Heat stroke vs heat exhaustion: symptoms, differences and when to get help

What is the difference between heat exhaustion and heat stroke?

Heat exhaustion happens when the body loses too much water and salt, usually through heavy sweating. Heat stroke is the more dangerous stage, when the body can no longer control its temperature and it keeps climbing.

The clearest difference is how the person is thinking. Someone with heat exhaustion feels sick but still thinks clearly. Someone with heat stroke is confused, slurring words or passing out, and needs an ambulance.

Heat stroke vs heat exhaustion: key differences at a glance

Both are heat-related illnesses that start with heat stress. Heat exhaustion can turn into heat stroke if nothing is done, so knowing the signs of each helps you act before a rough afternoon turns into an emergency.

Most signs come from OSHA's heat illness guidance and CDC's heat-related illness chart.

Heat exhaustion vs heat stroke: how to tell them apart

Sweat alone doesn't settle it. OSHA lists both heavy sweating and hot, dry skin as signs of heat stroke, so don't rule it out because someone is still sweating.

How do you tell heat stroke from heat exhaustion?

You don't need a diagnosis to act. OSHA says diagnosis is often difficult because several heat illnesses can show up together, so its rule is simple: when in doubt, call 911. Three quick checks still point you in the right direction.

• Ask a simple question. Ask for their name, the date or where they are. Confusion or slurred speech means heat stroke.

• Check the skin and pulse. Cold, clammy skin and a fast, faint pulse point to heat exhaustion. Hot, red skin and a fast, strong pulse point to heat stroke.

• Take their temperature if you can. A reading above 41°C (106°F) points to heat stroke, but a lower reading doesn't rule it out, so don't wait for a thermometer before you act.

Cleveland Clinic names signs of brain dysfunction as the key difference. Heat stroke has them and heat exhaustion doesn't.

Picture a laborer on the second hot afternoon of a heat wave. He's pale, soaked in sweat and says he feels sick. That's likely heat exhaustion, so get him into shade and start cooling him. If he starts slurring his words or can't tell you where he is, treat it as heat stroke and call 911.

How do you give first aid for heat illness?

OSHA's first aid standards require employers to keep first aid personnel and equipment ready. The steps below follow guidance from OSHA, NIOSH and CDC. Stay with the person the whole time, because heat illness can get worse fast.

Heat exhaustion treatment: what to do

1. Move the person to a cool place, like shade or air conditioning.

2. Loosen or remove extra clothing, including shoes and socks.

3. Cool them with cold wet cloths, or have them wash their head, face and neck with cold water.

4. Give frequent sips of cool water.

5. Stay with them until they feel better.

Get medical help right away if the person is vomiting, gets worse or doesn't feel better within an hour, says CDC. For workers, NIOSH advises a medical evaluation, and a 911 call if care isn't available.

Heat stroke treatment: what to do

1. Call 911 right away.

2. Stay with the person until help arrives.

3. Move them to shade or a cool room and remove outer clothing.

4. Cool them fast. An ice bath or cold water immersion is, per OSHA, the best way to cool workers rapidly in an emergency. If you can't, wet their skin and put cold wet cloths or ice on the head, neck, armpits and groin.

5. Fan them to speed up cooling.

6. Don't give them anything to drink, CDC advises.

Where do heat cramps and heat syncope fit in?

Heat cramps and heat syncope are all part of heat-related illnesses. They are milder, but they can be early warnings. Heat cramps are painful muscle spasms in the legs, arms or stomach after heavy sweating, and they can also be a symptom of heat exhaustion. Heat syncope is a short fainting spell or dizziness, often after standing too long or getting up suddenly.

How should supervisors prepare for a heat emergency?

Don't wait for the first case to work out a plan. NIOSH says workers and supervisors should be trained on heat-related illnesses, their symptoms and first aid. Before a hot spell:

• Keep cooling supplies where the crew works. OSHA says to make an ice bath by putting all the available ice into a large container of water.

• Set up a shaded or air-conditioned spot to cool people down.

• Name who calls 911 and who stays with the person.

• Post the site address and gate directions where everyone can see them.

• Brief new workers on the warning signs during their first few days.

A heat action plan helps you write all of this down in one place.

How can you lower the risk of heat illness at work?

This guide covers spotting and treating each illness. For full heat stress prevention steps, read our guide to heat illness prevention. The short version is OSHA's formula of water, rest and shade.

New workers are at higher risk, so OSHA says all symptoms should be taken seriously in the first few days on the job. Employers can see what's expected of them in our guide to OSHA heat regulations, and our heat stress guide explains how heat builds up on site.

You can also brief your crew with a heat stress toolbox talk before the next hot spell.