Heat Stroke vs Heat Exhaustion: How to Tell and How to Cool
The one finding that separates heat stroke from heat exhaustion, why sweating and a normal oral temperature do not rule it out, classic and exertional heat stroke, and why rapid cooling comes first.
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Heat exhaustion and heat stroke sit on the same spectrum, and the line between them is the brain. A patient with heat exhaustion is hot, tired, sweaty and sick but thinking clearly. A patient with heat stroke has a body temperature high enough to injure organs, and the first organ to show it is the brain: confusion, odd behavior, collapse or seizures. Heat stroke is a true emergency, and how fast the patient is cooled decides how they do.
The one question that separates them
Is the patient's mental status normal? A hot patient who is confused, combative, disoriented, unusually drowsy, staggering, seizing or unresponsive should be treated as heat stroke until proven otherwise. Do not wait for a temperature reading, for dry skin or for a high number to make the call.
Dry skin is the classic textbook sign, and it misleads. Many patients with exertional heat stroke, such as runners, athletes, soldiers and workers, are still sweating when they collapse. Dry, hot skin is more typical of classic heat stroke in an older or chronically ill person who has been in a hot environment for days.
Heat exhaustion and heat stroke side by side
| Feature | Heat exhaustion | Heat stroke |
|---|---|---|
| Mental status | Normal. The patient may feel weak, dizzy or irritable but is oriented | Altered: confusion, combativeness, collapse, seizures or coma |
| Body temperature | Raised, typically below 40 °C (104 °F) | Generally above 40 °C (104 °F), measured as core temperature |
| Skin | Usually sweaty and may be pale or flushed | Sweaty in many exertional cases; often hot and dry in classic cases |
| Other findings | Headache, nausea, fatigue, fast heart rate, fainting on standing | Fast heart rate, fast breathing, low blood pressure, vomiting, possible bleeding problems and organ failure later |
| Course | Improves with rest, cooling and fluids | Worsens without rapid cooling; can be fatal |
The temperature figures above follow the 2023 expert consensus statement on exertional heat illness from ACSM, the national sports medicine college; the earlier NATA (athletic trainers) position statement uses about 40.5 °C (105 °F). They are a guide, not a cutoff: a patient with altered mental status and a temperature a little under 40 °C is still managed as heat stroke.
Classic and exertional heat stroke
| Feature | Classic heat stroke | Exertional heat stroke |
|---|---|---|
| Who | Older adults, young children, people with chronic illness or on medications that impair heat loss, people without cooling at home | Healthy, active people: athletes, runners, military recruits, outdoor workers |
| How it develops | Over hours to days of hot weather, often during a heat wave | Over minutes to hours of hard exertion, sometimes on a day that does not feel very hot |
| Skin | Often hot and dry | Often still sweating |
| Cooling | Rapid cooling still matters; immersion may be impractical for a frail patient | Cold water immersion is the most effective method |
Cooling: the treatment is time
For exertional heat stroke the ACSM consensus is direct: cool first, transport second. The damage done by heat stroke depends on how high the temperature goes and for how long, and whole-body immersion in cold or ice water cools faster than anything an ambulance can do on the move. Where an event medical team or an athletic trainer has an immersion tub ready, cooling on scene before transport is what the consensus recommends, and the consensus advises cooling until the core temperature reaches about 39 °C (102 °F), then removing the patient from the water so they do not overshoot.
Most EMS crews do not carry an immersion tub. Whether to cool on scene or cool during transport is a protocol decision, and some systems now carry equipment for it, such as a body bag or tarp filled with ice water. Without immersion, use the most aggressive cooling you have:
- Move the patient out of the heat and remove excess clothing and equipment.
- Cover the body with cold, wet towels or ice-water towels and rotate them often as they warm.
- Combine water on the skin with moving air: misting and fanning, or the vehicle's air conditioning on high.
- Ice packs to the neck, armpits and groin help but are slow on their own. Use them as an addition, not as the plan.
- Tell the receiving facility early that you have a heat stroke patient so cooling continues without a gap.
Support the airway, breathing and circulation as the patient needs, check a blood glucose level in any patient with altered mental status, and watch for seizures and vomiting. Fluids and any medication are given as your protocol directs.
Heat exhaustion: rest, cool and reassess
Move the patient to a cool place, lay them down, loosen or remove clothing, cool the skin and give fluids as your protocol allows. Reassess the mental status repeatedly. A patient who becomes confused, or whose temperature keeps climbing despite cooling, has moved toward heat stroke and should be treated that way.
The milder heat illnesses
- Heat cramps: painful muscle spasms during or after hard work in the heat, with a normal mental status and normal or near-normal temperature. Rest, cooling, stretching and fluid and salt replacement usually settle them.
- Heat syncope: fainting or near-fainting, usually on standing still or standing up after exertion in the heat, as blood pools in the legs and skin. Lay the patient flat, cool them and reassess. A patient who does not recover quickly, or who has altered mental status after the faint, needs a fuller workup, because fainting has many causes besides heat.
The short version
- The difference between heat exhaustion and heat stroke is the brain. Altered mental status in a hot patient means heat stroke until proven otherwise.
- Sweating does not rule out heat stroke, especially in an athlete or worker who collapsed while exerting.
- A normal temperature by mouth, ear, forehead or armpit does not rule it out either.
- Cooling is the treatment and time matters. Cold water immersion is the most effective method for exertional heat stroke.
- Whether you cool before or during transport is your protocol's decision. Whatever you have, cool aggressively and tell the hospital early.