How do heat and cold-health alerts work?
Getty ImagesA yellow heat-health alert has been issued, with temperatures predicted to hit 32C (86F) on Tuesday.
All areas of England, except the North East and North West, are covered by the warning, until Wednesday.
How does the weather health alert system work?
The weather alert service warns the public when high or low temperatures could damage their health.
Run by the UK Health Security Agency (UKHSA) and the Met Office, the system, for England, was introduced in June 2023.
It includes both heat-health alerts and cold-health alerts.
Heat-health alerts are typically issued between 1 June and 30 September, and cold-health alerts between 1 November and 30 March.
The system issues warnings to members of the public, and sends guidance directly to NHS England, the government and other healthcare professionals during periods of adverse weather.
Alerts are categorised according to severity and include:
- headline weather conditions expected in the coming days
- details of how weather conditions will affect each region
- links to additional information, advice and guidance
The system was designed to help reduce illness and deaths by improving communication between the public and relevant bodies during periods of extreme weather.
What does each level mean?
The level of alert is based on Met Office forecasts and data.
There are four levels ranging from green (least severe) to red (most severe):
Green
Green is the normal level, when advice is given on how people should prepare to respond if temperatures rise or fall.
Yellow
Yellow alerts are issued during periods of hot or cold weather that are only likely to affect those who are particularly vulnerable, for example the elderly, or those with existing health conditions.
Amber
Amber alerts are issued in situations that could potentially put the whole population at risk. The NHS may see increased demand on GPs and ambulances, for example.
Travel disruption is also likely.
Red
A red alert is the most severe.
It is issued in situations when hot or cold weather would be a significant risk to life, for even the healthy population, and could lead to failures of critical national infrastructure, such as power outages or roads and rail lines being closed.
What does hot weather do to the body?
As the body gets hotter, blood vessels open up. This leads to lower blood pressure and makes the heart work harder to push the blood around the body.
This can cause mild symptoms such as an itchy heat rash or swollen feet as blood vessels become leaky.
At the same time, sweating leads to the loss of fluids and salt and, crucially, the balance between them in the body changes.
This, combined with the lowered blood pressure, can lead to heat exhaustion and heatstroke. Symptoms include:
- dizziness
- nausea
- fainting
- confusion
- muscle cramps
- headaches
- heavy sweating
- tiredness
If blood pressure drops too far, the risk of heart attacks rises.