Heat Exhaustion vs Heatstroke: NHS First Aid Signs and Treatment (UK 2026)

Recognising the difference between heat exhaustion and heatstroke could save a life this summer.

Britain’s May 2026 heatwave has been extraordinary. The Met Office recorded 35°C on 26 May — the hottest day of the year so far — and broke May temperature records multiple times in a single week. On the bank holiday Monday, NHS England logged 20,092 visits to its heatstroke advice page, compared with just 488 the previous Monday. Visits to baby first aid and sun safety pages jumped almost 3,500 per cent.

With the Met Office’s early June outlook showing temperatures slightly above average but uncertainty about further hot spells, knowing the difference between heat exhaustion and heatstroke could matter this summer. This article gives you the precise NHS distinction, a clear step-by-step first aid guide from the British Red Cross and St John Ambulance, the 30-minute rule that tells you when to call 999, and who faces the greatest risk.

Heat exhaustion versus heatstroke — the NHS definition

Understanding the difference starts with one idea: control. Heat exhaustion is what happens when your body is overheating but still managing its own temperature. You’re losing water and salt faster than you can replace them, and your body is sounding an alarm — heavy sweating, dizziness, cramps. But your internal thermostat is still working. According to NHS guidance, this is the early warning stage, and it’s something you can usually manage at home with cooling, rest and fluids.

Heatstroke is a different situation entirely. Your body’s cooling system has failed. Core temperature climbs to 40°C or higher, sweating may stop, and your brain begins to be affected — confusion, slurred speech, even seizures. The British Red Cross describes heatstroke as a genuine medical emergency where every minute of delay increases the risk of organ damage and death.

Here’s the critical point the NHS stresses: if heat exhaustion is not spotted and managed within roughly 30 minutes, it can progress to heatstroke. That 30-minute window is the dividing line between a problem you can solve with a cold flannel and a bottle of water, and a 999 call. Both the NHS and the British Red Cross use this rule as their benchmark, and it’s the single most important thing to remember if you see someone struggling in the heat this summer.

How to spot it — signs in adults, children and the elderly

Recognising heat exhaustion early gives you the best chance of stopping it before it becomes dangerous. NHS guidance lists the following signs in adults: tiredness, weakness, a headache, feeling dizzy or faint, heavy sweating with pale and clammy skin, cramps in the arms, legs or stomach, a fast pulse and fast breathing, a high temperature that’s usually below 40°C, intense thirst, and nausea or vomiting. St John Ambulance emphasises that the combination of heavy sweating and pale, clammy skin is the hallmark — it’s what distinguishes heat exhaustion from heatstroke at a glance.

Children can present differently. A heat-exhausted child may appear tired, drowsy, floppy or unusually irritable. Babies may produce fewer wet nappies than normal. Behaviour change — a child who’s gone quiet, or an older person who seems confused — is often the first visible clue, and it’s one that family members and carers are best placed to notice.

Now for the heatstroke red flags the NHS wants you to act on immediately. Skin that’s hot to the touch but no longer sweating — or that looks red and dry. Confusion, slurred speech, irrational behaviour. Seizures. Loss of consciousness. Rapid, shallow breathing. A core body temperature of 40°C or higher. And critically, no improvement after 30 minutes of active cooling and rest. British Red Cross and St John Ambulance training both stress that the absence of sweating in someone who was previously drenched is one of the most reliable warning signs. In the elderly and people with dementia, a change in behaviour or increasing confusion may be the only obvious signal. Trust your instincts — if someone looks wrong in the heat, act.

Having the right supplies to hand makes a real difference when temperatures spike.

First aid step by step — heat exhaustion

If you’ve identified heat exhaustion, the British Red Cross and NHS recommend the following sequence. Each step builds on the one before it, and all five should be completed together for the best outcome.

