Heat Stroke Symptoms and Warning Signs

Heat stroke is a medical emergency — call 911 immediately. It kills more Americans in an average year than hurricanes, tornadoes, and floods combined. But it also almost never happens without warning: heat exhaustion comes first, and knowing the difference is what lets you get help before it's dangerous.

This page summarises the CDC guidance on heat-related illness. It is not a substitute for medical care. If you have any doubt, call 911 or your local emergency number.

Heat exhaustion — the warning

Heat exhaustion happens when the body loses too much water and salt through sweating. It's serious but usually not immediately life-threatening if treated. Signs:

• Heavy sweating
• Cool, pale, clammy skin
• Headache, dizziness
• Nausea or vomiting
• Muscle cramps
• Weakness or fatigue
• Fast, weak pulse

What to do: Move to a cooler place. Loosen tight clothing. Sip cool water. Apply cool damp cloths to skin. Take a cool shower or bath. If symptoms don't improve within an hour, or if the person is vomiting or the symptoms worsen, get medical help.

Heat stroke — the emergency

Heat stroke is a 911 emergency. The body's cooling system has failed and core temperature is climbing dangerously high. Untreated, it causes brain, heart, and kidney damage — and can be fatal in minutes.

• Body temperature 103°F (39.4°C) or higher
• Hot, red, dry OR damp skin — sweating may have stopped, or skin may still be damp from earlier sweating
• Fast, strong pulse
• Headache
• Dizziness, confusion, slurred speech — altered mental status is the key sign
• Nausea
• Losing consciousness (fainting)

What to do — call 911 first. While waiting:

• Move the person to a cooler place.
• Reduce their body temperature with cool cloths or ice packs on the neck, armpits, and groin, or a cool bath.
• Do NOT give fluids to someone who is unconscious or barely responsive.
• Stay with them until emergency services arrive.

Other heat illnesses to watch for

Heat cramps — heavy sweating during exercise combined with painful muscle cramps or spasms, usually in the legs or abdomen. Stop activity, move to a cool place, drink water or a sports drink. Get medical help if cramps last more than an hour, if you're on a low-sodium diet, or if you have heart problems.

Sunburn — painful red skin that is warm to touch, small blisters may form. Stay out of the sun until it heals. Cool compresses, moisturiser, and NSAIDs help. See a doctor if the skin blisters over a large area, if you have fever or chills, or if a very young child is severely burned.

Heat rash — small red bumps or clusters of tiny blisters, usually on the neck, chest, groin, or in elbow creases. Keep the skin cool and dry. Powder can help.

Highest-risk groups

The CDC lists these groups as the most vulnerable to serious heat illness:

• Infants and children under 4
• Adults 65 and older — see our page on protecting kids, pets, and seniors.
• People with chronic conditions — heart disease, high blood pressure, diabetes, obesity, mental illness.
• Outdoor workers — construction, farming, delivery, roofing, landscaping.
• Athletes — especially during summer training.
• People taking certain medications — diuretics, some antipsychotics, some blood-pressure drugs, some allergy medications. Ask your pharmacist.
• People without home air conditioning — the single biggest risk factor in urban heat deaths.

Prevention

• Drink water regularly — a cup an hour during heat waves, don't wait to feel thirsty.
• Never leave anyone in a parked car. Interior temperatures can reach 125°F in minutes even on a mild day.
• Check on elderly neighbours and family at least twice a day during heat waves.
• Avoid outdoor exertion during the hottest hours (roughly 10am–4pm).
• Have a cooling plan. Public libraries and cooling centers are free and air-conditioned.
• Learn to stay cool without AC if your home doesn't have it — humid vs dry heat matters.

For an active cooling center, call 2-1-1 — free, 24/7, covering about 99% of US communities.