Heat exhaustion and heatstroke often seem to appear suddenly, but in many cases the warning signs begin earlier: feeling unusually tired, thirsty, dizzy, headachey, sweaty or weak. By the time someone faints, becomes confused or stops coping with the heat, the body may already be under significant strain.
That is why prevention matters. During hot weather, the aim is not just to treat symptoms once they appear. It is to avoid getting to that point in the first place.
This guide explains how to reduce your risk of heat exhaustion and heatstroke, how to keep yourself and your home cooler, who is most at risk, and what early symptoms should make you stop, cool down and seek help if needed.
Key message: Heat illness is easier to prevent than treat. Drink regularly, avoid the hottest part of the day, keep your living space cool, slow down physical activity, and act early if you feel dizzy, weak, sick, headachey or confused.
Why heat exhaustion happens
Your body is constantly trying to keep its temperature within a safe range. When it is hot, you cool down mainly by sweating and sending more blood flow to the skin. This works well up to a point, but it puts extra demand on the body.
If you are losing fluid through sweat, not drinking enough, exercising, working outdoors, sitting in a hot room, travelling on hot public transport, drinking alcohol, or already unwell, the body can start to struggle. This can lead to dehydration and heat exhaustion.
Heat exhaustion is the warning stage. It can cause symptoms such as headache, dizziness, heavy sweating, tiredness, thirst, nausea, cramps and a fast pulse. If the body cannot cool down, heat exhaustion can progress to heatstroke, which is a medical emergency.
If you want a symptom-by-symptom guide, read our article on heat exhaustion and heatstroke. If dizziness is one of your main symptoms, our guide to dizziness and when to worry may also be helpful.
The best way to prevent heat illness: act before you feel ill
One of the biggest mistakes people make in hot weather is waiting until they feel unwell before changing what they are doing. By then, dehydration, overheating or low blood pressure may already be developing.
Prevention means planning your day around the heat. That might mean walking the dog earlier, exercising in the morning, closing curtains before rooms heat up, carrying water when travelling, or checking on an older relative before symptoms appear.
NHS advice on heat exhaustion and heatstroke includes drinking more cold drinks, wearing light-coloured loose clothing, avoiding the sun between 11am and 3pm, avoiding excess alcohol and avoiding extreme exercise during hot weather.
Keep out of the strongest heat
In the UK, people often underestimate hot weather because it may not last long. But short periods of intense heat can still be dangerous, especially when homes, workplaces and transport are not designed for it.
The hottest part of the day is usually late morning to mid-afternoon. If possible, avoid being outside in direct sun between 11am and 3pm. This is especially important for babies, young children, older adults, pregnant women, people with long-term conditions, and anyone doing physical activity.
If you need to go out, use shade wherever possible. Walk on the shaded side of the street, take breaks indoors, avoid unnecessary rushing, and plan errands for early morning or evening. A short walk that feels easy on a mild day can become much harder during a heatwave.
Drink before you are very thirsty
Thirst is useful, but it is not always an early enough warning sign. Some people, especially older adults, may not feel thirsty even when they are becoming dehydrated. Children may also forget to drink when they are playing.
Try to drink regularly throughout the day. Water is usually the best choice. You can also get fluid from milk, diluted squash, fruit, salads, soups and other foods. If you are sweating heavily, have diarrhoea or vomiting, or are struggling to rehydrate, a pharmacist may advise oral rehydration salts.
Watch for signs that you are not drinking enough:
- dark yellow or strong-smelling urine
- peeing less often than usual
- dry mouth or lips
- headache
- dizziness when standing
- feeling weak, tired or foggy
For more detail, read our guide to dehydration symptoms in adults and children.
Be careful with alcohol and caffeine
Alcohol can make heat illness more likely. It may increase fluid loss, disturb sleep, affect judgement and make it easier to miss early warning signs. A few drinks in the sun can quickly become a problem if you are also sweating, not eating properly or spending hours outdoors.
