During the summer, many of us enjoy the longer days, warmer evenings, and time outdoors. But warmer weather also brings potential risks to health, especially when temperatures climb higher than usual.
This year, the Met Office 3-month outlook suggests that the likelihood of a warm summer in the UK is higher than that of a typical season, so we need to be prepared for the health impacts of heat. But how exactly does heat impact the body, and what can we do to avoid the negative effects?
Heat affects everyone
Most health impacts seen during heat events in England are from diseases associated with the heart, blood vessels and lungs. Our bodies naturally cool down through sweating and by increasing blood flow to the skin.
When the temperature outside the body is higher than the temperature of the skin, the only effective way to lose heat is through sweating. So, anything that reduces sweating can cause the body to overheat. This can happen due to:
- dehydration
- lack of breeze
- tight-fitting clothes
- certain medications
- conditions that affect the body’s ability to sweat
The choices we make during hot weather can also make a big difference to how hot we become: simple actions like using fans, wearing loose clothing, or drawing curtains to keep rooms cool, can help to keep temperatures at safer levels.
High temperatures can affect anyone, not just those traditionally seen as vulnerable. Heat exhaustion and heatstroke are serious and potentially life-threatening conditions, so it’s worth knowing the signs to look out for and how to respond.
The role of Heat-Health Alerts
UKHSA and the Met Office co-developed the Heat-Health Alert (HHA) system, as part of our efforts to help people stay safe when temperatures rise.
The HHA 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. This allows people to take the right steps to protect themselves and others.
To understand how heat affects health, UKHSA publishes an annual report on heat mortality, which is now badged as Official Statistics.
These reports estimate how many extra deaths occurred during periods of hot weather, known as heat-associated deaths. This is done by comparing the number of deaths during heatwaves with the number that occurred on other summertime days. While summer 2024 was one of the coolest in recent years, our latest annual heat mortality report gives important insights into how even moderately high temperatures can influence mortality during summer.
The report also compares the number of heat-associated deaths in 2024 with what we would have predicted for 2024’s temperatures based on the historical relationship between temperature and deaths in England. This tells us whether heat-associated deaths were higher or lower than expected, adjusting for whether it was a hot or cool summer.
Other factors that may influence the number of heat-related deaths include public awareness and how people respond during hot weather, as well as conditions like warm nights, which can make it harder for the body to cool down and recover, intensifying the impact of a heatwave.
The report on summer 2024 has included new breakdowns of heat-associated deaths. For the first time, the number of deaths has been calculated for different settings, such as in the home, in care homes and hospitals. There are also new splits for local areas and for different underlying causes of death. This allows us to gain a clearer picture of the impacts of heat on health across the population.
Key findings of the 2024 report
During four periods of heat in 2024, there were 1,311 heat-associated deaths in England. This was 282 more deaths than predicted, based on the observed temperatures and historic temperature-mortality trends.
The highest mortality rates were seen in people aged 85 years and over, followed by those aged 75 to 84 years.
More deaths occurred earlier in the summer than in the later heat episodes.
Importantly, significant heat-associated deaths were observed in 3 out of the 4 heat episodes, even though only yellow Heat-Health Alerts (the lowest alert threshold) were issued during these periods.
These findings show how even moderate heat can result in serious health outcomes and mortality, especially for older adults.
Yellow alerts matter
While red and amber alerts naturally grab attention due to increased media coverage, yellow alerts are still significant. They signal that the weather could have a real impact, especially on people who are more vulnerable, such as older adults, babies and young children, and those with certain pre-existing health conditions.
The 2023 and 2024 heat mortality reports both highlight that significant heat-associated deaths occurred during yellow alert periods. This shows that action is needed across all alert levels, not just during extreme heat events. Heat doesn’t have to be record-breaking to be dangerous for some.
Working together for a safer summer
We all have a part to play in reducing the health risks from high temperatures and potentially saving lives. Checking in on those at higher risk of becoming unwell in hot weather and following public health advice can make a big difference.
Staying informed and prepared is more important than ever, especially as annual global temperatures continue to rise which could lead to even higher numbers of heat associated deaths as indicated in the Health Effects of Climate Change report.
You can sign up to receive Heat-Health Alerts directly from UKHSA by email here, helping you stay one step ahead of rising temperatures, and the current alerting status can be found on UKHSA’s Data Dashboard.
Warm weather is something many of us enjoy, but heat remains a serious health risk. The good news is that with better data, clear warnings, and simple actions, we can reduce its impact and help everyone stay safe and well.