Heat Exhaustion vs Heat Stroke
Short answer
Heat exhaustion vs heat stroke comes down to the brain: heavy sweating, weakness and nausea mean exhaustion, while confusion, collapse or a body temperature above 103°F mean heat stroke and a call to 911.
Swelter Almanac, checked against the sources · updated
Points on this page
The forecast in brief
- Ready.gov lists a body temperature above 103°F as a sign of heat stroke and says to call 9-1-1 or get the person to a hospital right away.
- Once heat stroke starts, body temperature can climb to 106°F or more within 10 to 15 minutes (CDC/NIOSH).
- Heat exhaustion that worsens or lasts longer than an hour needs a call to a health care provider (Ready.gov).
- Skin is not a reliable test: NIOSH lists "hot, dry skin or profuse sweating" for heat stroke.
- Cramps that do not ease within 1 hour call for medical help, and NIOSH advises against salt tablets.
- At 90°F and 70% humidity, the NWS heat index equation gives about 106°F, inside the Danger band.
Heat illness runs along a line, with cramps and heavy sweating at the mild end and heat stroke at the dangerous one. This page sets out the signs as the CDC's occupational safety institute (NIOSH) and Ready.gov publish them, the first aid that buys time, and the point where you stop watching and call for help.
What is the difference between heat exhaustion and heat stroke?
Heat exhaustion is the body straining to shed heat; heat stroke is that system failing, and it can kill. With exhaustion, sweating usually keeps going and the person stays alert, if miserable. With heat stroke, the brain is affected: NIOSH lists confusion, altered mental status, slurred speech, seizures and loss of consciousness, and warns that it is fatal if treatment is delayed.
The practical test is behavior. Someone who is tired, dizzy and sweating but can answer questions clearly likely has heat exhaustion and needs to cool down now. Someone who is confused, acting oddly, or cannot stay awake needs 911, whatever their skin looks like.
| Condition | Common signs | First move | When to get help |
|---|---|---|---|
| Heat cramps | Muscle pain or spasms in the stomach, arms or legs | Water plus a snack or sports drink | Cramps past 1 hour, heart problems or a low-sodium diet |
| Heat exhaustion | Heavy sweating, weakness, dizziness, headache, nausea, thirst | Cooler place, loosen clothing, sip water | Worse, or lasting over an hour: call a provider |
| Heat stroke | Confusion, slurred speech, seizures, collapse, temperature above 103°F | Call 911, then cool the person | Always, right away |
What are the signs of heat exhaustion?
The signs of heat exhaustion are heavy sweating, weakness, dizziness, headache and nausea, often with thirst. Ready.gov's list adds paleness, muscle cramps, tiredness, a fast or weak pulse, fainting and vomiting. NIOSH's worker list adds irritability, an elevated body temperature and decreased urine output, which is worth watching in anyone who has been in a hot house all day.
Older adults may not notice thirst until they are already behind on fluids. The older adults page covers why, and how medicines such as diuretics change the picture.
What are the signs of heat stroke?
The signs of heat stroke are a very high body temperature with a change in the brain: confusion, slurred speech, fainting or unconsciousness, or seizures. Ready.gov describes red, hot, dry skin with no sweating, a rapid and strong pulse, and dizziness. NIOSH, however, notes the skin can be hot and dry or soaked with sweat, so sweating does not rule heat stroke out.
Speed matters. According to CDC/NIOSH, the body can reach 106°F or higher within 10 to 15 minutes once heat stroke begins.
The thresholds that matter
- 103°F+Body temperature listed as a heat stroke signReady.gov
- 106°FTemperature heat stroke can reach in 10 to 15 minutesCDC/NIOSH
- 1 hourExhaustion or cramp symptoms lasting longer need medical helpReady.gov; CDC/NIOSH
- 15°FExtra heat index that full sun can addNWS
What first aid helps while you wait?