Caffeine is not automatically dangerous, but large amounts of coffee, energy drinks or cola can make some people feel jittery, worsen sleep or replace water during the day. During hot weather, it is sensible to drink water regularly as well.
If you are at a barbecue, festival, pub garden, beach, park or outdoor event, alternate alcoholic drinks with water and take breaks from the sun.
Wear clothing that helps your body cool down
Clothing can make a big difference. Loose, light-coloured clothing helps air move around the skin and reflects more sunlight than dark, tight clothing. Natural or breathable fabrics can feel cooler than heavy synthetic materials.
A wide-brimmed hat can help protect your face, scalp and neck. Sunglasses can protect your eyes. Sunscreen is important for preventing sunburn, but it does not stop your body overheating, so it should be combined with shade, fluids and sensible activity levels.
Sunburn can make it harder for your body to regulate temperature and may happen even when it does not feel extremely hot. For more on this, read our guide to sunburn and sun safety.
Keep your home cooler
Many UK homes become uncomfortable during heatwaves, particularly flats, top-floor rooms, poorly ventilated spaces and homes with large windows facing the sun. Heat can also build up over several days, so a home may become hotter indoors than outdoors.
To keep your home cooler:
- close curtains or blinds in rooms facing the sun
- open windows when the air outside is cooler than inside
- close windows if the air outside is hotter than your home
- turn off lights and electrical devices that give off heat
- move to the coolest room if possible
- use a fan if it helps you feel cooler
- take a cool shower or put cool water on your skin or clothes
- avoid using the oven during the hottest part of the day if you can
UKHSA’s Beat the Heat guidance explains that anyone can become unwell if they get too hot, and gives practical advice on cooling yourself and your home.
Slow down exercise and physical work
Exercise and physical work are common triggers for heat exhaustion. This includes running, cycling, football, gym sessions, gardening, DIY, construction work, delivery work and long walks.
Your usual pace may not be safe in high heat. Even fit people can develop heat illness if they push too hard, especially when humidity is high or they are not used to the temperature.
During hot weather:
- exercise early in the morning or later in the evening
- reduce intensity and duration
- take more breaks than usual
- drink before, during and after activity
- avoid “pushing through” dizziness, nausea, cramps or weakness
- stop immediately if you feel faint, confused or unusually unwell
If you develop dizziness, faintness or blackouts during or after heat exposure, take it seriously. Our guides to dizziness and fainting and blackouts explain when symptoms may need urgent help.
Plan travel carefully
Cars, buses, trains and stations can become very hot. Delays, crowded carriages and long walks between stops can make overheating more likely. Always carry water if you are travelling during hot weather, even for short journeys.
Never leave babies, children, older people, vulnerable adults or pets in a parked car, even briefly. Temperatures inside vehicles can rise quickly and become dangerous.
If you are travelling with children, plan extra drink breaks, shade breaks and lighter clothing. For older relatives or people with mobility problems, consider whether the journey can be moved to a cooler time of day.
Check on people who are more vulnerable
Heat illness can affect anyone, but some people are at higher risk of becoming seriously unwell. This includes:
- babies and young children
- older adults, especially those living alone
- people with heart, lung, kidney or diabetes-related conditions
- people with dementia or severe mental health conditions
- people with mobility problems or disabilities
- pregnant women
- people taking certain medicines, including some water tablets and blood pressure medicines
- people who work outdoors
- people who are homeless or living in housing that becomes very hot
Checking in can be simple: ask whether they have enough to drink, whether their home feels too hot, whether they have opened or closed windows at the right times, and whether they are feeling dizzy, weak, sick, confused or unusually tired.
Older people may not complain until symptoms are advanced. A quick visit or phone call during a heatwave can make a real difference.
Heat prevention for babies and children
Children can overheat quickly because they are active, may not drink enough, and may not recognise early symptoms. Babies are especially vulnerable because they cannot tell you they are too hot or thirsty.
