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Heat is the leading cause of weather-related deaths, according to the World Health Organization (WHO). It can worsen underlying health conditions, including heart disease, diabetes, asthma, and mental health, and increase the risk of accidents.
New research by University College London (UCL) and the London School of Hygiene & Tropical Medicine has found that the annual number of heat-related deaths in England and Wales is set to rise up to fifty-fold over the next 50 years, largely due to climate change and an ageing population.
A heatwave can cause dehydration, headaches, lethargy and overheating, as well as heat exhaustion and heatstroke, which are potentially serious conditions. So, it’s not surprising that the Government is warning healthcare professionals and the public to be prepared for the health impacts of heat whenever temperatures climb higher than usual.
In late June 2025, NHS website visits to heat exhaustion and heatstroke advice surged by nearly 200 per cent following a Heat Health Alert (HHA), according to an analysis by NHS England (NHSE).
“People with respiratory, cardiovascular or other underlying health conditions, babies, small children and other vulnerable groups are particularly at risk,” says Dr Jess Neumann, associate professor in hydrology at the University of Reading. “But none of us are immune, and we must look after ourselves to stay safe and well.
Don’t underestimate the heat. Drink plenty of fluids, stay out of the direct sun, seek shade and cooler areas, avoid exercising, apply suncream if in the sun and wear appropriate clothing.”
Heat mortality monitoring
The UK Health Security Agency (UKHSA) publishes an annual report on heat mortality to understand how heat affects health. The report estimates how many extra deaths occurred during periods of hot weather, known as heat-associated deaths.
Experts then compare the number of deaths during heatwaves with the number that occurred on other summertime days. Since summer 2024 was one of the coolest in recent years, the UKHSA’s Heat mortality monitoring report, England: 2024 published in April 2025, gives important insights into how even moderately high temperatures can influence mortality during the summer months.
According to the report, there were 1,311 heat-associated deaths in England during the four heat episodes in the summer of 2024. This was 282 more deaths than predicted. The highest heat-associated mortality rates were seen in people aged 85 and over, followed by those aged 75-84.
More deaths occurred earlier in the summer than in the later heat episodes. The South East had the highest number of heat-associated deaths over the summer, but significant heat-associated mortality was also seen in other areas of England.
There was significant heat-associated mortality across the summer for those who died in care homes, in hospitals and at their own home. There was no significant heat-associated mortality for those who died in hospices or in other places.
Anyone can be vulnerable to the health effects from the heat, but people at the highest risk include those over 65, babies and children, pregnant women, people with a chronic or underlying health problem, and those on low income.
This year, for the first time, the UKHSA’s Heat Mortality Monitoring Report has analysed heat-associated mortality according to the underlying cause of death. In summer 2024, the leading cause for heat-associated mortality was ‘All circulatory diseases’ followed by ‘Dementia and Alzheimer’s’.
This isn’t too surprising, as cardiovascular diseases and neurological diseases are the highest risk factors for heat-associated mortality. Heat-associated deaths were also significantly associated with flu and pneumonia, but these weren’t significant for cancer, chronic lower respiratory diseases, or external causes.
Heat-Health Alert
The UKHSA and the Met Office have co-developed the Heat-Health Alert (HHA) system to help people stay safe when temperatures rise. This system provides early warning information to the public, the NHS, local authorities and emergency responders about heat-related health risks that may occur during hot weather. Alerts are colour-coded (yellow, amber or red) to reflect the level of impact expected.
A yellow alert means that hot weather is expected to impact vulnerable individuals, potentially leading to increased healthcare service usage. An amber alert means that weather impacts are likely to affect the wider population too and may be felt across the whole health service. A red alert means a significant risk to life.
The summer of 2024 was the coolest summer for the UK since 2015. Only four heat episodes occurred, and no amber or red HHAs were issued in any region of England.
According to the Heat mortality monitoring report, England: 2024, significant heat-associated deaths were seen in three out of the four heat episodes of the summer, despite only yellow HHAs being issued. This included short spells of heat lasting only three days.
These findings show that even moderate heat can result in serious health outcomes and mortality, especially for older adults, babies and young children, and those with certain pre-existing health conditions.
“Findings show that even moderate heat can result in serious health outcomes and mortality”
People with respiratory, cardiovascular or other underlying health conditions, babies, and small children are particularly vulnerable to heat exhaustion and heatstroke when temperatures increase.
Managing health risks
The body naturally cools down through sweating and increased blood flow to the skin. Anything that reduces sweating can cause the body to overheat.
