Heat Exhaustion or Heat Stroke: The Dividing Line

If someone is confused, stumbling, or cannot be woken in the heat, call 911 now. Start cooling them while you wait. Do not wait to take a temperature first.

Heat exhaustion is miserable. Heat stroke is a medical emergency that damages organs and kills people. The difference matters more than almost any other distinction on this site, because in Arizona it is a distinction people have to make in their own kitchen several times a summer.

The clearest single dividing line is how the person is thinking. Somebody sweating heavily, weak, nauseated and miserable but oriented is a different situation from somebody confused, agitated or not making sense. Confusion belongs to the emergency.

Call 911 now if

Drawn from the National Library of Medicine’s guidance on heat emergencies:

• Confusion, agitation, seizures, or any change in alertness
• Loss of consciousness, or somebody who cannot be woken properly
• A temperature over 102°F (38.9°C) alongside heat illness signs
• A rapid pulse or rapid breathing
• Anyone who is not improving despite being cooled — or who is getting worse

A temperature above 104°F (40°C) indicates heat stroke, and that is a definition rather than the number to wait for. Do not wait for 104 to call. Over 102 with the signs above is already the call, and confusion is the call regardless of what any thermometer says.

What to do while you wait

Again from the same source: get them somewhere cool, lying down with their feet raised. Apply cold wet cloths or water directly to the skin, and put cold compresses on the neck, groin and armpits — those three places move heat out of the body fastest.

Keep cooling until help arrives. Cooling is the treatment for heat stroke, not a comfort measure, and every minute of it counts.

⚠ A fan stops helping above 90°F, and that is counterintuitive

The CDC is specific about this: use fans only if indoor temperatures are below 90°F. Above 90°F, a fan can increase body temperature.

That matters here more than almost anywhere. An Arizona house during a power cut or an air-conditioning failure passes 90°F indoors quickly, and “put a fan on them” is exactly what most people would do. Above that line you are moving hot air over hot skin.

Cool water and cold compresses, not a fan, in a hot room. And get them out of the hot room if you possibly can.

What heat exhaustion looks like

The CDC lists these among the things that happen when the body gets too hot: muscle cramping, unusually heavy sweating, shortness of breath, dizziness, headache, weakness, and nausea.

Somebody in that state needs to stop, get cool, get out of the sun, and take fluids. And they need watching, because heat exhaustion is not a stable condition — it is a stage. It becomes heat stroke if the body loses the argument.

Which is the reason this page does not have a section telling you when it is fine to stay home. If somebody is sick from heat and you are watching them, you are watching something that can change. If you are unsure, come in — this list is not exhaustive and you are not expected to diagnose anybody.

Sweating stopping is not a good sign

Worth stating on its own, because it is the detail that misleads people most.

As heat illness progresses, sweating can stop. Skin that has gone hot and dry after a period of heavy sweating is not somebody cooling down and recovering — it can be the body’s cooling system failing. Combined with confusion it is the classic picture of heat stroke.

Do not read the absence of sweat as improvement.

Who gets into trouble fastest

Nobody is exempt, and heat is harder on some people than others: older adults, very young children, anyone working or exercising outdoors, and anyone with heart, lung or kidney disease.

And medication matters. A number of common medicines affect how the body handles heat and how it holds water. The CDC’s instruction is plain and worth repeating exactly: do not stop or change your medicines until you talk to your doctor. Adjusting a prescription because of a heat wave is a conversation, not a decision to make in July.

And the standing advice to drink more water is not universal. The CDC qualifies it in its own words: “If your doctor limits the amount of fluids you drink or has you on water pills, ask them how much you should drink during hot weather.” If that describes you, the number is your prescriber’s to give — and it is a better question in April than in July.

What to do about the heat you cannot escape

If the problem is that a home is not cool enough, Arizona publishes a heat relief locator at heat.az.gov — cooling centres and hydration stations, maintained by the state rather than by us, which is why it stays current when this page would not.

Questions people actually ask

They are cramping badly but thinking clearly. Emergency? Cool them, get fluids in, and watch them. Cramping is on the CDC’s list of what happens when the body gets too hot. If confusion appears, or they are not improving, that is a 911 call.

How fast can heat stroke happen? Faster than people expect, and faster in a car, in direct sun, or during exertion. This is not a condition that gives you a comfortable amount of warning.

Can I put them in a cold shower? Getting cool water onto skin is the goal. Do not put anybody who is confused or not fully alert into water where they could slip under — cold cloths and compresses are safer and nearly as effective.

Should I give them something to drink? Only if they are fully alert and able to swallow safely. Never try to give fluids to somebody who is confused or drowsy.

It is 105 outside and I feel awful. Is that heat exhaustion? Possibly. Stop, get cool, drink, and if it is not settling or you start feeling confused, come in.

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If somebody is confused, stumbling or unconscious in the heat, call 911 and start cooling them. For heat illness that is not improving, both of our emergency rooms are open 24 hours a day, every day of the year — walk in, with CT, X-ray and a full laboratory in the building. Find your nearest emergency room →

Related reading: which door do you need · what our emergency rooms can do

Sources

12. Heat emergencies — MedlinePlus Medical Encyclopedia, U.S. National Library of Medicine. https://medlineplus.gov/ency/article/000056.htm
13. About Heat and Your Health — Centers for Disease Control and Prevention. https://www.cdc.gov/heat-health/about/index.html
24. Heat and Older Adults (Aged 65+) — Centers for Disease Control and Prevention. https://www.cdc.gov/heat-health/risk-factors/heat-and-older-adults-aged-65.html

This article is general information, not a diagnosis, and it cannot account for anyone’s history or medications. It gives no doses. If you are unsure, come in — this list is not exhaustive and you are not expected to diagnose anybody. If it might be an emergency, treat it as one and call 911.