Overview
Heat illness happens when the body cannot lose heat as fast as it gains it. Heat exhaustion is the earlier, milder stage: the person feels unwell but thinks clearly, and usually recovers within about thirty minutes of being cooled and given fluids.
Heat stroke is the dangerous stage. The temperature climbs to around 40C (104F) or higher and the brain is affected, so the person becomes confused, slurs words, has a fit or collapses. The skin may be hot and dry, or still sweaty. It can cause lasting damage or death.
Symptoms
Heat exhaustion usually brings:
- Tiredness, weakness and irritability
- Headache and dizziness
- Feeling sick or being sick
- Heavy sweating, with pale, clammy skin
- Cramps in the arms, legs or tummy
- Strong thirst and passing less urine
Signs that it has become heat stroke:
- Confusion, restlessness or strange behaviour
- Slurred speech
- A fit, fainting, or not waking up
- A very high temperature with hot skin, dry or sweaty
- Fast breathing and a racing heartbeat
When to see a doctor
See a doctor in the next few days if heat exhaustion keeps returning on ordinary days, if muscle pain and weakness last after working in the heat, or if you feel faint in the heat while taking medicines for or the heart.
Causes
Heat illness comes from high temperature and humidity together. Sweat is the body's cooling system, and when the air is hot and damp, sweat does not evaporate well and the body keeps heating up.
It builds up faster during heavy work or exercise, when there is too little to drink, in closed unventilated rooms, and inside parked vehicles, which heat up very quickly.
Risk factors
- Babies and young children, and people over 65
- Outdoor work: farming, construction, road work, deliveries
- Heart disease, diabetes, kidney disease or obesity
- Water tablets, medicines and some other prescriptions
- Alcohol
- Already being dehydrated, or unwell with fever or diarrhoea
- Not being used to the heat, for example in the first days of a heat wave
Complications
A body that stays overheated can be injured in several places at once: the brain, the heart, the kidneys and the muscles. Muscle breakdown shows as severe muscle pain with dark, tea coloured urine and can damage the kidneys.
Without quick cooling and treatment, heat stroke can cause permanent disability or death, which is why the minutes before reaching hospital matter so much.
Prevention
- Stay out of the sun between 11am and 3pm on hot days
- Drink water through the day, before thirst sets in
- Wear light, loose, light-coloured clothes, and cover the head outdoors
- Take rest breaks in the shade during outdoor work, and build up gradually
- Keep rooms cool and shaded, and check on elderly neighbours and relatives
- Go easy on alcohol and on heavy exercise in the hottest hours
- Never leave a child, an older person or a pet inside a parked vehicle
Diagnosis
Heat stroke is recognised from the history and the examination: time spent in the heat, a high measured body temperature, and a change in how alert or sensible the person is.
In hospital, blood and urine tests check the salts, the kidneys and the muscles, and other causes of a high temperature and confusion, such as infection, are looked for.
Treatment
The treatment is rapid cooling, begun where the person is found. Call for emergency help, then:
- Move them into shade or a cool room and remove outer clothing
- Wet the skin with cool water and fan them, or use a cold water or ice bath if one can be arranged
- Put cold packs, wrapped in cloth, on the neck, armpits and groin
- If they are fully awake, give cool water or an oral rehydration drink in small sips
- If they are drowsy or being sick, give nothing by mouth and lay them on their side
In hospital, cooling continues with monitoring of the temperature, and fluids are given into a vein. The kidneys, muscles, clotting and breathing are watched, and any organ that has been injured is supported while the body recovers.
Myths and facts
Things people often say about this. Open each one to see what is true.
Myth“If the person is still sweating it cannot be heat stroke.”What is true?
Fact
Skin in heat stroke may be hot and dry, but it can also be soaked in sweat, especially when the person has been working or exercising. What marks heat stroke is the very high temperature together with confusion, a fit or loss of consciousness, not whether the skin is wet.
Myth“Give paracetamol or aspirin to bring the temperature down.”What is true?
Fact
Fever medicines work on fever caused by illness, not on a body that has been overheated from outside. Guidance for heat emergencies is not to give them, and to lower the temperature by cooling the body instead.
Myth“Cold water and ice are dangerous, so only lukewarm water should be used.”What is true?
Fact
For heat stroke, cooling fast matters most. A cold water or ice bath is recommended where it can be arranged, and otherwise wetting the skin with cold water, fanning, and cold packs on the head, neck, armpits and groin.
Myth“Pour water into the mouth of someone who has collapsed in the heat.”What is true?
Fact
Anyone who is unconscious, drowsy or being sick should be given nothing by mouth, because the drink can go into the lungs. Cool them from the outside, lay them on their side and wait for emergency help.
Questions to ask your doctor
Tick the ones you want answered and take them with you.
Common questions
How do I tell heat exhaustion from heat stroke?
Look at the mind, not only the skin. In heat exhaustion the person feels awful but can talk to you sensibly and improves as they cool down. In heat stroke the temperature is very high and the brain is affected, so they are confused, speak strangely, have a fit or cannot be woken. That is an emergency.
Should I give salt water or an oral rehydration drink?
For someone who is fully awake after heat exhaustion, water, an oral rehydration drink or an isotonic sports drink are all reasonable. Salt tablets are not advised. Anyone who is drowsy, confused or vomiting should be given nothing by mouth until a doctor sees them.
Can heat stroke happen indoors?
Yes. Hot, humid, poorly ventilated rooms and heavy work indoors can cause it, and during a heat wave babies and older people can become dangerously overheated at home. Keeping rooms cool and checking on people who live alone matters as much as avoiding the midday sun.
How long does it take to recover?
Heat exhaustion usually settles within about thirty minutes of cooling and fluids. Heat stroke is different: recovery depends on how high the temperature went and for how long, and people often need to stay in hospital while the kidneys, muscles and brain are monitored. Sensitivity to heat can last for some weeks afterwards.