Learn what to do during a heatwave, from hydration and cooling to recognizing heatstroke. Practical, official guidance for families, workers, and pet owners in France.
When temperatures spike and stay high for days at a time, knowing exactly what to do during a heatwave can make the difference between mild discomfort and a genuine medical emergency. Extreme heat doesn't just affect older adults or people with health conditions. It can affect anyone, including fit, healthy adults who overestimate how much heat their body can handle. This guide covers the practical steps to take before, during, and after a heatwave, how to recognize the warning signs of heat-related illness, and how to protect the people and pets who depend on you.
According to Météo-France, a heatwave, or canicule, refers to a period of very high temperatures, both day and night, lasting at least three days, that is likely to pose a health risk, particularly for fragile or overexposed people. This is distinct from a heat peak, a brief episode of one to two days with temperatures well above seasonal norms.
Heatwaves are no longer rare events. France now averages 12 canicule days per year over the last decade, compared to just 3 days in the 1980s, and the trend is accelerating. Under current climate projections, the number of heatwave days in France is expected to multiply by five by 2050 and by ten by 2100.
Extreme heat forces the body to work harder to regulate its internal temperature. The World Health Organization explains that heat is an important environmental and occupational health hazard, and can worsen underlying illnesses including cardiovascular disease, diabetes, mental health conditions, and asthma, while increasing the risk of accidents. Left unmanaged, rising body temperature and fluid loss during a heatwave can progress from mild heat stress to dehydration and, in severe cases, heatstroke, a medical emergency with a high case-fatality rate.
Understanding why heatwaves are dangerous is only the first step. To explore the science behind extreme heat, learn why heatwaves are becoming more frequent in France, discover who is most at risk, and find detailed guidance on prevention, official alert systems, first aid, and protecting pets, read our comprehensive guide on How to Stay Safe in Heatwaves and Extreme Heat. It provides a broader overview of heatwave safety and practical advice to help you prepare before temperatures rise.
Quick answer: What should you do during a heatwave?
Drink water regularly throughout the day, without waiting until you're thirsty
Close windows and shutters during the day, open them at night when it's cooler
Avoid going outside during peak heat hours, generally early to mid-afternoon
Wear lightweight, loose, light-colored clothing
Use fans and misting sprays together, and cool your face and forearms often
Eat light, water-rich meals and avoid alcohol
Limit physical exertion and reschedule strenuous activity for cooler hours
Follow official Météo-France heatwave alerts for your area
Drink water at regular intervals rather than waiting until you feel thirsty, since thirst is often a late signal of dehydration. Avoid alcohol, which accelerates fluid loss, and limit caffeinated or sugary drinks.
Close windows and shutters during the day to block out heat, and open them in the evening and overnight when outside temperatures drop, to let cooler air circulate through your home.
Try to schedule errands, exercise, and outdoor tasks for the early morning or evening, and avoid being outside during the hottest part of the afternoon.
Choose loose, light-colored clothing made from breathable fabrics like cotton, which allow air to circulate and help sweat evaporate.
Use fans and misting sprays together for maximum cooling effect, and refresh your skin, especially your face and forearms, several times throughout the day.
Favor meals with high water content, and eat regularly and in sufficient quantity, since food also plays a role in maintaining hydration and electrolyte balance, as outlined by Santé publique France.
Reduce the intensity and duration of physical effort during heatwave conditions. If activity is unavoidable, wetting your clothing beforehand and letting it dry on your skin provides additional cooling.
Check the Météo-France vigilance map regularly during a heatwave, and adjust your plans according to the alert level in your department.
|
Do |
Don't |
|
Drink water regularly, before you feel thirsty |
Wait until you're thirsty to drink |
|
Keep children and pets with you or in cool, shaded areas |
Leave children or pets in a parked vehicle, even briefly |
|
Reschedule exercise for cooler hours |
Exercise or work hard during peak temperatures |
|
Choose water or non-alcoholic drinks |
Drink excessive alcohol, which speeds up dehydration |
|
Wear light, loose, breathable clothing |
Wear dark or heavy clothing that traps heat |
|
Act quickly on early symptoms |
Ignore headaches, dizziness, or nausea |
Painful muscle spasms, often in the legs or abdomen, caused by fluid and electrolyte loss during exertion in the heat.
Heavy sweating, weakness, dizziness, nausea, headache, and cool, clammy skin. This is your body signaling that its cooling system is under strain.
The WHO identifies heatstroke as a medical emergency with a high case-fatality rate. It involves a very high body temperature, confusion, slurred speech, hot and often dry skin, and can lead to loss of consciousness.
|
Heat Exhaustion |
Heatstroke |
|
|
Body temperature |
Normal or mildly elevated |
Very high, often above 40°C |
|
Skin |
Cool, pale, clammy |
Hot, dry or minimally sweating |
|
Mental state |
Tired, dizzy, irritable |
Confused, disoriented, unconscious |
|
Pulse |
Fast, weak |
Fast, strong |
|
Action needed |
Rest, cooling, fluids |
Call emergency services immediately |
Call for help immediately if someone shows confusion, slurred or incoherent speech, a very high fever, or loses consciousness during a heatwave. In France, dial 15 for medical emergencies or 112 for the general European emergency number.
|
Group |
Why They're at Higher Risk |
|
Older adults |
Reduced ability to regulate body temperature, often combined with medications that affect hydration |
|
Babies and young children |
Immature thermoregulation and higher surface-to-body-weight ratio |
|
Pregnant women |
Increased cardiovascular demand |
|
People with chronic conditions |
Heart, kidney, respiratory, or mental health conditions can be worsened by heat |
|
Outdoor workers |
Heat combined with physical exertion and reduced alertness |
|
Athletes |
High exertion raises core body temperature and fluid loss quickly |
Heat-related mortality among people over 65 increased by approximately 85% between 2000-2004 and 2017-2021, according to the WHO, underscoring just how disproportionately extreme heat affects older adults.
