What Are the Symptoms of Heat Stroke?

Heat stroke is a medical emergency in which the body has lost the ability to keep its core temperature in a safe range. Once that line is crossed, the symptom picture changes — and the change is the diagnosis. Understanding the symptoms of heat stroke is not just about memorizing a list. It is about recognizing the shifts that separate heat stroke from heat exhaustion, the cluster of signs that get a person rushed to a hospital.

This article walks through the symptoms, system by system, with notes on what causes each one and when the picture is severe enough to warrant calling emergency services.

The defining symptom: change in mental status

If there is one symptom of heat stroke that matters more than the rest, it is a change in mental status. People with heat exhaustion are uncomfortable, but they know who they are, where they are, and what is happening. People with heat stroke have lost some part of that orientation.

The change can look like:

• Confused or rambling speech
• Slurred or thick speech
• Disorientation about time, place, or people
• Agitation or unusual aggression
• Quiet withdrawal — the person stops responding the way they would
• Bizarre behavior in someone who is normally composed
• Drowsiness that does not lift with stimulation
• Loss of consciousness
• Seizure

A coherent person with heavy sweating, headache, and weakness is in heat exhaustion territory. A confused, slurring, agitated, or unresponsive person with the same physical signs is in heat stroke until proven otherwise. That distinction drives the entire emergency response.

Core temperature symptoms

The body's normal core temperature sits around 98.6°F (37°C). Heat stroke is diagnosed at a core temperature above 104°F (40°C) with neurological symptoms.

Without a thermometer, the symptoms that suggest the core has crossed that line are:

• Skin that feels hot to the back of someone else's hand — much hotter than the surrounding air can explain
• A sense that the person is "burning up" inside
• A flush that has gone past pink to deep red or purple
• A complete failure to respond to cooling for several minutes
• Confusion or other neurological change

A rectal or ear thermometer reading confirms the diagnosis, but in the field the symptom cluster plus neurological change is enough to start treating as heat stroke.

Skin and sweating symptoms

Heat stroke has two common skin presentations, depending on how it developed.

Classic (non-exertional) heat stroke develops over hours or days, usually in older adults in a heat wave, often without much physical exertion. The hallmark symptom is hot, dry, flushed skin. The body has run out of sweat or the sweat response has failed. The skin feels hot and almost papery.

Exertional heat stroke develops in hours or even minutes, usually in someone who has been working or training hard in heat. The skin can still be soaked with sweat even though the body is overheating. The flush is deep and uniform. The sweating is the body's last attempt to cool down, and it is no longer keeping up with the heat load.

A symptom shift that is especially telling: sweating suddenly stops in someone who had been drenched a moment before. That is the sweat response failing, and it is a marker that heat stroke has begun.

Cardiovascular symptoms

The heart and circulation are under massive strain in heat stroke:

• A very fast pulse — often above 130 bpm at rest, sometimes well above
• A bounding, strong pulse rather than the weak pulse of heat exhaustion (though weak pulses also occur)
• Low blood pressure in severe cases
• Chest tightness or pressure
• Shortness of breath at rest
• Skin and lips that have gone bluish in the most severe cases (a late symptom)

In someone with cardiovascular disease, the symptoms can resemble a cardiac event, and the two can occur together — heat stress can precipitate one.

Neurological symptoms beyond mental status

Heat stroke is fundamentally a brain injury caused by overheating, so neurological symptoms extend beyond simple confusion:

• Severe, often throbbing headache
• Dizziness or vertigo
• Visual changes — blurred vision, tunnel vision, spots
• Hearing changes — muffled hearing or ringing
• Loss of coordination, staggering, falling
• Slurred speech
• Inability to walk a straight line
• Seizures, focal or generalized
• Coma

Headache severity is striking. A person with heat stroke often describes the worst headache of their life, with pressure behind the eyes and across the temples. For weather-sensitive people who are familiar with migraine, the heat stroke headache is qualitatively worse.

Gastrointestinal symptoms

The GI symptoms in heat stroke can be severe:

• Nausea, often violent
• Vomiting, sometimes repeated
• Diarrhea
• Severe abdominal cramping

Vomiting in heat stroke is especially dangerous because it prevents the person from being able to keep down fluids and accelerates dehydration just as the body needs water most. Repeated vomiting on a hot day is one of the clearest reasons to call for emergency help rather than try to handle it at home.

Respiratory symptoms

Breathing becomes part of the cooling effort and the strain shows:

• Rapid, shallow breathing
• Panting
• A sense of not getting enough air
• Sometimes a hyperventilation pattern that adds tingling in the fingers and around the mouth

In severe cases, breathing slows or becomes irregular as the brain function deteriorates.

Muscular symptoms

Muscles do not escape the symptom picture:

• Severe cramping in the calves, thighs, abdomen, and back
• A sense of weakness that prevents the person from standing
• Twitching or fasciculations
• In the most severe cases, muscle breakdown that produces tea-colored urine and damages the kidneys (rhabdomyolysis)

Muscle breakdown is one of the reasons heat stroke is dangerous even after the temperature has come down — the released muscle proteins can injure the kidneys days later.

Symptoms that signal "call 911 now"

Any of these symptoms in someone who has been hot for hours is a call-for-help moment:

• Confusion, slurred speech, or odd behavior
• Loss of consciousness, even briefly
• Seizure
• Skin that feels extremely hot — visibly red, flushed, or very pale
• Vomiting that prevents fluid intake
• Severe shortness of breath
• Chest pain
• A core temperature reading above 103°F (39.4°C) with any of the above

Do not wait to see if the person recovers. Heat stroke worsens quickly and the window for safe field cooling is short.

How the symptoms shift over time

Heat stroke is a moving target. Early in the episode the symptoms can resemble a bad case of heat exhaustion — headache, nausea, fast pulse, weakness, light-headedness. The shift into heat stroke shows in:

• Mental status change first
• Sweating reduction or sudden cessation
• A skin shift to very hot rather than clammy
• Pulse that becomes very fast or irregular
• Confusion that deepens rather than lifts with rest and water

Catching that shift is the difference between a hot day with a hard recovery and a hospital stay.

What about exertional heat stroke in trained athletes?

The symptom picture in exertional heat stroke can be misleading. A trained athlete may still be sweating heavily, may not look obviously red, and may push through what they think is a bad day. The classic warning signs in this group are:

• A pace that drops without explanation
• Confusion or unusual irritability on the course
• A collapse near the finish line
• Stumbling, weaving, or falling
• Slurred speech in conversation
• A teammate or coach saying "something is off"

Coaches, race officials, and training partners are often the first to recognize exertional heat stroke. Trust the outside view.

Bottom line

The symptoms of heat stroke fall across every system — skin, circulation, brain, gut, lungs, muscles — but the diagnostic core is straightforward: a body that is too hot and a brain that is no longer working normally. Hot skin, confusion, slurred speech, vomiting, severe headache, fast pulse, collapse — any of those in the heat is heat stroke until proven otherwise. The response is to cool aggressively and call for emergency help in parallel.

If you are also weather-sensitive and prone to headaches in summer pressure patterns, Pressure Pal can help you watch the trends that often line up with the hottest days, so you go into peak heat aware and prepared.