Heat Stroke vs Heat Exhaustion
Heat exhaustion and heat stroke look alike from the outside and are treated completely differently. One is managed where the person is standing. The other is a life-threatening emergency where minutes of delay cause permanent harm.
The sign that separates them is altered mental state — confusion, slurred speech, unsteadiness, strange behaviour, collapse. If the brain is affected, it is heat stroke and it is an ambulance.
The emergency numbers in this guide are Australian. If you are somewhere else, call your own country’s emergency number instead — 911 in the United States and Canada, 999 in the United Kingdom, 112 across Europe and on most mobile phones worldwide. The advice itself applies wherever you are.
The 10-minute version
- Confusion, slurred speech, unsteadiness or collapse = heat stroke = call 000 immediately. Do not wait to see if it improves.
- Cool aggressively. For anyone over five, whole-body immersion in cold water, neck down, for 15 minutes is the most effective method. A bath, as cold as you can make it.
- Only give fluids if the person is fully conscious and able to swallow. Someone confused or drowsy must not be given a drink.
Telling them apart
| Heat exhaustion | Heat stroke | |
|---|---|---|
| Mental state | Normal, though tired and miserable | Confused, slurred, unsteady, aggressive, seizing or unconscious |
| Skin | Pale, clammy, sweating heavily | Hot; may be dry or still sweaty |
| Other signs | Weakness, dizziness, headache, nausea, cramps, fast pulse | Very high body temperature, rapid breathing, vomiting |
| Response | Improves within about 30 minutes of cooling and rest | Does not improve. Deteriorates |
| What to do | Cool, rest, sip fluids | 000 immediately and cool aggressively while waiting |
Two myths worth killing:
“Heat stroke skin is always hot and dry.” Not reliably. Someone can be sweating and still be in heat stroke, particularly with exertional heat stroke in a fit young person. Do not use dry skin as your test — use mental state.
“They just need to sit down and have a drink.” For heat exhaustion, largely true. For heat stroke, dangerously wrong, and giving fluids to someone who is not fully alert risks choking.
Heat exhaustion: what to do
- Move them somewhere cool — shade, air conditioning, a cool room.
- Lie them down and raise the legs slightly.
- Remove excess clothing.
- Cool the skin: wet cloths, a spray bottle, a fan, cool water over the skin.
- Sips of cool water if they are fully conscious. For exertional dehydration, a carbohydrate-electrolyte drink of the kind sold as a sports drink is reasonable.
- Watch them for 30 minutes. If they are not clearly improving, or if mental state changes at any point, call 000.
Heat stroke: what to do
Call 000 first, or have someone else call while you start cooling. ANZCOR advises sending for an ambulance early.
Then cool, and cool properly. The evidence favours aggressive cooling:
- Whole-body cold water immersion, neck down, for 15 minutes, for anyone over five years of age. A bath filled with cold water is the most effective option available in a house.
- If immersion is not possible: wet them continuously with cold water under a shower or with a hose, apply ice packs to the groin, armpits, cheeks, palms and soles, and keep re-wetting the skin with a cloth or spray.
- Keep the airway in view. Consciousness can deteriorate, and someone in a bath who becomes unresponsive must be got out immediately.
- Do not give fluids to anyone who is not fully conscious and able to swallow.
- Do not use alcohol rubs, and do not pack in ice unattended.
- Keep cooling until the ambulance arrives or until they are clearly improving and instructed otherwise.
Those specific ice-pack sites are not arbitrary — they sit over large blood vessels close to the surface, which is why they shed heat faster than ice on the forehead.
Who is at risk
- Anyone exercising or working in heat, particularly if unacclimatised
- Older adults, especially living alone — Australian coronial data shows most indoor heat deaths are in people over 60
- Babies and young children
- Anyone with a chronic illness — heart, lung, kidney, diabetes
- People on medications affecting fluid balance or sweating
- Anyone in a hot car. Never leave a child or animal in one, even briefly
What actually goes wrong
Mental state is not checked. It is the only sign that reliably separates the two conditions.
Cooling is too timid. A damp flannel is not treatment for heat stroke. Cold immersion is.
Fluids are given to someone who is confused.
The ambulance is called late, after “seeing if they come round”.
Dry skin is used as the test, missing heat stroke in someone still sweating.
They are left alone to rest and deteriorate unobserved.
Exercise resumes the same day after heat exhaustion. It should not.
Thresholds
| Situation | The rule |
|---|---|
| Any altered mental state in heat | Heat stroke. Call 000 now |
| Cooling, over 5 years old | Cold water immersion, neck down, 15 minutes |
| No bath available | Shower or hose continuously, ice packs to groin, armpits, cheeks, palms, soles |
| Fluids | Only if fully conscious and able to swallow |
| Heat exhaustion not improving in 30 minutes | Escalate. Call for medical advice |
| Anyone found collapsed in a hot room | 000, cool aggressively, check breathing |
| After heat exhaustion | No further activity that day. Fluids, rest, shade |
What it costs
| Tier | Spend | What it buys |
|---|---|---|
| Free | $0 | Knowing that mental state is the test, and that a cold bath is the treatment. Both are the whole article |
| Solid | ~$30–60 | A spray bottle, several reusable ice packs, an indoor thermometer, oral rehydration sachets |
| Better | ~$150–250 | A hands-on first aid course, which covers this alongside CPR and bleeding |
The drill: the summer briefing
Five minutes, once, at the start of summer, out loud with whoever you live with.
- Say the test: “Confused, slurred, unsteady or collapsed means 000.”
- Point at the bath. That is your cooling equipment. Confirm it fills reasonably fast.
- Put ice packs in the freezer and say where they are.
- Agree who calls 000 and who starts cooling, so both happen at once.
- Name the vulnerable people you will check on in person, and when.
Frequently asked questions
What is the difference between heat exhaustion and heat stroke?
Mental state. Heat exhaustion involves heavy sweating, weakness, dizziness and nausea with normal thinking, and improves within about 30 minutes of cooling. Heat stroke involves confusion, slurred speech, unsteadiness, seizures or unconsciousness, and is a life-threatening emergency requiring 000.
How do you cool someone with heat stroke?
For anyone over five, immerse them in cold water from the neck down for about 15 minutes — a bath as cold as possible is the most effective method. If that is not available, wet them continuously with a shower or hose and apply ice packs to the groin, armpits, cheeks, palms and soles.
Should I give someone with heat stroke water?
Only if they are fully conscious and able to swallow. Someone confused, drowsy or unresponsive must not be given fluids because of the choking risk.
Is heat stroke skin always hot and dry?
No. Someone can still be sweating and be in heat stroke, especially with exertional heat stroke. Use altered mental state as the test, not skin condition.
When should I call an ambulance?
Immediately, for any altered mental state in a hot person. ANZCOR advises sending for an ambulance early in heat-induced illness, and also call if heat exhaustion is not clearly improving within 30 minutes.
Can someone go back to work or exercise after heat exhaustion?
Not the same day. They need rest, shade and fluids, and they remain at increased risk for the rest of the day.