Heat stroke vs heat exhaustion: signs and first aid

In short

• Heat stroke is a medical emergency. Signs include confusion, a very high temperature, hot skin and sometimes a seizure or loss of consciousness.
• Heat exhaustion comes with heavy sweating, pale clammy skin, weakness, dizziness, headache and nausea. Untreated, it can progress to heat stroke.
• Call 911 for heat stroke and start cooling the person right away. Do not drive them yourself.
• For heat exhaustion, move the person somewhere cool, remove extra clothing, cool the skin and give water.
• Older adults, young children, outdoor workers and people with chronic conditions or certain medicines are at higher risk.

What happens in the heat

Normally the body cools itself by sweating. In hot, humid weather, or during strenuous exercise or work, sweating may not be enough, and body temperature can reach dangerous levels. Most cases happen after staying in the heat too long.

Heat illness covers a range: heat rash (skin irritation from heavy sweating, more common in young children), heat cramps (muscle pains or spasms during heavy exercise), heat exhaustion and heat stroke. The WHO calls heat stroke a medical emergency with a high fatality rate.

The WHO adds that health effects of heat often appear on the same day or within a few days, and that heat can worsen heart, lung, kidney, mental health and diabetes conditions.

Heat exhaustion or heat stroke?

Heat exhaustion can develop after several days of high temperatures with not enough fluids. Heat stroke can come on within minutes.

• Heat exhaustion: heavy sweating with pale, clammy skin, tiredness, dizziness, headache, nausea or vomiting, muscle cramps, intense thirst, rapid breathing and a fast, weak pulse.
• Heat stroke: a very high temperature, hot skin with little or no sweating, a rapid, strong pulse, fast breathing, dizziness, nausea, confusion or restlessness, seizures or loss of consciousness.
• The deciding sign is a change in thinking or behavior. Someone in the heat who is confused, restless or passes out should be treated as having heat stroke.

Because the signs overlap, treat any doubtful case as the emergency and cool the person while you wait for help.

What to do for heat exhaustion

1. Get out of the heatMove the person to a cool place, in shade or air conditioning, and have them lie down.
2. Loosen clothingRemove extra clothing.
3. Cool the skinUse cool water, fanning, or cold packs under the armpits or on the neck.
4. Give fluidsIf the person is awake and alert, offer water or an oral rehydration drink in small sips.
5. Stay with themThey should start to feel better within about 30 minutes. If they do not, or they get worse, call 911.

What to do for heat stroke

1. Call 911 at onceDo not drive the person to the hospital yourself.
2. Cool them while you waitMove them out of the heat and cool them with a wet sheet, fanning or cold sponging, and cold packs on the neck and armpits.
3. Also call if they stay unwellCall 911 as well if someone is still unwell after 30 minutes of cooling and rest.
4. If they pass outPlace them in the recovery position, check their breathing and pulse, and start CPR if there are no signs of life.

Who is at higher risk, and prevention

Anyone can be affected, but risk is higher for adults 65 and older, infants and young children, pregnant people, people with heart disease, asthma or other chronic conditions, people who live alone, outdoor workers, athletes, people who drink alcohol and people taking certain medicines. Some medicines can cause dehydration or overheating. Do not stop or change a medicine without talking to your doctor, but do ask whether it matters in hot weather.

• Drink fluids throughout the day. Light yellow or clear urine usually means you are drinking enough. Limit sugary, high-sodium, caffeinated and alcoholic drinks.
• Wear light, loose clothing and avoid the sun in the middle of the day.
• Plan outdoor activity for the coolest part of the day, take breaks in shade and limit strenuous activity.
• Use air conditioning or find a cooling center. Fans help only up to around 90 degrees Fahrenheit, since above that they can raise body temperature.
• Check on older relatives, neighbors who live alone and pets.
• Never leave children or animals in a parked vehicle.

When to see a doctor, and red flags

Call 911 if someone in the heat is confused or acting strangely, has a seizure, loses consciousness, has hot dry skin, or is still unwell after 30 minutes of cooling and rest. A young child or an older adult who is not responding normally in a hot room or vehicle is also an emergency.

See your primary care provider if you have had heat illness before, if you take medicines or have conditions that raise your risk and want a plan for hot weather, or if symptoms such as cramps and weakness keep coming back.

What hospital care involves

Heat stroke is a medical emergency treated in hospital, and the sources used here do not describe the details, so leave that to the emergency team. Heat exhaustion that settles with cooling and fluids may need no further treatment, but ask a provider if you are unsure or if it keeps happening.

Questions and answers

Sources

1. CDC — Heat Stress and Heat-Related Illnesses
2. NHS — Heat exhaustion and heatstroke
3. MedlinePlus — Heat Illness
4. WHO — Heat and health

Sources checked on 29 October 2026.