Who is most at risk in a heatwave? London's heat risk explained
Older people are most at risk in a heatwave, along with babies and young children, people with heart, breathing or kidney conditions and people who live alone. In London the risk is higher because the city stays warmer at night. Here is what the official figures show, which homes overheat most, and how to keep people cool.
- heat-associated deaths, England, 2025
- 1,504
- of them in London (UKHSA)
- 317
- UKHSA's higher-risk age group
- 65 and over
- warmer in central London, hot nights
- Up to 8°C
Who is most at risk in a heatwave
Anyone can become unwell if they get too hot. The UK Health Security Agency's Beat the heat guidance (updated 21 July 2026) lists the people at higher risk of becoming seriously unwell:
- Older people aged 65 and over (the guidance used to say 75)
- Babies and young children aged 5 and under
- People with heart problems, breathing problems, dementia, diabetes, kidney disease, Parkinson's disease or mobility problems
- Pregnant women
- People on certain medicines
- People with serious mental health problems
- People who are already ill and dehydrated, for example from diarrhoea and vomiting
- People with alcohol or drug dependence
- People who are active outdoors a lot, such as runners, cyclists and walkers
- People whose jobs involve manual labour or long hours outside
- People experiencing homelessness, including those in hostels or sofa surfing
- People who live alone and may be unable to care for themselves
Heat deaths in England, summer by summer
UKHSA counts heat-associated deaths during each summer's heat episodes by comparing deaths on hot days with normal levels. These are its published estimates for England.
| Summer | Heat-associated deaths | Heat episodes | What the summer was like |
|---|---|---|---|
| 2022 | 2,985 | 5 | England's record of 40.3°C; the most heat deaths since UKHSA records began |
| 2023 | 2,295 | 5 | Eighth warmest UK summer on record |
| 2024 | 1,311 | 4 | Coolest UK summer since 2015 |
| 2025 | 1,504 | 5 | Warmest UK summer on record, mean 16.1°C |
Source: UKHSA heat mortality monitoring reports for 2022 to 2025. For 2025, UKHSA's model expected 3,039 deaths, and it says the heat alerts and the health and care response may have helped keep the real figure lower.
Who died in the heat of summer 2025
Age is the biggest factor. In 2025, UKHSA estimated 793 heat-associated deaths among people aged 85 and over, a rate of 364 per million. The rate for people aged 75 to 84 was 116 per million. UKHSA found no significant heat-associated deaths in younger age groups.
Deaths happened in care homes (677), hospitals (485) and people's own homes (326). Care homes saw the biggest rise over normal levels. Circulatory diseases, which include heart disease and strokes, were the most common underlying cause.
London had an estimated 317 heat-associated deaths over the summer, with the most during the heat of 27 June to 2 July (117) and 10 to 16 August (102).
London heatwave temperature: why the city stays hot at night
London is an urban heat island. Brick, concrete, roads and roofs soak up heat during the day and give it back after dark, and traffic and buildings add heat of their own. The Mayor's London Plan says this can make the centre of London up to eight degrees warmer than the Green Belt on hot summer nights.
On an ordinary summer night the gap is smaller. A Greater London Authority dataset for summer 2011 found midnight temperatures about 4°C higher in the city centre on average, and larger on some hot nights.
The Climate Change Committee notes that in summer, and especially in heatwaves, the heat island makes overheating worse because it stops buildings cooling down, particularly at night. Even in healthy people, it says, overheating can cause discomfort and lost sleep.
Which parts of London are most exposed
The Greater London Authority publishes Climate Risk Maps, made with Bloomberg Associates and updated in 2022 and 2024. The heat risk map combines 11 measures for small neighbourhoods across London, including air temperature, tree cover, access to green space, air pollution and the share of under-5s and over-75s, people on low incomes and people in social housing. The GLA says high climate risk goes hand in hand with income and health inequalities.
A 2024 report for the Mayor by the engineers Arup, Properties Vulnerable to Heat Impacts in London, found higher heat risk to homes towards the centre, in boroughs such as Hackney, Tower Hamlets, Islington and Camden. These boroughs have more flats, which overheat more readily than houses. Bromley, Havering and Hillingdon showed the lowest risk. The report treats top-floor flats as the most at risk, because of more sun and rising heat.
