Signs of Heat Exhaustion and Heat Stroke to Watch For in 2026

Heat exhaustion and heat stroke both come from the body overheating, and the difference between them matters enormously. Heat exhaustion means your body has lost too much water and salt through sweat but can still cool itself; heat stroke means that cooling system has failed, core temperature has climbed to 104°F (40°C) or higher, and the brain and organs are being damaged. Knowing the signs of heat exhaustion and heat stroke, especially the difference in mental status, tells you whether someone needs a glass of water and shade or an ambulance.

Most heat illnesses happen on ordinary days: a walk at noon, a hard shift on a roof, a car that sat in the sun. By the time someone looks obviously unwell, the useful window for easy intervention has often already closed, which is why it helps to know the early picture rather than the dramatic one.

This is general information about heat illness, not medical advice. If you are worried about someone right now, call your local emergency number, and for anything about your own health, speak to a doctor.

What Are Heat Exhaustion and Heat Stroke?

Heat exhaustion is what happens when a body working hard in hot conditions loses more water and salt through sweating than it replaces. Sweat still works, so the body keeps trying to cool itself, but blood flow shifts away from the skin and digestive system to support the brain and muscles.

Left untreated, it can progress to heat stroke. That happens when thermoregulation fails completely: the body can no longer produce enough sweat to cool itself, core temperature climbs, and heat begins damaging the brain, kidneys and other organs. Heat stroke is a life-threatening medical emergency that can kill within hours.

There is also a milder stage between them. Heat cramps and heavy sweating with weakness are dehydration signs, and severe dehydration alone can make someone collapse without the core temperature reaching heat stroke levels.

Public health bodies such as the CDC and the UK Health Security Agency treat heat exhaustion as something you catch early, cool down and recover from, and heat stroke as something you call emergency services for. Both use the same core message, and neither treats them as interchangeable.

Signs of Heat Exhaustion and Heat Stroke to Watch For

The clearest early signs of heat exhaustion are heavy sweating, a cool or clammy feel to the skin, and a general look of having overheated. Knowing the heat stroke warning signs matters more, because those mean the situation has already passed the point of home first aid.

Common heat exhaustion signs

• Heavy sweating, sometimes soaking through clothing
• Cool, pale, clammy skin that may look flushed
• A weak, fast pulse and fast, shallow breathing
• Intense thirst, dry mouth, dark or very little urine
• Headache, dizziness, or feeling faint when standing up
• Muscle cramps in the legs, arms or abdomen
• Nausea, sometimes vomiting
• Tiredness, weakness and heavy fatigue
• Irritability or restlessness in children

Heat exhaustion is uncomfortable and potentially dangerous, but the person is usually still thinking clearly. They can tell you what is wrong and answer a direct question sensibly.

Heat stroke warning signs

• Confusion, disorientation or slurred speech
• Agitation, aggression or unusual behaviour
• Very hot skin that may be dry, or still sweating heavily
• Core temperature of 104°F (40°C) or higher
• Fainting, loss of consciousness or not responding
• Seizures or convulsions
• Rapid, strong pulse and rapid breathing
• Severe throbbing headache with vomiting
• Loss of coordination, stumbling or inability to walk straight

One correction worth making, because it causes real confusion: heat stroke does not require dry skin. A person can sweat heavily right up to the point of collapse, and skin that feels dry may simply be a later sign. Mental state is the more reliable signal.

Signs on darker skin tones

Many symptom lists describe skin as flushed red or pale, which is much harder to spot on brown and Black skin. Useful alternatives to look for instead: skin that feels unusually hot to the touch, skin that looks ashen or grey rather than pink, lips or fingernails that look dull or bluish, and any sudden change in skin tone compared with that person’s normal.

Signs in babies and young children

Children may not describe how they feel, so behaviour is the clue. A flushed, droopy or unusually quiet infant, a child who stops drinking or cries without tears, a change in wet nappies, vomiting after drinking, or a child who seems floppy or unusually irritable after being in the heat all deserve cooling and a call to a doctor. Children have a lower sweat rate than adults and heat up faster in a parked car.

How to Tell Heat Exhaustion From Heat Stroke

Ask one question: can this person think clearly and talk normally? If the answer is no, treat it as heat stroke and call for help.

Sign	Heat exhaustion	Heat stroke
Mental state	Alert but tired, irritable or dizzy	Confused, slurred speech, aggressive, unresponsive
Skin	Cool, pale, clammy, heavy sweating	Hot and flushed, may be dry or still sweating
Core temperature	Usually below 104°F (40°C)	104°F (40°C) or above
Pulse	Fast and weak	Fast and strong, may be very rapid
Breathing	Fast and shallow	Fast, deep or laboured
Headache	Throbbing but mild to moderate	Severe, often with vomiting
Nausea or vomiting	May feel sick, may vomit once	Persistent vomiting, often severe
Muscle cramps	Common, especially in limbs	May stop as muscles seize up
Consciousness	Stays awake	Fainting, seizures or loss of consciousness
What it needs	Shade, cooling, fluids, monitoring	Emergency services and rapid cooling

Do not wait on a thermometer reading to decide. People have died of heat stroke at temperatures below 104°F, and a rectal reading is the only reliable one. A change in behaviour alone is enough reason to act.

What to Do If Someone Shows Signs of Heat Exhaustion

Act quickly and start cooling within minutes.

