The key differences are a very high body temperature (40°C or above), neurological symptoms like confusion, slurred speech or loss of consciousness, and the potential for serious organ damage. If you’re uncertain which you’re dealing with, treat it as heat stroke and call 999.

What are the first signs of heat exhaustion?

The earliest signs to look out for are heavy sweating, pale and clammy skin, feeling dizzy or faint, nausea, and a headache. You might also notice a fast but weak pulse, and muscle cramps, particularly in the legs. Thirst is another early indicator that the body is losing fluid faster than it’s taking it in.

Is a lack of sweating a definitive sign of heat stroke?

Not always, but it’s an important one. Classic heat stroke (triggered by environmental heat, particularly in elderly or vulnerable people) often presents with hot, dry skin because the sweating mechanism has failed. However, exertional heat stroke (the kind that comes on during intense physical activity) can still involve sweating. So while absent sweating in a hot environment should raise serious concern, the presence of sweating doesn’t rule heat stroke out.

Can the heat cause diarrhoea?

Yes, it can although it’s not usually one of the first symptoms people think of. Heat and dehydration can affect gut function and motility. Nausea, vomiting and diarrhoea can all occur as part of heat-related illness. Diarrhoea in hot weather means you can lose even more fluids and electrolytes, which in turn worsens dehydration. It’s another reason to stay well hydrated and seek help if symptoms worsen.

How do I know if I have heat stroke?

If you’re wondering about this and you’re in a hot environment, the safest thing to do is act as if you might. Move somewhere cool, stop all physical activity, and try to cool yourself down. The distinguishing features of heat stroke high temperature, confusion, not sweating, skin that’s hot and red (not always easy to see with dark skin) are often more obvious to those around you than they are to you. If someone around you seems confused, disorientated or is not responding normally in a hot environment, call 999 without delay.

Is heat stroke a medical emergency?

Yes, without question. Heat stroke is a medical emergency that requires an ambulance and hospital treatment. Don’t try to manage it at home. Call 999 immediately while taking steps to cool the person down. The faster treatment begins, the better the outcome.

References

1. NHS. Heat exhaustion and heatstroke. Available at: https://www.nhs.uk/conditions/heat-exhaustion-heatstroke/ [Accessed June 2026]

2. UK Health Security Agency. Weather health alerting system. Available at: https://ukhsa-dashboard.data.gov.uk/weather-health-alerts/heat [Accessed June 2026]

3. Health Klinix. Sun Safety: How to Protect Your Skin This Summer. Available at: https://www.healthklinix.co.uk/post/sun-safety-how-to-protect-your-skin-this-summer [Published August 2024]

4. World Health Organization. Heat and health. Available at: https://www.who.int/news-room/fact-sheets/detail/climate-change-heat-and-health [Accessed June 2026]

Reviewed and approved by:

Dr Ravi Gowda, Consultant in Infectious Diseases and Travel Medicine

MBBS, MRCP(UK), DTM&H, MRCGP, DCH, DRCOG, DFFP