First aid step by step — heatstroke

Call 999 immediately. Do not wait to see if things improve. While you’re waiting for the ambulance, move the person to the coolest place available and remove their outer clothing. Wrap them in a cool, wet sheet if you have one; if not, fan them and sponge their skin with cool water, concentrating on the neck, armpits and groin. Apply cold packs wrapped in cloth to those same areas.

Keep checking their breathing and their level of response throughout. If they lose consciousness but are still breathing, put them in the recovery position. If they stop breathing, start CPR if you’re trained to do so. One key rule from NHS and British Red Cross guidance: do not give a confused, drowsy or unconscious person anything to drink. The risk of choking — aspiration — is real and serious.

Faster cooling improves survival rates. That cooling-while-you-wait window before the ambulance arrives is not passive time. It’s active treatment, and it matters enormously.

Who is at higher risk — and how to keep them safe

Certain groups face a much greater danger during hot weather. Practical UK steps from UKHSA and NHS advice include staying out of direct sun between 11am and 3pm, wearing loose light-coloured cotton clothing and a wide-brimmed hat, and sipping water steadily throughout the day rather than drinking large amounts at once. Keep curtains and blinds closed in south-facing rooms during daylight hours. Never leave babies, children or pets in a parked car — interior temperatures can exceed 50°C within minutes. Check on elderly neighbours and relatives regularly; heatwave deaths in the UK are disproportionately concentrated among older people living alone.

Look up the UKHSA Heat-Health Alert level for your region on the gov.uk website — these alerts are now the official trigger for NHS and adult social care services to take preventive action.

Frequently Asked Questions

What is the difference between heat exhaustion and heatstroke?

Heat exhaustion is your body overheating but still controlling its temperature — you’ll sweat heavily, feel dizzy, get a headache and possibly cramp. Heatstroke means your cooling system has failed: your temperature hits 40°C or above, sweating may stop, and confusion or seizures can follow. Heat exhaustion is manageable at home. Heatstroke is a medical emergency requiring a 999 call.

When should I call 999 for someone in the heat?

Call 999 if the person shows signs of heatstroke — hot dry skin, confusion, slurred speech, seizures, loss of consciousness, or a temperature of 40°C or above. Also call 999 if someone with heat exhaustion has not improved after 30 minutes of active cooling, rest and fluids. Don’t wait for every red flag to appear; one or two are enough.

How do I cool someone down quickly with things I have at home?

Spray or sponge their skin with cool water from the tap. Fan them while you do it — anything that moves air across wet skin helps. Wrap a bag of frozen peas or ice cubes in a tea towel and press it against their neck, armpits and groin. A damp bed sheet draped over them works well for heatstroke. A paddling pool or cool shower is fine for someone who’s still alert and standing.

How long should heat exhaustion last before I worry?

Around 30 minutes. If you’ve moved someone to a cool place, cooled their skin and given them fluids, they should start feeling better within half an hour. No improvement after 30 minutes — or any worsening — means you should treat it as heatstroke and call 999 immediately.

Can children get heatstroke faster than adults?

Yes. Children’s bodies generate more heat relative to their size and sweat less efficiently, which means their core temperature can rise more quickly. Babies are especially vulnerable because they can’t tell you they’re thirsty or too hot. Watch for drowsiness, floppiness, irritability, fewer wet nappies and any change in normal behaviour.

Heat exhaustion presents with pale, clammy, heavily sweating skin, dizziness and headache. Cool the person, sit them down, give small sips of water and raise their legs slightly. They should improve within 30 minutes. Heatstroke brings hot dry skin, confusion, a temperature above 40°C and a body that’s stopped sweating. That’s a 999 call — no hesitation. Keep cooling them while you wait for help.

The 30-minute rule is the line between managing a problem at home and a genuine emergency. During a heatwave, check the UKHSA Heat-Health Alert level for your region on gov.uk, and keep an eye on anyone around you who might not recognise the signs themselves. For more guidance, read our UK first heatwave 2026 amber alert NHS guide and sunscreen SPF 50 NHS guidance for children.