For heat stroke, call 911 first, then cool the person as fast as you can and stay with them until help arrives. NIOSH's steps: move them to a cool, shaded area, take off outer clothing, and cool them quickly, using a cold-water or ice bath if one is possible. Otherwise wet the skin, put cold wet cloths or ice on the head, neck, armpits and groin, soak their clothes with cool water, and fan the air around them. Don't try to make a confused or unconscious person drink anything; they could choke.
For heat exhaustion, get the person out of the heat, remove extra clothing (shoes and socks too, NIOSH says), and, if they are fully alert, give frequent sips of cool water or a sports drink. Cold compresses or washing the head, face and neck with cold water help. Have someone stay with them, and if the person becomes confused or drowsy, treat it as heat stroke and call 911.
If the house itself is the problem because the A/C quit, the A/C breakdown page covers keeping people safe while a repair is arranged.
When should you call 911?
Call 911 for any sign of heat stroke: confusion, slurred speech, fainting, a seizure, unconsciousness, or a temperature above 103°F. Ready.gov's instruction is to call 9-1-1 or take the person to a hospital immediately. Don't wait to see if cooling works first; start cooling while help is on the way.
Heat exhaustion usually starts with self-care, but it becomes a 911 call when the person faints, becomes confused, keeps vomiting, or when no clinic or doctor can be reached; NIOSH says to call 911 if medical care is unavailable. For milder cases that get worse or last more than an hour, call a health care provider. Heat cramps need medical help when they last more than an hour or the person has heart trouble or follows a low-sodium diet.
How does the heat index change the risk of heat stroke?
The higher the heat index, the faster the body runs out of ways to cool itself, and the NWS ties each band to the illnesses it makes likely. On the NWS Amarillo table, Extreme Caution (90°F to 103°F) makes heat stroke, cramps or exhaustion possible with prolonged exposure; Danger (103°F to 124°F) makes cramps or exhaustion likely and heat stroke possible with prolonged exposure; Extreme Danger (125°F and up) makes heat stroke highly likely.
Humidity does much of the damage. The NWS equation turns 85°F air at 70% humidity into a heat index near 93°F, and 95°F at 60% into about 113°F. Those numbers assume shade; full sun can add up to 15°F. Gulf Coast readers will find more on damp indoor air in the humid heat section, and the heat safety hub has the full band table.
How this page was put together
Signs and first aid follow two primary sources only: the CDC/NIOSH heat-related illnesses page (dated March 3, 2026) and Ready.gov's extreme heat page, both read in October 2026, with heat index bands and equation from the National Weather Service. Where they differ on heat exhaustion, this page follows Ready.gov for home care and NIOSH for the 911 trigger when care is unavailable. Home remedies, forum advice and anything not on those pages were left out. This page is general information, not medical advice.
More questions
Should someone with heat exhaustion be left alone to rest?
No. NIOSH says to have someone stay with the person until help arrives. Watching them is how you catch the change to confusion or fainting that turns a rest-and-cool situation into a 911 call.
Should you give salt tablets for heat cramps?
No. CDC/NIOSH specifically says to avoid salt tablets. Water plus a snack or a sports drink that replaces carbohydrates and electrolytes is the listed first step.
Is an ice bath safe for heat stroke?
NIOSH lists a cold water or ice bath as one way to cool a person quickly, if one is possible. Cold wet cloths or ice on the head, neck, armpits and groin also work while you wait for emergency help.
Does someone with heat stroke always stop sweating?
No. Ready.gov describes dry skin with no sweating, but NIOSH lists hot, dry skin or profuse sweating. Confusion and a very high temperature matter more than whether the skin is wet.
What is heat rash, and is it dangerous?
NIOSH describes heat rash as red clusters of small pimples or blisters, often on the neck, upper chest and skin folds. Keeping the area dry and moving to a cooler, less humid space help; NIOSH says to skip ointments and creams.
What does dark urine mean in the heat?
Decreased urine output is on NIOSH's list of heat exhaustion signs, and tea- or cola-colored urine after heavy exertion is a warning sign of rhabdomyolysis, which needs immediate medical care. Either one is a reason to stop, drink and get checked.