Heat-health alerts explained: what yellow, amber and red mean
What the UKHSA Heat-Health Alert colours mean, how they differ from Met Office heat warnings, and the calm, practical steps to take at each level.
By Tom Rowland · Updated 21 July 2026 · Sourced to UKHSA, the Met Office & the NHS
What a Heat-Health Alert is
When hot weather is likely to affect people's health, the UK Health Security Agency (UKHSA) issues a Heat-Health Alert through its Weather-Health Alerting system, run in partnership with the Met Office. The alerts are aimed primarily at the health and social care sector, the responder community, the voluntary and community sector and government departments, but they're public — you can register to receive them free by email — and they're a useful signal for anyone caring for someone vulnerable.
This impact-based colour system replaced the older Heatwave Plan thresholds in summer 2023, so if you remember fixed regional temperature triggers, the colours are what took their place. The core heat-alert season runs from 1 June to 30 September, though an alert can be issued outside those dates in an unusual heat episode. The service currently covers England.
What the four colours mean
The colour isn't set by a single temperature. It comes from a matrix that combines the likely impact on health with how probable that impact is. Green means no alert — minimal health impact. Yellow covers conditions unlikely to affect most people but likely to affect the particularly vulnerable, such as older adults and those with pre-existing health conditions, and is often used for shorter or less intense warm spells. Amber signals impacts likely to be felt across the whole health service, with the potential for the whole population to be at risk and non-health sectors starting to see effects. Red is the most serious: a significant risk to life even for the healthy population, with impacts spilling beyond health and social care into transport, food, water and energy.
The action each level implies is proportionate. On green or yellow it's largely business as usual — keep an eye on anyone vulnerable. Amber is the prompt to act on the practical steps below and to check on people daily. Red means treating a hot spell as you would any serious weather event: minimise time outdoors in peak heat and take the vulnerable seriously. For context, England passed 40°C for the first time on record in July 2022, so red conditions, while rare, are real.
How it differs from a Met Office heat warning
Two systems run in parallel and are easily confused. The UKHSA Heat-Health Alert is health-system facing: it describes the pressure heat is likely to put on health and social care. The Met Office extreme heat warning, part of its National Severe Weather Warning Service, is aimed at the general public and covers a broader range of impacts — travel disruption, effects on infrastructure and business, and risk to life. Both use the same yellow, amber and red colours.
At amber and red levels the two are often issued together and aligned, so you may see both at once. In plain terms: the Met Office warns you about the weather, and UKHSA translates what that weather is likely to mean for the health service. Our live tracker shows both side by side during an event.
Who is most at risk
Heat doesn't affect everyone equally. The NHS lists those most at risk as older people — especially those aged 65 and over, and anyone living alone who may be unable to care for themselves — babies and young children, people who are pregnant, and those with serious long-term conditions such as heart or breathing problems, diabetes, kidney disease or dementia. People on multiple medicines, anyone already ill and dehydrated, and those who work or exercise outdoors are also more exposed.
There's a UK-specific point worth adding: homes that overheat, particularly top-floor and single-aspect flats, can stay dangerously warm well after the outside air has cooled. If any of this describes you or someone you look out for, an amber or red alert is the cue to take the steps below seriously and to check in on each other.
Calm, practical steps for a hot spell
The official NHS and UKHSA advice is simple and mostly free. Keep out of the heat where you can, especially between 11am and 3pm; if you go out, seek shade, wear a hat and loose clothing, and take water. Close curtains and windows on the sunny side of the home during the day and open them at night when the air is cooler. Drink water regularly and go easy on alcohol, caffeine and hot drinks. Check that medicines are stored below 25°C, or as the label advises, and that the fridge and freezer are coping.
Never leave anyone — a child, an adult or a pet — in a parked car, even briefly, as temperatures inside climb fast. And the step that matters most: check on older neighbours, relatives and anyone living alone at least once a day during hot weather, because the people most at risk are often the least likely to ask for help.
Spotting heat exhaustion and heatstroke
Knowing the difference is the safety-critical part. Heat exhaustion, per the NHS, shows as tiredness, dizziness, headache, feeling sick, heavy sweating with pale, clammy skin, cramps in the arms, legs or stomach, a high temperature and intense thirst. It isn't usually an emergency if the person can cool down within 30 minutes: move them to a cool place, get them to lie down, remove any unnecessary clothing, give them water or an isotonic sports drink, and cool their skin — sponge or spray them with cool water and fan them, and put cold packs wrapped in a cloth under the armpits or on the neck.
Heatstroke is a medical emergency — call 999. Warning signs, per the NHS, are that the person is still unwell after 30 minutes of resting in a cool place, has a very high temperature, has hot skin that isn't sweating, a fast heartbeat or fast breathing, seems confused or lacks coordination, has a seizure, or loses consciousness. While you wait for help, keep cooling them and stay with them. Treat these signs the same whatever alert colour is in force — the alert level guides planning, but a person's symptoms guide your response.
Common questions
What is a Heat-Health Alert?
A warning issued by UKHSA with the Met Office when hot weather is likely to affect health. It's aimed mainly at health and social care services but is public — you can sign up to receive it free by email — and it replaced the old Heatwave Plan temperature thresholds in summer 2023.
What's the difference between a Heat-Health Alert and a Met Office heat warning?
The UKHSA Heat-Health Alert describes the pressure heat is likely to put on the health service. The Met Office extreme heat warning, part of the National Severe Weather Warning Service, is aimed at the general public and covers wider impacts like travel and infrastructure. Both use yellow, amber and red, and at higher levels are often issued together.
What does an amber heat-health alert mean I should do?
Amber means impacts are likely across the whole health service, with the whole population potentially at risk. For most households it's the cue to act on the basics — stay out of peak heat, keep the home cool, drink water — and to check on anyone vulnerable at least once a day. It's not a reason to panic, but it is a reason to take the steps seriously.
When is the heat-health alert season, and does it cover all of the UK?
The core alerting season runs from 1 June to 30 September, though an alert can be issued outside those dates during an unusual heat episode. The Weather-Health Alerting system currently covers England only.
Is a red heat-health alert an emergency?
Red is the most serious level and signals a significant risk to life even for healthy people, with impacts reaching beyond health into transport, food, water and energy. Treat it as you would any serious weather event: minimise time outdoors in peak heat and check on the vulnerable. Whatever the alert level, if someone shows signs of heatstroke, call 999.
How do I sign up for heat-health alerts?
You can register free to receive Weather-Health Alerts by email through UKHSA's guidance page on GOV.UK. The alerts are designed for the health sector and responders, but anyone can subscribe — it's a useful advance signal if you care for someone at higher risk.
Sources: GOV.UK — Weather-Health Alerting System (UKHSA guidance) · UKHSA data dashboard — Heat health alerts · Met Office — Heat-Health Alert service · NHS — Heat exhaustion and heatstroke · NHS — Heatwave: how to cope in hot weather. PreparedBritain is independent and not affiliated with HM Government.
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