How do you stay safe in a heatwave?

Short answer. In a heatwave, stay out of the sun during the hottest hours, close windows and shutters by day ¹⁷⁸ and open them at night when the outside air is cooler ¹⁷. Drink water regularly, wet your skin and check on older people, babies and anyone living alone ¹⁷⁸. Heatstroke is a medical emergency: the CDC says body temperature can reach 106°F (41°C) or higher within 10 to 15 minutes ³.

Why is a heatwave dangerous, and how many people does it kill?

Heat stresses the body over several days and nights. The WHO notes that long periods of high day and night temperatures create cumulative stress on the body and raise the risk of illness and death ¹. It estimates about 489,000 heat-related deaths each year worldwide (2000–2019), 36% of them in Europe ¹. In Europe alone, an estimated 61,672 heat-related excess deaths occurred in the summer of 2022 ¹.

WHO/Europe calls heat stress the leading cause of climate-related death in its Region ². In 35 countries of the Region, heat claimed more than 60,000 lives in 2022 and 47,500 in 2023. Without further adaptation, that could rise to 120,000 heat-related deaths a year by 2050 ². In the United States, Ready.gov says extreme heat causes more deaths each year than any other weather hazard ⁴.

Who is most at risk?

The agencies list largely the same groups:

• Older people. The NHS names people aged 65 and over ⁷. The WHO and Santé publique France make the same point ¹⁸.
• Babies and young children. The NHS names children aged 5 and under ⁷. The WHO and WHO/Europe also list infants ¹².
• People with long-term conditions. These include heart, lung and kidney disease ¹, and also diabetes, dementia, Parkinson's disease and mobility problems ⁷.
• Pregnant people. The NHS and Santé publique France name them ⁷⁸; WHO/Europe says heat places an additional burden on them ².
• People on several medicines, or on medicines that make them react badly to heat ⁷. Santé publique France advises anyone on medication to ask a doctor or pharmacist ⁸.
• People who live alone, people who are homeless, and people who work outdoors or do manual labour ¹⁷.

The WHO says to check regularly on people over 65, people with heart, lung or kidney conditions, people with a disability and people who live alone ¹.

What are the signs of heat exhaustion and heatstroke?

Heat exhaustion comes first. Signs include heavy sweating, paleness, muscle cramps, tiredness, weakness, a fast or weak pulse, dizziness, headache, fainting, nausea and vomiting ⁴. The NHS also lists pale, clammy skin, a raised temperature and intense thirst ⁶. Santé publique France gives these warning signs: cramps, a fever above 38°C, unusual fatigue, headache, dizziness, nausea and confused speech ⁸.

Heatstroke happens when the body can no longer control its temperature. Sweating stops working and the body cannot cool down ³. It can cause permanent disability or death without emergency treatment ³. Ready.gov lists a body temperature above 103°F (39.4°C), red, hot and dry skin with no sweat, a rapid strong pulse, and dizziness, confusion or unconsciousness ⁴. The NHS adds fast breathing, seizures and loss of consciousness ⁶.

How do you cool someone down, and when do you call for help?

For heat exhaustion, the NHS gives four steps ⁶:

1. Move the person to a cool place.
2. Remove unnecessary clothing.
3. Give plenty of water. A sports drink or oral rehydration solution also helps replace salt.
4. Cool the skin: spray or sponge it with cool water and fan them. Wrapped cold packs under the armpits or on the neck also help.

The person should start to cool down and feel better within 30 minutes ⁶. Ready.gov says to call a healthcare provider if symptoms get worse or last more than an hour ⁴.

For heatstroke, call emergency services at once ⁴⁶. The NHS says to call 999 if someone is still unwell after 30 minutes of rest, cooling and fluids ⁶. While you wait, wrap the person in a cool, wet sheet, or fan them and sponge them with cold water ⁶. Ready.gov advises placing a cold, wet cloth or ice pack on the head, neck, armpits and groin, or soaking their clothing with cool water ⁴. If they lose consciousness, put them in the recovery position. Start CPR if they show no sign of life ⁶.

How do you keep your home cool?

• Block the sun by day, air the home at night. Close windows and cover them with blinds or shutters while it is hotter outside. Open them after dark when the outside air is cooler ¹⁷. Santé publique France also advises closing shutters by day ⁸.
• Cut indoor heat. Turn off as many electrical devices as possible ¹ and use the oven less ⁴.
• Cool your body directly. Take cool showers or baths and wet your skin with a damp cloth, a spray or wet clothing ¹⁴. Santé publique France advises wetting the body several times a day with light airflow ⁸.
• Find a cool place. The WHO recommends spending 2–3 hours a day somewhere cool ¹. If you have no air conditioning, Ready.gov says to find a cooling center, or places such as libraries and shopping malls ⁴.
• Drink before you are thirsty. The WHO suggests about 1 cup of water an hour and at least 2–3 litres a day ¹. The NHS advises avoiding alcohol, caffeine and hot drinks ⁷.
• Check room temperatures, especially where at-risk people live and sleep ⁷.
• Never leave a child, another person or an animal in a parked car, even briefly ¹⁴.

