You think you are beating the heat. You are drinking iced drinks, sitting under the fan, getting on with the day. And the heat is quietly winning anyway. The iced drink tastes like victory. Your core temperature has other ideas.
In the summer of 2022, the hottest season Europe had ever recorded, an estimated 61,672 people there died because of the heat. Italy lost the most, followed by Spain and Germany, and relative to their numbers, women died at a higher rate than men. It was not the first warning. The summer of 2003 brought more than 70,000 extra deaths across Europe, and countries drew up plans afterwards to protect the people most at risk. Nineteen years on, the toll was still in the tens of thousands. Those deaths did not make headlines the way a storm does. They happened one by one, over a few weeks of hot days and hot nights.
Heat is predictable and manageable. It is also easy to underestimate, which is how it does its damage.
How your body sheds heat
Your main cooling system is sweat, and sweat only cools you when it evaporates. Water turning to vapour on your skin carries heat away with it. Sweat that drips off or soaks into your shirt does very little. A soaked shirt is a sign of effort, not of cooling.
That is why humidity matters so much. In dry heat, sweat vanishes almost as fast as it appears, and you can lose a lot of water without noticing. In muggy heat, the air is already full of water, sweat has nowhere to go, and the cooling stalls.
There is a hard limit, and it comes sooner than was once thought. For years the point past which the body can no longer shed heat was put at a "wet-bulb" temperature of 35 °C, a single figure that combines heat and humidity. When young, healthy adults were tested doing light, everyday tasks, the heat outran their bodies at about 30.5 °C in humid conditions, and lower still in very hot, dry air. A muggy day can be more dangerous than the thermometer alone suggests.
Clothes decide the rest. Tight synthetic fabrics trap sweat against the skin, which is close to wearing a wetsuit in July. Loose linen and light cotton let air move and sweat evaporate. Light colours reflect the sun; dark ones soak it up. Black is slimming. It is also a solar panel.
Your body can learn the heat
The first hot days of a summer are the dangerous ones, because your body has not caught up yet. It is still dressed for spring.
Given repeated time in the heat, it adapts. You start sweating sooner and more freely, more blood goes to the skin to shed heat, your core temperature runs lower, your heart works less hard at the same task, and you hold on to fluid better. Across the tests of short heat training, a week or less of exposures was already enough to improve how people performed in the heat.
So ease into a heatwave. Go a little lighter on the first days, especially if you work or train outside, and build up as the week goes on.
Who is most at risk
Anyone can be harmed by heat. The NHS names the people most at risk.
Older people, especially those over 65. Babies and children aged five and under. People who are pregnant. People with long-term conditions, such as heart or breathing problems, diabetes, kidney disease, dementia or Parkinson's. People on several medicines, or on medicines that make hot weather harder to handle. People who live alone and may not be able to look after themselves. And people who work outside or exercise hard in the heat, such as runners, cyclists and anyone doing manual work.
Older people deserve a special mention, because their thirst fades with age just when they need it most. 7 Fun and Tasty Ways to Stay Hydrated Without the Boredom has why thirst is a poor alarm for a grandparent.
What to drink
Water is the base. Drink before you feel parched, and use the colour of your urine as the check: pale yellow is right, dark means drink more. Cold food and cold drinks are fine: the NHS recommends both in a heatwave.
When you are sweating a lot, salt matters as much as water. Sweat carries salt out of you, and water with a little salt, or a mug of salted broth, puts it back. What to Drink Instead of Plain Water, linked below, has why salt helps water stay in the body, and why the branded sports drink is mostly water with sugar.
Skip alcohol and caffeine in a heatwave. The cold beer in the sun is a lovely idea and a poor plan. The NHS advice is to avoid both. Alcohol makes the kidneys let water go, the opposite of what you need.
Water can be overdone too. On long, hot runs and walks, drinking far more than you sweat can drive the salt in your blood dangerously low. The hydration article above has the marathon runners it happened to.
Fans and the house
Fans help, up to a point. The NHS line is simple: electric fans can help if the temperature is below 35 °C. A fan does not cool the room. It cools you, by speeding up the evaporation of your sweat, and in a heat-balance model it raised the temperature people could tolerate by about 3 to 4 °C. Above that, the air is hotter than your skin and the fan blows heat at you as well as drying your sweat, so lean on other ways of cooling: a cool shower, wet clothes, a cooler room.
Put your hands in cool water. Twelve people aged 65 to 89 sat for two hours at 34 °C in humid air. When they dipped both hands and forearms in cool tap water for ten minutes, twice, their core temperature, skin temperature and heart rate rose more slowly than when they did not. A washing-up bowl of tap water on the table is the cheapest cooling device there is.
Keep the sun out by day. Close windows, curtains and blinds during the hottest part of the day, especially on the sunny side of the house. A room that never gets hot is easier than a room you have to cool.
Let the night in. Once the air outside is cooler than the air inside, open the windows, ideally on opposite sides of the house so a breeze can run through. A fan in a window, blowing out, helps pull the cool air in.
