How to Stay Well During a London Heatwave and When to Seek Help
By Dr Daniel Gordon • 24, Jun 2026
Hot weather can be enjoyable: longer days, brighter evenings and more time outdoors can lift our mood and help us feel more active.
During a heatwave, however, the body has to work much harder to keep itself cool. When temperatures stay high for several days, especially in busy cities such as London, the risk of dehydration, heat exhaustion and heatstroke increases.
Some people are more vulnerable than others, including older adults, babies, young children, pregnant women, people with long-term health conditions and those taking certain medications.
This article explains how heat affects the body, how to stay hydrated, how to keep yourself and your home cool, and when symptoms need medical attention.
Why Heatwaves Can Affect Your Health
The human body is constantly trying to maintain a stable internal temperature.
When we get too hot, we cool ourselves mainly through sweating and by increasing blood flow to the skin. That is why we may look flushed, feel sweaty, or notice our heart beating faster in hot weather.
The problem is that these cooling mechanisms have limits.
If the air is very hot, if humidity is high, or if we are not drinking enough, the body can struggle to lose heat effectively. Over time, this can lead to dehydration, heat exhaustion and, in more serious cases, heatstroke.
Heat can also make existing health problems worse. People with heart disease, breathing conditions, kidney problems, diabetes or frailty may be more vulnerable because their bodies have less reserve to cope with the extra stress.
This is particularly important in cities such as London, where dense buildings, traffic, concrete surfaces and limited airflow can make hot weather feel even more intense. The city can hold onto heat, especially later in the day, and indoor spaces can become difficult to cool once they have overheated.
Hydration During a Heatwave: What Actually Helps
Hydration is one of the simplest and most important parts of staying well during a heatwave.
When we sweat, we lose fluid. If that fluid is not replaced, dehydration can develop.
Early signs of dehydration can include:
thirst
headache
tiredness
dizziness
dry mouth
darker urine
passing urine less often
A useful general rule is to drink regularly throughout the day, rather than waiting until you feel very thirsty.
Water is usually best. Diluted squash, milk and oral rehydration drinks can also be useful in some situations. If you are going out, take a refillable bottle of water with you, especially if you are travelling on public transport.
Alcohol is best avoided or kept low during very hot weather because it can worsen dehydration and impair judgement. Caffeinated drinks are not automatically forbidden, but relying heavily on coffee, strong tea or energy drinks is not ideal in a heatwave. The priority should be regular fluids that genuinely rehydrate you.
Older adults can be at particular risk because the sensation of thirst may become less reliable with age. Children may also need reminding to drink, especially when they are busy playing.
How to Keep Cool During the Day
Keeping cool is not only about drinking more water.
It is also about reducing the amount of heat your body has to deal with.
During a heatwave, try to stay out of direct sun during the hottest part of the day, usually between 11am and 3pm. If you do need to go outside, seek shade, wear loose light clothing, use high-factor sunscreen, wear sunglasses and consider a wide-brimmed hat.
Strenuous activity is best moved to the cooler parts of the day, such as early morning or later evening. This applies to exercise, gardening, walking long distances and physical work.
If you start to feel dizzy, faint, unusually tired, sick or confused, stop what you are doing. These are not signs to push through.
Heatwave Advice for London: Travel, Parks and Open Water
For people living or working in London, heatwaves can create some specific challenges.
The Underground can become particularly hot, especially on deeper lines and during busy travel times. If you need to use the Tube during a heatwave, carry water with you, avoid rushing, and give yourself extra time. If you begin to feel faint, dizzy, sick or unusually weak, get off at the next safe opportunity and cool down.
London’s parks and green spaces can offer shade and a welcome break from heat trapped by buildings and roads. Places such as Hyde Park, Regent’s Park, Hampstead Heath and local green spaces can feel more comfortable than busy streets during hot weather. Even so, shade is not complete protection, so sun protection and regular fluids still matter.
One important warning is open water.
During very hot weather, rivers, lakes, reservoirs and canals can look tempting. But open water can be dangerous, even when the air feels warm. Cold shock, hidden currents, sudden changes in depth, weeds and poor water quality can all create serious risks.
The River Thames, in particular, should not be treated as a safe place to cool off. If you want to swim, use a properly supervised swimming area or pool.
How to Keep Your Home Cool in a Heatwave
Homes can become very hot during a heatwave, particularly flats, top-floor rooms and homes with windows that receive direct sun.
The key is to keep heat out during the day and let cooler air in when the temperature drops.
Close curtains or blinds on sun-facing windows during the day. In many homes, it is better to keep windows closed during the hottest part of the day if the air outside is warmer than the air inside. Then open windows later in the evening, overnight or early in the morning when the air outside is cooler, if it is safe to do so.
A fan can help some people feel more comfortable, especially when used with good airflow. Placing a bowl of ice or a frozen water bottle in front of a fan may create a cooler breeze, although it is not a substitute for keeping the home itself as cool as possible.
Night-time heat can be particularly difficult. A cool or lukewarm shower before bed, light cotton bedding, and sleeping in the coolest room in the home may help. If bedrooms are very hot, it may be worth temporarily sleeping in a cooler room.