Heat exhaustion is mainly caused by dehydration. Signs include tiredness, dizziness, headaches, feeling sick, sweating, pale and clammy skin, muscle cramps (stomach and limbs), fast breathing, fast heartbeat, a fever, feeling very thirsty and feeling weak. This doesn’t usually need emergency medical help as long as the affected person cools down within 30 minutes.
The NHS advises moving them to a cool place, removing unnecessary clothing, giving them a rehydration drink or cool water, and cooling their skin. Their breathing, pulse and responsiveness should be monitored.
If heat exhaustion isn’t treated quickly, it can lead to heatstroke, which causes a very high internal body temperature (40˚C and above) and a decreased level of consciousness. An affected person could become confused, unresponsive or even aggressive. If someone has signs of heatstroke, it’s important to call 999 immediately.
Research by St John Ambulance in June 2025 revealed that 55 per cent of adults surveyed in England don’t know the difference between heatstroke and heat exhaustion, with almost one in 10 adults believing that heat exhaustion isn’t serious.
There are also widespread misconceptions about how to treat heatstroke. Many survey respondents believed that giving a patient water to drink was the correct next step after calling emergency services, when in fact cooling them down using water on their skin and fanning is more effective.
The research also found that four in 10 people are unaware that some medicines for common long-term conditions, including certain antidepressants, diuretics and beta blockers, can increase the risk of heat-related illness.
“Older people, while more confident in managing their health in the sun, were less aware of the risks posed by certain medications,” says Lydia Scroggs, head of clinical strategy and policy at St John Ambulance.
“This is most concerning, given that both older adults and young children are more vulnerable to heat-related illnesses, so extra precautions are essential.”
UK’s Adverse Weather and Health Plan
The Adverse Weather and Health Plan (AWHP) 2025 to 2026, published by the UK Health Security Agency (UKHSA) in March 2025, is a structured document that aims to protect individuals and communities from the health effects of different types of weather (such as heat, cold, flooding, drought, etc.) and to build community resilience. The goal of the AWHP is to:
- Stop people losing their lives in adverse weather
- Reduce the higher risk of death due to adverse weather conditions
- Stop people getting ill or injured in adverse weather
- Reduce the need to use healthcare services due to the adverse weather.
The report outlines how the UKHSA, Government, local authorities and voluntary groups should be working together nationally, regionally and locally. It also focuses on improving research into weather-related health issues and communicating the risks to everyone affected.
A key aspect of the AWHP is a series of guidance documents for both health and social care staff and the public so that they are prepared in advance for extreme weather (e.g. cold or heat) and know how to stay safe and healthy once the adverse weather arrives. Free online training materials and information are available.
The Heat-Health Alerts and Cold-Health Alerts are issued in various ways, including via the news, social media, the UKHSA, Met Office, government departments and agencies, NHS England and local authorities.
The AWHP and Weather Health Alert System user guide is available in easy-to-read versions, while the ‘Beat the heat’ guidance has been translated into the 11 most commonly spoken languages in Britain. British Sign Language (BSL) versions have also been produced.
Details of the UKHSA’s Weather Health Alerts can be found here: ukhsa-dashboard.data.gov.uk/weather-health-alerts.
Support from the pharmacy
According to the UKHSA, checking in on vulnerable people at a higher risk of heat-related illness is important. Pharmacy teams are well-placed to give customers advice on staying cool and keeping well in a heatwave.
They should therefore stay informed about official heat warnings by checking for local weather warnings and signing up for the UKHSA Heat Health Alert (see above).
Advice to pass on to customers includes:
- Make sure you have enough of your regular medicines and know how to store them in hot temperatures
- Stock up on items such as sunscreen, aftersun and rehydration tablets
- Avoid going outside and doing strenuous activity during the hottest part of the day
- Drink one cup of water per hour and at least two to three litres per day – don’t wait to drink until you’re thirsty, and always carry water with you when you’re out and about
- Avoid drinking alcohol or caffeinated drinks as these can act as diuretics
- Wear light-coloured, loose clothing and stay in the shade as much as possible
- Keep homes cool by closing curtains and windows if it’s hotter outside than inside and turn off as many electrical devices as possible
- Use electric fans only when temperatures are below 40˚C/104˚F – when temperatures rise above 40˚C/104˚F, fans will heat your body
- Wet your skin and hair (and even light clothing) before bedtime – with a lukewarm or cool shower or bath, damp cloth or spray
- Sleep with a thin, cotton sheet as this will absorb sweat.
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