How to protect your health during extreme heat: a complete prevention guide

Heat waves are among the most dangerous weather phenomena for human health. According to the World Health Organization, extreme heat causes thousands of premature deaths across Europe every year, and climate projections indicate these episodes will become more frequent, more intense and longer-lasting in the coming decades.

The good news is that most serious heat-related effects are preventable with the right information and habits. This guide compiles recommendations based on public health and meteorological service guidelines.

What is a heat wave?

There is no universal definition, but in Spain AEMET defines a heat wave as an episode of at least 3 consecutive days during which a significant percentage of weather stations record maximum temperatures above the 95th percentile of their historical series (July–August).

In practical terms, this translates to temperatures exceeding 40 °C inland, 35–38 °C along the Mediterranean coast and 30–33 °C in the northern Atlantic coast, accompanied by tropical nights (minimums above 20 °C) that prevent the body from recovering.

Hydration: the first line of defence

• Drink at least 2–2.5 litres of water a day, even if you don't feel thirsty. Thirst sets in when the body has already lost 1–2% of its water.
• Avoid alcohol: it is a diuretic and speeds up dehydration. A beer "to cool down" is actually counterproductive.
• Cut back on caffeine: coffee and energy drinks increase urinary frequency.
• Mineral-salt drinks: if you sweat heavily (sport, outdoor work), add a pinch of salt to water or use isotonic drinks. Intense sweating strips away sodium and potassium.
• Cool water, not ice-cold: very cold drinks can cause a gastric spasm and slow absorption.
• Always carry a water bottle: in the car, in your bag, on your desk. If you can't see it, you won't drink it.

Eating for the heat

• Light, frequent meals: five small meals are better than two large ones. Heavy digestion generates internal heat.
• Fruit and vegetables with high water content: watermelon (92% water), melon, cucumber, tomato, lettuce, strawberries.
• Gazpacho and cold soups: they hydrate, supply minerals and are easy to digest.
• Avoid very hot, fried or heavily spiced food during the hottest hours.
• Watch food safety: heat accelerates bacterial growth. Don't break the cold chain. Eat salads and cold dishes freshly prepared.

At home: how to keep things cool

• Close shutters and windows from early morning until sunset. The goal is to keep heat out.
• Ventilate at night and first thing in the morning (before 9:00 AM), creating a cross-draught if possible.
• Awnings and thermal curtains: they can lower indoor temperature by 5–10 °C.
• Use fans wisely: a fan does not cool the air—it moves warm air. It is more effective if you place a bowl of ice in front of it, or run it with windows open at night.
• Air conditioning at 25–26 °C: each degree lower means roughly 7% more energy consumption. 25 °C is comfortable enough.
• Find the coolest room in the house: usually the north-facing one, and use it for resting.
• Use cotton or linen bedsheets, not synthetic fabrics.

Outdoors: basic protection rules

• Avoid sun exposure between 12:00 and 17:00: this is when UV radiation and temperature peak.
• If you must go out: wear a wide-brimmed hat, loose light-coloured clothing (white reflects more heat), and sunglasses.
• SPF 50+ sunscreen: apply 30 minutes before going outside and reapply every 2 hours (or after heavy sweating).
• Seek shade: walk on the shaded side of the street, rest under trees, use a parasol.
• Never leave people or animals in a parked car: the interior can reach 60 °C within 20 minutes, even with windows slightly open.

Exercise and physical activity in the heat

• Train early (before 9:00 AM) or in the evening (after 8:00 PM).
• Reduce intensity by 20–30% compared to your usual level. Performance drops in the heat and pushing through is dangerous.
• Hydrate before, during and after: drink 500 ml in the hour beforehand, 150–200 ml every 15–20 minutes during exercise, and rehydrate afterwards with water or an isotonic drink.
• Breathable technical clothing: it helps sweat evaporate, which is the body's main cooling mechanism.
• Know the warning signs: dizziness, nausea, cramps, confusion → stop immediately, seek shade and drink.
• If you run or cycle, carry your phone and tell someone your route.

High-risk groups

Heat stroke: how to recognise it and act

Heat stroke is a medical emergency. It occurs when the body loses its ability to regulate its temperature, which rises above 40 °C. Without treatment it can be fatal.

Warning signs

• Very high body temperature (>39.5 °C)
• Hot, red and dry skin (no longer sweating)
• Severe headache, dizziness, confusion
• Nausea, vomiting
• Rapid, strong pulse
• Loss of consciousness

What to do (first aid)

• Call emergency services immediately (112 in Europe, 911 in the US).
• Move the person into shade or a cool place.
• Cool the body: apply cold wet cloths to neck, armpits and groin; spray with water; fan them.
• Do not give fluids if the person is unconscious (aspiration risk).
• Place the person on their side (recovery position) if they vomit or lose consciousness.
• Do not use antipyretics (paracetamol/ibuprofen): they do not work in heat stroke.

Tropical nights: how to sleep in the heat

When the night-time temperature stays above 20 °C (tropical night) or 25 °C (torrid night), falling asleep becomes a challenge:

• Take a lukewarm shower before bed (not cold: the body reacts by generating more heat).
• Lightly dampen the bedsheet or place a damp towel over your body.
• Fan blowing nearby, but not directly at your face (it can dry out your throat and eyes).
• Have a light dinner at least 2 hours before bedtime: digestion generates heat.
• If you use A/C, set a timer to switch off after 2–3 hours; running it all night can cause stiffness and dryness.

Pets and extreme heat

• Fresh water always available, in several spots around the home.
• Never leave an animal in the car.
• Short walks first thing and last thing. Check the pavement: if it burns your hand, it burns their paw pads.
• Signs of heat stroke in dogs: excessive panting, very red gums, staggering, vomiting. Cool with lukewarm water (not ice-cold) and take the dog to the vet.

Frequently asked questions

Exactly how much water should I drink?

The general recommendation is 2–2.5 litres a day, but during extreme heat with heavy sweating this can rise to 3–4 litres. Older adults, athletes and outdoor workers need more. Urine colour is a good indicator: it should be pale yellow.

Is a fan dangerous above a certain temperature?

Yes. Above 35 °C a fan can be counterproductive: it blows air hotter than your skin and accelerates dehydration without cooling you. In that case, it is better to wet the skin or use air conditioning.

Is it true that dark clothing makes you hotter?

Yes. Dark colours absorb more solar radiation. The ideal clothing in extreme heat is light-coloured, loose-fitting and made of natural fabrics (cotton, linen).

Where can I check heat warnings?

In Spain, AEMET publishes heat-wave warnings on its website and through the National Preventive Action Plan for High Temperatures issued by the Ministry of Health. At Meteo.es we display active warnings in our alerts section.

Sources: World Health Organization (WHO), Spanish Ministry of Health, AEMET, Red Cross, Spanish Society of Emergency Medicine (SEMES).