If your home is uncomfortably hot, spending a few hours somewhere cooler — such as a library, community space, shopping centre or shaded public building — can make a real difference.
Medication and Hot Weather
Some medicines can be affected by heat, and some can also affect how the body manages temperature, hydration or sweating.
Many medicines should be stored in a cool, dry place away from direct sunlight. Some need to be kept below a certain temperature, and a small number require refrigeration.
Do not put medicines in the fridge unless the packaging says to do so or a pharmacist has advised it. But if your home is becoming very hot, or you are worried about a particular medicine, ask your pharmacist for advice.
It is also important not to stop prescribed medication because of hot weather without speaking to a healthcare professional. Some people may need extra monitoring or advice during a heatwave, particularly if they take diuretics, blood pressure medication, heart medication, or medicines that affect the nervous system.
Heat Exhaustion: Symptoms to Recognise
Heat exhaustion happens when the body is overheating and struggling to regulate itself.
It can affect adults and children, and it may come on gradually.
Common symptoms include:
headache
dizziness
tiredness or weakness
feeling sick or being sick
heavy sweating
pale, clammy skin
muscle cramps
intense thirst
a high temperature
fast breathing or a fast pulse
irritability or confusion
If someone appears to have heat exhaustion, the first step is to cool them down.
Move them to a cooler place. Remove unnecessary clothing. Encourage them to drink cool fluids if they are able to. Cool the skin with water, a fan, damp cloths or cool packs wrapped in a towel.
Many people improve if they are cooled down promptly.
But if symptoms are not improving, or the person is becoming more confused, drowsy or unwell, this needs urgent medical attention.
Heatstroke: When Heat Becomes an Emergency
Heatstroke is different from heat exhaustion.
Heat exhaustion is serious, but it can often improve with cooling and fluids. Heatstroke is a medical emergency.
It happens when the body can no longer control its temperature properly. The internal temperature rises dangerously, and organs can be affected.
You should seek urgent help if someone has:
confusion
loss of consciousness
a seizure
collapse
very hot skin
rapid breathing
symptoms that do not improve after cooling
severe weakness or unusual drowsiness
Do not wait to see if it passes.
While waiting for help, move the person somewhere cool and continue trying to lower their temperature.
Who Is Most at Risk During a Heatwave?
Heat can affect anyone, but some people are more vulnerable.
This includes:
older adults, especially those living alone
babies and young children
pregnant women
people with heart, lung or kidney conditions
people with diabetes
people with serious mental health conditions
people who are homeless or living in poorly ventilated accommodation
people who live in top-floor flats or very hot homes
people who work outdoors
people taking medications that affect hydration, sweating or temperature regulation
This is why checking on vulnerable relatives, neighbours or friends matters. A quick phone call or visit can make a real difference, especially for someone who may not realise how hot their home has become or may struggle to get fluids.
Exercise During a Heatwave
Exercise is good for health, but timing matters during very hot weather.
Strenuous activity during the hottest part of the day can increase the risk of dehydration and heat illness. This is especially true for running, cycling, outdoor sports and heavy physical work.
If you want to stay active during a heatwave, aim for early morning or later evening when temperatures are lower. Reduce the intensity, take breaks, and drink regularly.
Children should not be pushed into strenuous physical activity on very hot days. This applies to sports clubs, long walks, playgrounds in direct sun and extended time outdoors without shade.
If you feel dizzy, faint, unusually breathless, sick or confused, stop. These are not signs to push through.
When to Seek Medical Help
You should seek medical advice if you or someone you are caring for has symptoms of dehydration or heat exhaustion that are not improving with cooling and fluids.
You should be more cautious with babies, young children, older adults, pregnant women, and people with long-term health conditions.
Urgent help is needed if someone is confused, very drowsy, has collapsed, has a seizure, has severe weakness, or does not improve after being moved somewhere cool.
The important message is this: heat-related illness can escalate quickly, but it is often preventable.
Drink regularly. Keep cool. Avoid the strongest sun. Be careful when travelling. Keep your home as cool as possible. Avoid risky open water. Check on vulnerable people.
Hot weather can be enjoyed. But during a heatwave, the body deserves a little more respect.
Disclaimer
This blog post provides general information only. It is not intended to provide instruction and you should not rely on this information to determine a diagnosis, prognosis or course of treatment. It should not be used in place of a professional consultation with a doctor.
The medical information is the personal opinion of the stated author(s). It is based on available evidence or, where no published evidence is available, on current medical opinion and practice.
Every effort is taken to ensure that the information contained in this website is accurate and complete. However, accuracy cannot be guaranteed – rapid advances in medicine may cause information contained here to become outdated, invalid or subject to debate.
The author(s) is/are not responsible for the results of your decisions resulting from the use of the information, including, but not limited to, your choosing to seek or not to seek professional medical care, or from choosing or not choosing specific treatment based on the information.
You should not disregard the advice of your physician or other qualified healthcare provider because of any information you read on this website. If you have any health care questions, please consult a relevant medical practitioner.
