Heat stroke symptoms vs heat exhaustion: signs and first aid

Heat stroke symptoms are a very high body temperature, usually 40 °C (104 °F) or more, hot and red skin, confusion, a pounding headache, dizziness and, in severe cases, seizures or loss of consciousness. Heat stroke is a medical emergency: the body can no longer cool itself, and without fast help it can damage the brain, heart and kidneys.

If you suspect heat stroke, call 911 in the US and Canada, 999 in the UK, 112 in the EU or 000 in Australia, and start cooling the person while help is on the way. This article gives general guidance and does not replace care from a health professional.

Key takeaways

• Heat stroke is an emergency: core body temperature rises above about 40 °C (104 °F) and the brain is affected, causing confusion, collapse or seizures. The CDC lists a temperature of 103 °F (39.4 °C) or higher as a warning sign.
• Heat exhaustion is the earlier, milder stage: heavy sweating, cold and clammy skin, weakness, dizziness and nausea, with a clear mind.
• While waiting for help, move the person to shade, remove extra clothing and cool them fast with water and moving air; cold water immersion works best.
• Most at risk: adults over 65, babies and young children, people with chronic illness, and anyone working or exercising in the heat.
• Never leave a child, a vulnerable adult or a pet in a parked car: in one study the inside warmed by an average of 19 °F (about 11 °C) in 10 minutes.

What is heat stroke?

Heat stroke is the failure of the body's temperature control: the body builds up more heat than it can get rid of and its core temperature climbs above about 40 °C (104 °F). From that point the organs start to suffer, and the brain is the first to show it.

Your body cools mainly by sweating and sending blood to the skin. When the air is very hot, humidity stops sweat from evaporating, or you are dehydrated, that system fails. That is why 93 °F (34 °C) with very humid air can be as dangerous as 104 °F (40 °C) in dry air, something the heat index in our guide to the feels like temperature captures.

There are two main forms. Classic heat stroke mostly affects older or sick people during a heat wave, often at home over several days. Exertional heat stroke strikes healthy people exercising or working hard in the heat, sometimes within an hour.

Heat exhaustion vs heat stroke: what is the difference?

The key difference is mental state and temperature: with heat exhaustion the person stays alert and makes sense, while with heat stroke they become confused, behave oddly or lose consciousness. Heat exhaustion can turn into heat stroke if nothing is done. Heat cramps are the mildest heat illness: painful muscle spasms during heavy sweating and exercise.

	Heat cramps	Heat exhaustion	Heat stroke
Body temperature	Normal	Normal or slightly raised	About 40 °C (104 °F) or higher
Skin	Sweaty	Cold, pale and clammy	Hot and red; dry, or damp after exertion
Pulse	Normal	Fast and weak	Fast and strong
Mental state	Alert	Alert, may feel faint	Confused, agitated, slurred speech, collapse, seizures
Other signs	Muscle pain or spasms	Heavy sweating, thirst, tiredness, dizziness, nausea, headache	Headache, nausea or vomiting, fast breathing
What to do	Stop, rest in the shade, drink water	Cool down, sip water; get medical help if vomiting or not better within an hour	Call the emergency number and cool immediately

Heat stroke symptoms in adults, kids and older people

The symptoms of heat stroke are similar at any age, but each group has its own warning signs.

Heat stroke symptoms in adults

In an adult, the alarm signs are a very high temperature, hot skin, a severe headache, dizziness, nausea or vomiting, a racing pulse and, above all, any change in behavior: talking nonsense, disorientation, stumbling or sudden irritability. In exertional heat stroke the person may still be sweating, so damp skin does not rule it out.

Heat stroke symptoms in kids and babies

Children heat up faster than adults and rely on others for drinks. In babies, watch for irritability or constant crying, unusual sleepiness, very hot skin, a dry mouth, dry diapers for hours or a sunken soft spot on the head. In older children, act on extreme tiredness, headache or vomiting after playing in the sun.

Heat stroke symptoms in older people

Older adults feel less thirsty, sweat less and often take medicines that affect temperature control, such as some diuretics. In them, heat stroke can be subtle: weakness, confusion, apathy or a fall. Call or visit older relatives every day during a heat wave.

Can heat stroke symptoms show up the next day?

Heat stroke develops during or soon after heat exposure, not out of the blue a day later. Classic heat stroke can build up over several hot days, and after any heat illness you may feel tired, achy or unwell for a day or more. If someone is confused, vomiting or getting worse after a hot day, treat it as urgent and get medical help.

