Heat Stroke Symptoms: Full List and Warning Signs
Heat stroke does not usually announce itself with one dramatic sign. It builds, often quietly, through warning signs that look like heat exhaustion until they don't. By the time a bystander is sure something is wrong, the window for easy recovery has narrowed.
This article is a working reference. If you suspect heat stroke right now, call emergency services and start cooling the person immediately — read the rest later.
The cardinal symptoms
These are the signs that define heat stroke. Any one of them in a hot person is enough to treat the situation as heat stroke until proven otherwise:
- Core temperature above 40°C (104°F) if a thermometer is available
- Altered mental status — confusion, irritability, agitation, slurred speech, irrational behavior, hallucinations
- Seizure or loss of consciousness
- Hot skin — dry in classic heat stroke, drenched in exertional
If a hot person stops making sense, the diagnosis is heat stroke. Everything else on this page is secondary.
Early warning signs
Most heat stroke is preceded by a window of milder symptoms. People who collapse from heat have almost always been telling you, in retrospect, that they were in trouble:
- a persistent throbbing headache that does not respond to water and shade
- nausea or queasiness
- light-headedness or dizziness on standing
- muscle cramps in calves, thighs, abdomen
- unusual fatigue or weakness
- profuse sweating that suddenly slows or stops
- skin that flushes deep red, or turns pale and waxy
- racing heart rate at rest
- breathing that is faster and shallower than usual
- urine that has turned dark amber or stopped altogether
Catching this window is what separates a manageable heat illness from a medical emergency. If two or three of these are present together in a hot environment, stop the activity, get to shade, cool the body, and drink slowly.
Neurological symptoms — the most important category
The brain is one of the first organs to suffer in heat stroke, and neurological signs are the strongest predictor of severity:
- Confusion about time, place, or task — the person cannot remember where they are or what they were doing
- Irritability that seems out of character — snapping at people, sudden anger
- Slurred speech or trouble finding words
- Difficulty walking — stumbling, swaying, an unsteady gait
- Irrational behavior — undressing in cold, refusing help, insisting on continuing exertion
- Hallucinations — seeing or hearing things that are not there
- Seizures — generalized or focal
- Loss of consciousness — brief faint or sustained coma
Any of these in a hot person is a medical emergency. Do not wait for "more" symptoms — the brain change is the symptom.
Cardiovascular symptoms
The heart works much harder in heat as it pumps blood to the skin for cooling, and signs of cardiovascular strain commonly appear:
- rapid heart rate, often 130 to 180 beats per minute at rest
- a pounding pulse early in the course
- a weak, thready pulse late in the course as the heart begins to fail
- low blood pressure or fainting on standing
- chest pain or tightness
- cool, mottled extremities despite hot core
Skin and sweating
The classic teaching of "hot dry skin equals heat stroke, sweaty skin equals heat exhaustion" is only half right. Exertional heat stroke usually presents with profuse sweating because the person was working hard until they collapsed. Classic heat stroke in elderly people during heat waves more often shows hot dry skin because the cooling system has been overwhelmed for days.
What to look for either way:
- skin much hotter than expected to the touch
- a deep flushed red, especially face and chest
- in late stages, pale or waxy skin as circulation fails
- absent sweating in someone you would expect to be sweating
- goosebumps in a hot environment — an ominous sign of impending collapse
Gastrointestinal symptoms
The gut does not get much blood when the body is shunting circulation to the skin and brain. Common signs:
- nausea
- vomiting, sometimes repeated
- diarrhea
- abdominal cramping
- a sudden, profound loss of appetite
- a metallic or strange taste in the mouth
Vomiting in a confused or unconscious person is a major airway risk and one of the reasons heat stroke calls for emergency services rather than self-management.
Respiratory symptoms
Breathing patterns change as the body tries to dump heat:
- rapid, shallow breaths
- a sense of air hunger
- a dry burning sensation in the throat
- in severe cases, irregular breathing or apnea
Late and end-stage signs
These are the signs that mean the situation has progressed beyond a backyard or trailhead response, and the patient needs hospital care immediately:
- core temperature above 41°C
- coma or unresponsiveness
- new seizures
- breathing failure
- visible bleeding from gums, nose, or under the skin (a sign of clotting failure)
- a drop in urine output to nothing
- cardiac arrest
If you reach this part of the symptom list and you are not already on the phone with emergency services, that is the priority right now.
Symptoms that vary by population
Symptoms do not look identical across groups:
- Elderly people during heat waves often skip the dramatic early-warning phase entirely. A confused, withdrawn, sleepy older person in a hot apartment may be in classic heat stroke without ever having complained.
- Infants and small children show fussiness, refusal to drink, a hot dry diaper, sunken fontanelle, and lethargy more than they show "classic" complaints.
- Athletes often present with a sudden collapse mid-event after appearing fine moments earlier. Exertional heat stroke can crash a fit young person from "feeling pretty bad but pushing through" to unconscious in minutes.
- People on certain medications (diuretics, antihypertensives, anticholinergics, antipsychotics, stimulants) can have blunted thirst, blunted sweating, or both, and lose the normal early warning signs.
What to do when symptoms appear
Two paths, depending on severity:
If only early warning signs are present — stop the activity, move to shade or air conditioning, drink cool water steadily, apply cool wet cloths, and rest for at least an hour. If the person is not noticeably better in 30 minutes, escalate.
If any cardinal sign is present — call emergency services and start aggressive cooling immediately. Cold-water immersion is the gold standard. If that is not possible, douse with cold water and use the strongest air movement available, and pack ice at neck, armpits, and groin. Do not stop cooling until help arrives.
Do not give fever-reducing medications. Heat stroke is not a fever, and acetaminophen or ibuprofen will not lower the core temperature.
Where Pressure Pal fits in
Pressure Pal is built around the barometric pressure forecast and is most directly useful for migraine and weather-sensitivity tracking. On dangerous heat days, pair it with a standard weather app's heat index and humidity views, and you have a useful at-a-glance picture for planning around the worst hours of the day — particularly if you are in a high-risk group or care for someone who is.
The same daily forecasting habit that helps weather-sensitive people protect their migraine threshold also helps them spot dangerous heat stretches before they arrive.
Bottom line
Heat stroke symptoms cluster around four signals: very high core temperature, altered mental status, hot skin, and a fast or failing pulse. A throbbing headache, nausea, dizziness, and unusual fatigue are the warning shots in front of that. Treat the warning shots as warning shots and the cardinal signs as a medical emergency.
If a hot person stops making sense, that is heat stroke until proven otherwise.