Close shutters and windows during the day, open them at night, and avoid adding indoor heat sources like ovens or unnecessary electronics during peak hours.
Since 1 July 2025, French law requires employers to take specific action during heat alerts. Under Décret n° 2025-482, once a Météo-France yellow, orange, or red alert is triggered, employers must evaluate heat-related risks, adapt work organization and hours, provide rest periods, and ensure workers have access to at least three liters of cool drinking water per day where running water isn't available. Full requirements are detailed by economie.gouv.fr.
Check the heatwave alert level for your destination before traveling, keep water on hand during transit, and avoid scheduling demanding activities during the hottest hours of the day.
Supervise children constantly near water, check conditions before swimming, choose supervised swimming areas where possible, and avoid alcohol before any water activity, as recommended by French civil security authorities.
Move workouts to the early morning or evening, reduce intensity, and increase water intake before, during, and after exercise.
Move the person to a cool, shaded area, have them lie down with their legs slightly elevated, offer small sips of water, and cool their skin using damp cloths or a fan.
Call emergency services immediately. While waiting for help, move the person out of direct heat and begin cooling their body, focusing on the neck, armpits, and groin, where blood vessels sit close to the skin.
Never give fluids to someone who is confused or losing consciousness, since this creates a choking risk, and never leave a person showing signs of heatstroke unattended while waiting to see if symptoms pass on their own.
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Learn More →Close shutters, blinds, or curtains on sun-facing windows during the day, and reopen them at night to let cooler air in.
Create cross-drafts where possible by opening windows on opposite sides of your home during cooler hours, but keep them closed once outdoor temperatures rise again.
Limit the use of ovens, and other heat-generating appliances during the hottest part of the day, and consider reducing pollution sources indoors, such as air fresheners or tobacco smoke, which can add strain during hot, stagnant conditions.
Heatwaves can put pressure on electricity grids due to rising cooling demand. Keep a battery-powered fan, flashlight, and a stock of water on hand in case of an outage.
Dress infants and young children in light clothing, offer fluids frequently, and never leave them alone in a parked vehicle, even for a short time.
Check in regularly on elderly or isolated relatives and neighbours, and encourage them to register with their local town hall in France, where vulnerable residents can be added to a list so aid and rescue teams can check on them during heatwaves.
Animal welfare during periods of climate stress is a recognized concern for organizations like the World Organisation for Animal Health (WOAH), which works globally on animal health and welfare standards. Practical steps include:
Keep fresh, cool water available at all times
Walk dogs during the coolest parts of the day and avoid hot pavement
Watch for excessive panting, drooling, lethargy, or collapse, and see a vet immediately if these occur
Never leave a pet in a parked car, even briefly, even with the windows cracked
Météo-France uses a four-level color-coded vigilance system:
Green – no particular vigilance needed
Yellow – heat peak, one to two days of intense heat posing a risk to fragile populations
Orange – canicule, intense heat meeting departmental thresholds for three consecutive days and nights
Red – extreme canicule, exceptional in duration, intensity, and geographic extent, with major health impact
Check the Météo-France vigilance map daily, updated at least twice a day, or subscribe to alert notifications through the Météo-France app for your department.
France also runs a dedicated toll-free hotline, Canicule info service, at 0 800 06 66 66, generally available from 9am to 7pm, offering guidance on protecting yourself and those around you, according to Service-Public.fr.
A heatwave can quickly escalate into a period of extreme heat, where prolonged high temperatures significantly increase the risk of heat-related illness. If severe weather warnings have been issued or conditions become exceptionally hot, our guide What to Do During Extreme Heat explains the immediate actions to take, how to recognize warning signs that require urgent medical attention, and the best ways to protect children, older adults, outdoor workers, and pets during dangerous heat conditions.
|
Myth |
Fact |
|
Fans always prevent heatstroke |
Fans help but have limitations in extreme heat, and work best combined with misting or cool water |
|
You only need water when you're thirsty |
Thirst is often a late sign of dehydration |
|
Only older adults are affected |
Anyone can experience heat-related illness, regardless of age or fitness |
|
Cloudy weather means there's no risk |
Heat stress can still occur on cloudy or humid days without direct sun |
Knowing what to do during a heatwave comes down to a few consistent habits, repeated daily until the alert passes. Stay hydrated before you feel thirsty, keep your living space cool, avoid unnecessary exposure during the hottest hours, and watch for early symptoms of heat-related illness in yourself and those around you. Pay particular attention to older adults, young children, and pets, who often can't regulate their own exposure to heat as effectively as you can. Following official Météo-France alerts and acting quickly if conditions worsen can make all the difference.
Small daily adjustments, made early, go a long way toward reducing the health risks of extreme heat. Share this guide with family, neighbours, or coworkers before the next heatwave arrives.
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