Heat stroke treatment: first aid while you wait for help

The first step is to call the emergency number; the second is to cool the person as fast as possible, because every minute counts. Follow these steps:

1. Call 911, 999, 112 or 000 and say you suspect heat stroke.
2. Move the person to shade or somewhere cool, ideally air-conditioned.
3. Remove tight or extra clothing.
4. Cool the body fast: the most effective method is immersing the body up to the neck in cold water, such as a tub of water and ice. If that is not possible, soak the skin with cool water using a hose, shower or wet towels, and fan hard so the water evaporates.
5. Put cold packs on the neck, armpits and groin, wrapped in a cloth.
6. If they are awake and can swallow, give sips of cool water; if confused or vomiting, give nothing by mouth.
7. If they lose consciousness but are breathing, place them on their side in the recovery position and watch their breathing until help arrives.

Do not give alcohol or caffeine. Fever medicines such as acetaminophen (paracetamol) or ibuprofen do not lower body temperature in heat stroke, because it is not a fever caused by infection; only physical cooling works.

Where trained staff and a cold water tub are on site, as at many sports events, the National Athletic Trainers' Association advises "cool first, transport second".

How to prevent heat stroke

The most effective way to prevent heat stroke is to avoid sun and hard effort in the hottest hours, drink water often and keep your home cool. Heat alerts help you know when to take extra care: in the US, the National Weather Service issues Heat Advisories and, since March 2025, Extreme Heat Warnings, which replaced the old Excessive Heat Warnings. In England, the UK Health Security Agency issues yellow, amber and red heat-health alerts from June 1 to September 30.

• Drink water regularly, even if you are not thirsty, and limit alcohol.
• Avoid sun and exercise in the middle of the day, and wear light, loose, light-colored clothing and a hat.
• Keep your home cool: close blinds during the day and open windows at night, when it is cooler outside.
• Go somewhere cool if your home overheats, such as a library, a mall or a cooling center.
• Never leave anyone in a parked car: the temperature inside climbs fast even with the windows cracked.
• Protect yourself from the sun's rays too: the UV index is often very high on the hottest days.

Heat stroke in dogs: signs and first aid

Dogs get heat stroke more easily than people, because they barely sweat and cool themselves mainly by panting. Flat-faced breeds such as bulldogs, pugs and boxers, puppies, older dogs and overweight dogs are the most vulnerable.

Warning signs are heavy panting, drooling, very red or bluish gums, weakness, vomiting, stumbling and, in severe cases, collapse. Move the dog to shade, wet it with cool, not ice-cold, water on the neck, belly and paws, let air flow over it, and go to a vet straight away, keeping it cool on the way.

To prevent it, walk your dog early and late, avoid hot pavement and never leave it in the car.

How to use Clima de Hoy to avoid dangerous heat

Clima de Hoy shows the temperature, feels like temperature and UV index hour by hour for each city, so you can pick the safest time to go out or train.

In summer, check the hourly forecast for Seville, one of Europe's hottest cities, to see when the heat eases, and the 7 day forecast for Miami to know how long a hot, humid spell will last. Humidity matters as much as heat: our guide to relative humidity explains why.

Frequently asked questions

What are the first signs of heat stroke?

The first signs are usually those of heat exhaustion: heavy sweating, strong thirst, tiredness, dizziness, headache and nausea. If hot skin, confusion or disorientation follow, it has become heat stroke and you should call 911, 999, 112 or 000 straight away.

How long does it take for heat stroke to develop?

It depends on the type. Exertional heat stroke can come on within an hour or less during hard exercise in the heat, while classic heat stroke builds up over several hot days, especially in older people living in very hot homes.

How do you bring down the temperature of someone with heat stroke?

With physical cooling: move them to shade, remove clothing and, best of all, immerse them in cold water up to the neck. Otherwise, soak their skin with cool water, fan them and put cold packs on the neck, armpits and groin. Do this while waiting for emergency services, not instead of calling them.

Can heat stroke cause lasting damage?

Yes. Severe heat stroke can damage the brain, heart, kidneys and liver, and it can be fatal. How quickly the person is cooled and treated is what most affects recovery.

Are children at higher risk of heat stroke?

Yes, especially babies and young children, because they heat up faster and depend on an adult for drinks and shade. Offer them water often, avoid the middle of the day and never leave them in a parked car, even for a few minutes.