Too Hot on Holiday? Heat Exhaustion, Heat Stroke and What to Do

Why this happens to travellers in particular

The CDC chapter this article is based on makes a point that is easy to miss: heat illness is most often seen in workers, soldiers and athletes, but travellers get it because many of the most popular destinations are hot, and because people arrive from cooler climates, unfit and not acclimatised, and then do more than they would at home. Sitting on a beach or doing a short walking tour carries minimal risk. Hiking, cycling or a long day on foot in the heat does not.

Two things raise the risk more than anything else. The first is dehydration, which CDC calls the most important predisposing factor apart from the weather and the effort itself. The second is acclimatisation: the body adapts to heat over roughly ten days of daily exercise in it, and visitors in their first week have not had that time. CDC also lists the conditions that limit heat tolerance: cardiovascular disease, diabetes, kidney disease, certain medications, skin conditions or scarring that limit sweating, very young or old age, high body mass and a current infection.

Heat exhaustion: what it looks like and what to do

According to CDC, most people who feel unwell during or after exertion in the heat, or who cannot keep going, have heat exhaustion. The presumed cause is loss of fluid and salts. Mental changes such as irritability, confusion or irrational behaviour can be present; body temperature can be normal or mildly raised. It can also build over several days in someone not used to the heat, and is often mistaken for a summer flu: weakness, fatigue, headache, dizziness, loss of appetite, nausea, vomiting and diarrhoea.

CDC's treatment is simple and works: lie down in the shade or somewhere cool, rest, and drink water or fluids that contain some glucose and salt. Most people cool spontaneously and recover within hours. The chapter gives a recipe travellers can make themselves: a quarter to half a teaspoon of table salt in a litre of water, with a few teaspoons of sugar or some orange or lemon juice for taste. Commercial sports drinks work too, and so does plain water with salty snacks.

Heat stroke: the emergency

Heat stroke is the one form of heat illness where the body has stopped being able to bring its own temperature down. CDC describes it as a medical emergency requiring aggressive cooling and hospital care, because uncontrolled high temperature and circulatory collapse damage the brain, kidneys, liver and heart. It can come on acutely in a fit person exercising hard in the heat, usually still sweating heavily, or gradually over days in someone chronically ill who has simply been too hot.

The early symptoms overlap with heat exhaustion: confusion or a change in personality, loss of coordination, dizziness, headache, nausea. The difference is progression and degree. CDC's field definition is a body temperature of 41°C or more with marked mental change such as delirium, convulsions or coma; and it adds that even without a thermometer, someone with heat stroke will feel hot to the touch. Many complications happen in the first 24 to 48 hours, which is why hospital is the destination.

The trap: drinking too much water

CDC gives this its own section because it catches people who are trying to do the right thing. Over long exertion, drinking large volumes of plain water can push blood sodium too low. The early symptoms look exactly like heat exhaustion: loss of appetite, nausea, vomiting, headache, weakness, lethargy. The clues CDC gives are that mental changes persist or appear without a raised temperature, that major symptoms come on late or even after stopping, and that the person has been drinking a lot of water. The chapter calls the old advice that you cannot drink too much outdated and dangerous.

The prevention is to drink enough to relieve thirst, not more; and on long days in the heat, six hours or more, to take in salt, which CDC says is best done with food: salty snacks such as crackers, pretzels or trail mix rather than salt tablets, which often cause nausea. Most sports drinks do not contain enough sodium on their own for this.

Preventing it in the first place

• Lightweight, loose, light-coloured clothing that lets air circulate, and a wide-brimmed hat, which CDC says markedly reduces radiant heat.
• Drink during exertion; thirst alone is not a reliable guide for mild dehydration, but forcing water on someone who is not thirsty raises the risk of low sodium. For short or moderate effort plain water is as good as electrolyte drinks.
• Salt from food on long days, not tablets. Checking urine colour and volume is most accurate in the morning.
• Do less in the first week. CDC advises limiting the intensity and length of exercise during the first week of travel and avoiding strenuous activity in the hottest part of the day, which is what local people do.

You are already there: what this means in practice

Everything above is the CDC chapter. This section is ours. If you are reading this in a hotel room in Egypt, Morocco, Malta or the Dominican Republic in summer, the practical points are these. First, the summer flu pattern is common: two or three days of feeling rotten, headachy, off your food, a bit of diarrhoea, in someone who has been walking in 35 degree heat. Shade, rest and salty fluids are what CDC describes for heat exhaustion, and they are also a useful test: if you are better in hours, that was probably it.

Second, the countries we write about change the next step. In Egypt, TravelHealthPro lists heat among the risks for everyone and advises a priority on hydration and shade in desert areas; hotels will offer a doctor to your room, and FCDO's caution about that is on our Egypt guide. In Morocco, pharmacies are open round the clock in every city, which matters for rehydration salts at night; the route from there is on our Morocco guide. In Malta, you can see a private GP at most pharmacies, and 112 reaches an ambulance: see our Malta guide. In the Dominican Republic, tap water is not drinkable, so rehydrate with bottled water; resorts send doctors and the private hospitals are expensive, which is covered on our Dominican Republic guide. In France, 15 reaches the SAMU for a medical emergency such as heat stroke, and the pharmacie de garde, the duty pharmacy, covers nights, Sundays and public holidays; see our France guide.

What a video doctor can and cannot do about this

Honestly stated. A video consultation is one option for the grey zone: you are unwell in the heat, you cannot tell whether this is a day in the shade or something more, and you would like a clinician to look at you and ask the questions that matter. A doctor can see how you look and talk, ask how much you have drunk and whether you are passing urine, check for the mental changes CDC describes, tell you whether to rest and rehydrate or to be seen, and say what to watch for over the next hours. For an older traveller, a child, or someone with one of the conditions CDC lists, that judgement is worth more.

A video consultation cannot take a temperature, cannot cool anyone down, and cannot treat heat stroke; nothing on this page should delay emergency care if that is what the situation needs. If the person is confused, has collapsed, is having a seizure, or feels hot to the touch, CDC's guidance is emergency services and cooling without delay; a video consultation is not a substitute for that, and we would rather say so here than have anyone find out later.