To reduce risk:
- keep babies and young children out of direct sun as much as possible
- offer drinks regularly
- continue breast or bottle feeds as advised
- dress children in light, loose clothing
- use shade, hats and sunscreen where appropriate
- avoid energetic outdoor play during the hottest part of the day
- check babies are having wet nappies as usual
- never cover a pram with a blanket that blocks airflow
A tired, floppy, unusually sleepy, confused, very hot or poorly responsive child needs urgent medical advice. If a child has very few wet nappies, no tears when crying, dry mouth, sunken eyes or seems very unwell, dehydration may be a concern.
Heat prevention at work
Some jobs make heat exposure harder to avoid. Outdoor workers, delivery drivers, kitchen staff, care workers, warehouse workers and people in uniforms or protective equipment may be at higher risk.
Practical steps include regular breaks, access to drinking water, shaded or cooler rest areas, adjusted workloads, earlier start times, and avoiding the most physically demanding tasks during the hottest part of the day where possible.
If you are an employer or manager, heat should be treated as a health and safety issue, not just discomfort. Staff may need flexibility, especially those who are pregnant, have health conditions, take certain medicines or are doing strenuous work.
Know the early warning signs
Preventing heatstroke means acting when heat exhaustion may be starting. Do not wait until someone collapses.
Stop what you are doing and cool down if you or someone else develops:
- dizziness or lightheadedness
- headache
- unusual tiredness or weakness
- feeling sick
- muscle cramps
- heavy sweating
- intense thirst
- fast breathing or fast pulse
- feeling faint
Move somewhere cooler, loosen clothing, drink fluids if able, and cool the skin with water, a fan, damp cloths or a cool shower. If symptoms do not improve after cooling down, seek medical advice.
Do not ignore early symptoms: Dizziness, nausea, cramps, weakness and feeling faint in hot weather are signs to stop, cool down and rehydrate. Continuing activity can make heat illness worse.
When prevention has not been enough: what to do
If someone looks like they may have heat exhaustion, act immediately:
- Move them to a cooler place.
- Help them lie down or sit with support.
- Remove unnecessary clothing.
- Give cool drinks if they are awake and able to swallow.
- Cool their skin with water, a fan, cool cloths or wrapped cold packs.
- Stay with them and monitor their symptoms.
They should start to feel better within about 30 minutes. If they do not improve, or symptoms are severe, get urgent medical help.
When to call 999
Call 999 if you think someone has heatstroke. This is an emergency.
Warning signs include:
- confusion or unusual behaviour
- collapse or loss of consciousness
- a seizure or fit
- very hot skin
- not sweating despite being very hot
- severe breathlessness
- chest pain
- symptoms that do not improve after 30 minutes of cooling
While waiting for help, keep cooling the person. Do not give them anything to drink if they are unconscious, very drowsy or unable to swallow safely.
A simple hot-weather checklist
Before a very hot day, ask yourself:
- Do I have enough water at home and when travelling?
- Can I move exercise, errands or outdoor work to a cooler time?
- Have I closed curtains or blinds in sunny rooms?
- Do I know which room is coolest?
- Have I checked on older relatives, neighbours or vulnerable people?
- Are children drinking and resting enough?
- Am I avoiding too much alcohol in the heat?
- Do I know the early signs of heat exhaustion?
This kind of preparation can stop a hot day becoming a health emergency.
Final thoughts
Heat exhaustion and heatstroke are not just problems for holidays abroad. They can happen in the UK during heatwaves, hot workplaces, warm homes, outdoor events, sport, gardening and travel.
The best protection is early action: drink regularly, avoid the strongest sun, keep your home cooler, slow down physical activity, wear suitable clothing and check on people who may be more vulnerable.
If you start to feel dizzy, weak, sick, headachey or faint in hot weather, stop and cool down. If someone becomes confused, collapses, has a seizure, has chest pain or does not improve after cooling, call 999.
For official advice, see NHS guidance on how to cope in hot weather, NHS guidance on heat exhaustion and heatstroke, and UKHSA’s Beat the Heat guidance.
This article is for general information only and should not replace medical advice. If you are worried about your symptoms or someone else’s, contact NHS 111, your GP, or call 999 in an emergency.