Do electric fans help?

The agencies disagree here. The WHO says to use electric fans only below 40°C (104°F), because above that a fan heats the body ¹. The NHS sets a lower limit: fans can help below 35°C ⁷. Ready.gov says not to rely on a fan as your main cooling. It says fans give a false sense of comfort but do not lower body temperature or prevent heat illness ⁴. With air conditioning, the WHO suggests setting the thermostat to 27°C (81°F) and adding a fan. It says this makes the room feel about 4°C cooler ¹.

What if the power goes out during a heatwave?

Heatwaves can cause power cuts ⁴. The WHO notes that power shortages during heatwaves can also disrupt hospitals, transport and water supply ¹. Without fans or air conditioning, the steps above that need no electricity matter most: shutters, night airing, water on the skin and drinking regularly ¹⁷⁸.

Ready.gov advises going to a community location with power if the heat is extreme ⁵. It says to plan ahead for power-dependent medical devices and refrigerated medicines. Ask your provider how long each medicine can be kept at higher temperatures ⁵. A closed refrigerator keeps food cold for about four hours, and a full freezer for about 48 hours ⁵. If the power is out for more than a day, throw away medicine that needs refrigeration unless the label says otherwise, and get a new supply ⁵. Use generators only outdoors, at least 20 feet (about 6 m) from windows, doors and attached garages ⁵.

What official agencies recommend

• WHO: stay out of the heat at the hottest times, block the sun by day and air the home at night. Fans only below 40°C, drink at least 2–3 litres a day, and check on vulnerable people ¹.
• WHO/Europe: older people, infants, outdoor workers and chronically ill people are particularly at risk, and heat adds a burden for pregnant women ².
• CDC (US): heatstroke is the most serious heat illness and needs emergency treatment ³.
• Ready.gov (US): know the signs of heat illness, find a cooling center if you have no air conditioning, and don't rely on fans ⁴. Plan for power outages ⁵.
• NHS (UK): stay in the shade between 11am and 3pm and keep living spaces cool. Fans only below 35°C. Call 999 for heatstroke ⁶⁷.
• Santé publique France: drink regularly, wet the body, close shutters by day, avoid alcohol and effort, and call 15 if someone is unwell ⁸.

Frequently asked questions

How much water should I drink in a heatwave?

The WHO suggests about 1 cup of water an hour and at least 2–3 litres a day ¹. Santé publique France says to drink regularly ⁸. Ready.gov says to drink plenty of fluids ⁴. If you take regular medication, Santé publique France advises asking your doctor or pharmacist for advice ⁸.

Is a fan enough to protect me?

Not always. The WHO says fans heat the body above 40°C ¹, and the NHS sets the limit at 35°C ⁷. Ready.gov says fans don't lower body temperature ⁴. The WHO and Ready.gov both recommend cool showers, wet skin and time in a cool place ¹⁴.

When should I open the windows?

Open them when it is cooler outside than inside, usually at night or early morning. Keep them closed, with blinds or shutters, during the hot part of the day ¹⁷⁸. The WHO and the NHS advise opening them after dark ¹⁷.

Can heat exhaustion be treated at home?

Usually yes, if the person cools down within 30 minutes of rest, cooling and fluids ⁶. If they are still unwell after that, or show signs of heatstroke, call emergency services ⁴⁶.

Next step: your household heat plan

Decide before the heat arrives who in your household is most at risk, where the nearest cool place is and how you will keep medicines during a power cut ¹⁵. Official advice differs by country, so write these decisions down for your household. See the Phaenyx plan.

Sources

1. World Health Organization (WHO) — Heat and health — https://www.who.int/news-room/fact-sheets/detail/climate-change-heat-and-health (accessed 2026-10-20)
2. WHO Regional Office for Europe — Heatwaves — https://www.who.int/europe/health-topics/heatwaves (accessed 2026-10-20)
3. Centers for Disease Control and Prevention (CDC) / NIOSH — Heat-related Illnesses — https://www.cdc.gov/niosh/heat-stress/about/illnesses.html (accessed 2026-10-20)
4. Ready.gov (U.S. Department of Homeland Security / FEMA) — Extreme Heat — https://www.ready.gov/heat (accessed 2026-10-20)
5. Ready.gov (U.S. Department of Homeland Security / FEMA) — Power Outages — https://www.ready.gov/power-outages (accessed 2026-10-20)
6. NHS (United Kingdom) — Heat exhaustion and heatstroke — https://www.nhs.uk/conditions/heat-exhaustion-heatstroke/ (accessed 2026-10-20)
7. NHS (United Kingdom) — Heatwave: how to cope in hot weather — https://www.nhs.uk/live-well/seasonal-health/heatwave-how-to-cope-in-hot-weather/ (accessed 2026-10-20)
8. Santé publique France — Heat Wave (Canicule) — https://www.santepubliquefrance.fr/en/info-accessible-to-all/heat-wave (accessed 2026-10-20)