Heat exhaustion and heatstroke
The body cools itself in two ways: by sending blood to the skin and by evaporating sweat. In hot weather both mechanisms run at full stretch, and sooner or…
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The body cools itself in two ways: by sending blood to the skin and by evaporating sweat. In hot weather both mechanisms run at full stretch, and sooner or later comes the moment when they cannot keep up. First a person feels faint, weak and generally awful — that is heat exhaustion, and it almost always resolves within half an hour. If no help arrives, body temperature keeps climbing and the picture turns into heatstroke, which is a situation counted in minutes. The difference between the two is the single most important thing to take away from this page, so we start there.
How exhaustion differs from heatstroke
In heat exhaustion the cooling system is still working, it simply cannot keep pace. The person sweats heavily, the skin is damp and pale, they feel dreadful — but they are conscious, they know where they are and they answer coherently. Move them somewhere cool, give them a drink, and within twenty to thirty minutes they will be noticeably better.
In heatstroke the cooling system has given up. Body temperature rises above forty degrees and, at the same time, behaviour or consciousness changes: the person slurs or muddles their words, does not know where they are, acts oddly or aggressively, falls asleep and cannot be roused, or has a seizure. It is the combination of extreme heat and altered mind — not the heat alone — that separates heatstroke from exhaustion. At that temperature the cells of the brain, liver, kidneys and muscle begin to be damaged, and the longer it lasts the more of that damage becomes permanent.
One important correction to the common picture: in heatstroke the skin is not necessarily dry and burning. That is what happens to an older person overheating at home in a closed flat. A young person who has overheated at training or on a building site often carries on pouring with sweat — and that should reassure nobody. Judge by the head, not by dry skin.
The signs that give overheating away
Heat exhaustion starts vaguely and is easy to put down to tiredness:
- weakness, listlessness, legs that feel like cotton wool;
- dizziness, vision darkening, headache;
- nausea and sometimes vomiting;
- heavy sweating, with skin pale, clammy and cool to the touch;
- strong thirst, dry mouth, urine scanty and dark;
- cramps in the calves, thighs and abdomen;
- a fast pulse and rapid breathing;
- irritability — in children this is sometimes the only early sign; they simply turn grizzly and stop playing.
In very young children and in older people the picture is thinner still: a baby goes floppy, feeds poorly and has a dry nappy, while an older person becomes drowsy and slow. In both cases it looks from the outside less like overheating and more like "something is not right", which is exactly why in hot weather these people need visiting and touching, not phoning to ask whether they are all right.
What to do in the first half hour
The steps are simple, and they should be taken at once rather than waiting to see whether it passes.
- Get the person out of the heat — into shade, indoors, or into an air-conditioned car.
- Lie them down and raise their legs.
- Take off surplus clothing and shoes and loosen anything tight.
- Cool the skin: wet it with cool water, spray it, wrap the person in a damp sheet and fan them. Ice packs wrapped in cloth go on the neck, in the armpits and in the groin, where blood vessels run close to the surface.
- If they are fully alert, give a drink — cool water, or better a drink containing salts if they have sweated a lot. Small sips, often, not a whole glass at once.
- Stay with them until they improve, and keep an eye on their speech and behaviour.
What not to do: do not give drinks to anyone who is confused, drowsy or vomiting — the fluid will go into the airway. Do not rub the skin with alcohol. Do not give fever medicines: in overheating they do nothing, because here the temperature has not risen from inflammation but from heat piling in from outside. And do not give salt tablets.
After half an hour the person should be clearly better. If there is no improvement, treat it as heatstroke and call an ambulance.
When it is heatstroke and an ambulance is needed
Call an ambulance (in Europe, the single number 112) if someone who has overheated has:
- confused speech, strange behaviour, failure to recognise familiar people or to know where they are;
- excessive drowsiness that is hard to rouse them from, or loss of consciousness;
- a seizure;
- a very high body temperature;
- hot, flushed skin that has stopped sweating;
- fast shallow breathing, breathlessness, a fast or irregular pulse;
- vomiting that makes drinking impossible;
- had thirty minutes of rest in the cool, with fluids and cooling, and is no better.
While the ambulance is on its way, do not stop cooling — that is the main treatment, and started on the spot it saves more than anything else. Undress them, pour cool water over them, fan them, apply ice through a cloth. If the person is unconscious but breathing, turn them onto their side so that they cannot choke on vomit. Do not try to drive them yourself: on the way you will be able neither to cool them nor to watch their breathing.
Who overheats sooner than others
The risk is not spread evenly, and most households contain someone who needs watching in a hot spell:
- babies and children up to three or four: they sweat less efficiently than adults and cannot take themselves into the shade or ask for water;
- older people, especially those living alone: with age thirst is felt less keenly and blood vessels respond more sluggishly to heat;
- people with heart, lung or kidney disease, with diabetes, or carrying excess weight;
- people taking diuretics, blood pressure drugs, certain antidepressants, antipsychotics and medicines with a drying effect — many of these reduce sweating or the amount of fluid in the body;
- people working or training in the heat, particularly in the first days: the body needs a week and a half or two to adjust to a new climate or to the start of summer;
- anyone already feverish from an infection, unwell with a stomach upset or hungover: they meet the heat dehydrated to begin with.
And one line that cannot be repeated too often: a child must never be left in a closed car, not even for five minutes, not in the shade and not with a window cracked open. The interior heats up faster than people expect, and heatstroke in a child develops within minutes. The same goes for animals.
How to avoid getting there at all
Everything that helps is well known and dull, but during a hot week it works better than any medicine.
- Drink regularly rather than waiting for thirst. A simple guide is the colour of your urine: pale means you have enough fluid, scanty and dark means it is time to drink.
- Plan walks, sport and outdoor work for early morning and evening, and spend the hottest hours in the shade or indoors.
- Wear light, loose, pale clothing, cover your head and use sun cream: burnt skin sheds heat less well.
- Go easy on alcohol — it dehydrates and blunts your sense of overheating. Strong coffee is not the best choice in the heat either.
- At home, close curtains and windows on the sunny side during the day, ventilate at night, and switch off equipment that gives off heat. A fan helps while the air is not too hot; if the room is nearing forty degrees, a few hours somewhere air-conditioned is more use.
- Eat your water as well as drinking it — vegetables, fruit, soups. Salt from ordinary food covers what is lost in sweat, and separate salt supplements are not needed.
- During long exertion in the heat, drink something containing salts and not only plain water: hours of nothing but water leave too little salt in the blood, and that state carries a danger of its own.
- If you are travelling somewhere hot or starting a training season, build up gradually and take the first days at half effort.
And go and check on the people who will not complain: elderly relatives, neighbours living alone, small children. One ring on the doorbell in the middle of a heatwave is sometimes worth more than everything else on this list.
Online consultation
A remote appointment handles everything around overheating rather well, both before and after. The doctor can help work out what actually happened yesterday if someone felt ill in the heat and whether any after-effects are likely; go through which of your regular medicines are tolerated less well in hot weather and what to raise with your own doctor before summer or before a trip somewhere hot; and advise on how to organise fluid intake in heart or kidney disease, where "drink more" is a poor instruction on its own. It is also the place to talk about training safely in the heat and about caring for an elderly relative through a hot spell. What cannot be dealt with on a screen is the episode itself with altered consciousness, seizures or a very high temperature: that is an ambulance, with no discussion.
This material is for information only and does not replace medical advice.
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