1. Stop the activity and move them somewhere cool. Get them out of the sun into shade, an air-conditioned room, or a vehicle with air conditioning running.
2. Loosen or remove outer clothing. Take off hats, heavy layers, belts and anything tight around the neck.
3. Cool gradually and steadily. Apply cool, wet cloths to the neck, armpits and groin, where blood vessels sit close to the surface. Fan the skin. Avoid ice applied directly to bare skin.
4. Give fluids only if they are fully alert. Small, frequent sips of cool water or an electrolyte drink. Nothing by mouth if they are drowsy, confused or vomiting repeatedly.
5. Help them lie down and recover. Lying with legs slightly raised eases dizziness. Keep them resting and cool.
6. Keep watching for 30 minutes. NHS guidance says someone with heat exhaustion should feel better within about half an hour. If they do not, or if they get worse, seek medical advice.

Alcohol, very sugary drinks and caffeinated drinks do not help rehydration, and energy drinks can make the dehydration worse. A doctor is the right person to ask about recovery, especially if the person takes regular medication.

Heat Stroke: What to Do in an Emergency

Suspected heat stroke is an ambulance call. Cooling that starts at home has to keep running while you wait.

1. Call your local emergency number immediately. Say suspected heat stroke and that the person is confused or unresponsive. This is not a call to make later once you have checked the symptoms.
2. Move them out of the heat and loosen clothing. Get them into shade or air conditioning if you can do so safely.
3. Cool aggressively and continuously. Use cool or cold water on the skin, fan hard to move air across damp skin, place cold packs at the neck, armpits and groin, or soak clothing with water and leave it on.
4. Do not give anything by mouth. No water, no sports drink, no medication. An altered person cannot swallow safely and may choke.
5. Stay with them and keep cooling until help arrives. If they lose consciousness, place them on their side in the recovery position and keep cooling them.

Two things to avoid: giving fluids to someone who is not fully alert, and assuming they have improved because they stopped sweating or started shivering. Shivering in a hot environment can be a sign the body is shutting down, not a sign of recovery.

People do survive heat stroke, sometimes with a full recovery, but outcomes depend heavily on how fast cooling started. Emergency departments can cool far faster than a home can, which is the whole point of the call.

Who Is Most at Risk During Hot Weather?

Anyone can get heat illness, but some people reach dangerous temperatures sooner and tolerate it worse.

• Babies, young children and older adults. Infants cannot regulate heat well and heat up quickly in vehicles; adults over 65 are less able to sweat effectively and may not feel thirsty until they are already dehydrated.
• People with chronic conditions. Heart disease, diabetes, kidney disease, obesity and circulation problems all reduce the body’s ability to shed heat.
• People taking certain medications. Diuretics, beta blockers, antihistamines and other anticholinergic drugs, some antidepressants and some blood pressure medicines affect sweating, fluid balance or the body’s heat signals. Review these with a doctor or pharmacist before a hot spell rather than during it.
• Pregnancy. Hormonal and circulatory changes make overheating harder to handle.
• Outdoor workers and athletes. Hours of exertion with no shade, often in heavy clothing and safety gear.
• People not yet acclimatised to the heat. A week or two of gradual exposure gives the body time to adjust, and new workers or visitors often skip that ramp-up.
• Anyone without reliable cooling. Top-floor flats without air conditioning, no shade in the garden, or a commute in a parked car that heats up fast.
• People who drink alcohol outdoors. Alcohol increases fluid loss and masks thirst.

It is worth adding a group that health pages rarely mention: people recovering from a previous heat illness. Heat sensitivity can persist for weeks or months after a single episode of heat exhaustion, with symptoms like a resting heart rate that sits high, night-time chills in a warm room, light sensitivity and dizziness on mild exertion. If that is happening, it belongs in a conversation with a doctor rather than something to push through.

How to Prevent Heat Illness in Hot Weather

Prevention is mostly about timing and shade, not just water.

• Move the hardest work earlier. Outdoor work and exercise in the early morning or after sunset beat the middle of the day by a wide margin.
• Build in breaks in shade. Rest periods in a cool place every 30 to 60 minutes during hard activity make a measurable difference for new workers.
• Drink on a schedule. Small amounts regularly through the day work better than trying to catch up at the end. Add electrolytes for long or heavy sessions.
• Wear light, loose, breathable clothing. Natural fabrics reflect heat and let sweat evaporate; dark synthetic layers trap it.
• Cool the body at the neck, armpits and groin. These are the areas where cooling does the most work.
• Check humidity, not just temperature. Sweat cannot evaporate in heavy humidity, so the same air temperature is far more dangerous on a muggy day.
• Never leave anyone in a parked car. A vehicle can heat up dangerously in a very short time, even with a window cracked.
• Check on the vulnerable daily. A quick call to an older neighbour or relative takes two minutes and catches problems early.
• Keep the home cool. Close blinds and curtains during the day, open windows once the outside air cools in the evening, and fan rooms where there is no air conditioning.
• Acclimatise gradually. Give the first week or two of hot weather lighter work and more frequent breaks.

Frequently Asked Questions

What to Do First

Ask whether the person is thinking clearly and talking normally. Clear answers mean shade, cooling, small sips of fluid and a close watch for the next half hour. Confusion, slurred speech, fainting or a seizure means stop, call emergency services and keep cooling until the helpers take over.

Then, once things have settled, talk to a doctor about the person who is most vulnerable in your household, their medications and their plan for the next hot week. That is a far better time to sort it than during a heatwave.