Homes that overheat most
UKHSA's keep cool at home checklist names the kinds of home that can overheat in warm weather:
- Flats on the top floor, because heat rises
- Homes with opening windows on one side only, so less air moves through
- Homes with little shade inside or out, such as no curtains, blinds or shutters
- Large east, west or south-facing windows with no shade from the sun
- Homes in densely built-up areas with little green space nearby
- Some highly insulated or energy-efficient homes, which can trap heat inside
- Homes with appliances or hot water systems that give off a lot of heat
- Homes where windows only open a little, for example because of a safety catch
Heat-Health Alerts: what the colours mean
UKHSA runs Heat-Health Alerts for England with the Met Office. Since 2023 they have been based on the likely impact on health, with colours that match Met Office weather warnings. The main season runs from 1 June to 30 September.
| Alert | What UKHSA says it means |
|---|---|
| Green | No alert |
| Yellow | Heat unlikely to affect most people, but it could affect those who are particularly vulnerable |
| Amber | Impacts likely to be felt across the whole health service |
| Red | Significant risk to life, even for healthy people |
You can sign up to get the alerts by email from UKHSA's Heat-Health Alerting page on gov.uk.
How to protect someone at risk
Check on them
Call or visit family, friends and neighbours who may be at higher risk, especially anyone who lives alone, and see if they need help. UKHSA asks everyone to do this in hot weather.
Keep the sun out by day
Close curtains and blinds on windows in direct sun during the day. Open windows when the air outside feels cooler, for example at night, if it's safe to do so.
Use the coolest room
Move to the coolest part of the home, especially for sleeping. The NHS suggests checking the temperature of rooms where people at higher risk live and sleep.
Use fans the right way
UKHSA says electric fans help when the air temperature is below 35°C. Don't aim a fan straight at the body, as that can lead to dehydration. Check the heating is off.
Drink and stay out of the midday sun
Drink plenty of fluids. If going out, stay in the shade, especially between 11am and 3pm, as the NHS advises.
Know when to get help
If you're worried about symptoms or they're getting worse, contact NHS 111. In an emergency, or if you think someone has heatstroke, call 999.
Where cooling fits
The official advice starts with shade, ventilation and moving to a cooler room. That works in many homes. It's harder in a top-floor or single-aspect flat that stays hot all night, or for someone who can't easily move between rooms.
A room that stays cool gives someone at risk a reliable place to rest and sleep through a heatwave. A modern wall unit cools one room quietly, and the same unit heats that room in winter. Our guides on keeping a bedroom cool and on whether air conditioning is worth it cover the choices in more detail.
Heatwave risk questions
Who is most at risk in a heatwave?
UKHSA lists older people aged 65 and over, babies and children aged 5 and under, people with heart, breathing or kidney conditions, dementia, diabetes or Parkinson's disease, pregnant women, people on certain medicines, people who live alone and people who work or exercise outside. The 2025 figures show deaths are concentrated among people aged 75 and over.
Why is London hotter than the rest of the UK in a heatwave?
London is a large urban heat island. Buildings and roads store heat by day and release it at night, so the city cools down less. The London Plan says central London can be up to eight degrees warmer than the Green Belt on hot summer nights.
How many people died in the 2025 heatwaves in England?
UKHSA estimates 1,504 heat-associated deaths in England across five heat episodes in summer 2025, including 317 in London. That compares with 1,311 in 2024, 2,295 in 2023 and 2,985 in 2022.
What temperature is dangerous for older people indoors?
UKHSA and the NHS don't give one indoor temperature that is safe for everyone. Their advice is to keep the home as cool as possible, check the temperature of rooms where at-risk people live and sleep, and get advice from NHS 111 if someone is unwell.
What does an amber heat-health alert mean?
UKHSA says an amber alert means the heat is likely to affect the whole health service, and a coordinated response may be needed. A red alert means a significant risk to life even for healthy people. Alerts cover England and run mainly from 1 June to 30 September.
Are top-floor flats more dangerous in a heatwave?
They are more likely to overheat. UKHSA's checklist names top-floor flats and homes with windows on one side only, and a 2024 report for the Mayor of London treats top-floor flats as the most at-risk homes because of more sun and rising heat.
Do fans help in a heatwave?
UKHSA says electric fans can help when the air temperature is below 35°C. Don't point a fan straight at your body, as it can lead to dehydration. Above 35°C, focus on keeping the room cool and drinking enough.