Know that the city runs hotter. Concrete, asphalt and buildings soak up heat by day and give it back at night. In the United States, cities run about 1 to 7 °F warmer than the countryside by day and 2 to 5 °F warmer at night, which is part of why hot city nights are so hard to sleep through. A in the bedroom tells you what you are actually dealing with, humidity included.
Air conditioning is not weakness. Over the 20th century, the death toll of very hot days in the United States, those averaging above 80 °F, fell by 75%. Almost all of the fall came after 1960, and the spread of air conditioning at home explains essentially all of it. If you or someone you care for is at high risk, one cool room in the house, or a few hours a day somewhere air-conditioned, is protection.
Sleeping in the heat
Heat in the bedroom costs sleep. It makes you wake more often and cuts the deep and dreaming stages, and humid heat makes it worse. 7 Ways to Make Every Day Work Better has the students in a Boston heatwave who slept in rooms without air conditioning and were about 13% slower on tests the next morning.
Let the night air in, as above, and hang a damp cloth in front of the open window: it cools the air as it comes through. Use a single cotton sheet, and a cool shower before bed.
Outside
Shade first, then a hat. Get out of direct sun, and when you cannot, wear a wide-brimmed hat; this has a UPF 50+ rating and a mesh band to let heat out. A long day out in strong sun is when sunscreen earns its place.
Wet things cool. A damp bandana around the neck or a works the same way sweat does, by evaporating, and it can be dipped again.
Pick the cooler part of the day. Run, walk, garden or work hard early in the day or in the evening, and keep the hottest hours for shade and rest. Southern Europe built a habit around it. 5 Ways to Harness Your Energy and Beat the Afternoon Slump has where the word siesta comes from.
The hot car
Never leave a child, an older person or a dog in a parked car, not even for a few minutes, and not even on a mild day.
On 16 clear, sunny days with outside temperatures of 72 to 96 °F, the inside of a dark car rose by about 40 °F within an hour. It climbed about 3 °F every five minutes, and 80% of the rise came in the first half hour. Even on the coolest day, the inside reached 117 °F. Opening the windows a crack made no difference. A parked car in the sun is an oven with seats.
When someone goes down
Heat illness comes in two stages, and the difference matters.
Heat exhaustion is the warning. The NHS lists tiredness, dizziness, a headache, feeling or being sick, heavy sweating with pale, clammy skin, cramps in the arms, legs or stomach, a high temperature, being very thirsty and feeling irritable.
If someone has it, the NHS gives four steps. Move them to a cool place. Take off unnecessary clothing such as a jacket or socks. Give them plenty of water to drink; a sports drink or rehydration solution helps replace the salt. Cool their skin: spray or sponge them with cool water and fan them, and put cold packs wrapped in a cloth under the armpits or on the neck. Never put ice straight on the skin. Stay with them. They should start to feel better within 30 minutes.
Heatstroke is the emergency. The signs are a very high temperature, hot skin that has stopped sweating, fast breathing and a fast heartbeat, confusion or restlessness, a fit, or passing out. Call 999, or your local emergency number, if you see any of these, or if someone with heat exhaustion is still unwell after 30 minutes of rest, cooling and drinking. Keep cooling them while you wait.
Cold water saves lives
There is an old warning that cold showers backfire in the heat, because the body supposedly fights back and heats itself up. The NHS advice is the opposite: a cool shower, or cool water on your skin or clothes, is one of the ways to cope. The cold shower was never the villain.
For heatstroke from exertion, cold water is the treatment. What decides survival is how fast the core temperature comes down, and putting the person in cold water is the gold standard. If there is no way to immerse them, keep dousing them with cold water without stopping. Cool first; the faster the better.
A manageable challenge
Heat is a predictable, manageable challenge. It kills when it is underestimated, when the first hot days catch people unprepared, and when nobody checks on the person living alone upstairs.
The defences are plain ones: shade, a hat, loose light clothes, water with a little salt, curtains by day and windows by night, and knowing the signs before you need them. Heat is patient. So is a good plan.
Before the next heatwave, pick one older neighbour or relative, and agree that you will check on them every hot day.
What should go in the glass on a hot day? What to Drink Instead of Plain Water — and What the Popular Alternatives Do to Your Body — the 13-drink test, why salt helps water stay in the body, and the drinks that cost more than they give.
Want to enjoy the long days, not just survive them? Fascinating Ways the Summer Solstice Can Boost Your Health and Happiness — what the longest day does for you, the small print, and why the hottest days are still to come.
Know someone who lives alone and would rather sweat than switch on a fan? Send them this, and ask if you can check in on the hot days.
Disclaimer: This article is general information. For advice about your own health, talk to a qualified health professional. Heatstroke is a medical emergency: call 999 or your local emergency number.
Affiliate Disclosure: This article contains affiliate links. As an Amazon Associate, All For Life earns from qualifying purchases, at no extra cost to you. We only link to products we would recommend without the commission.
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