What extreme heat can do to your body – and how to stay safe

·8 min read
A man lies in the sun at Primrose Hill, in London, Britain - Peter Nicholls/REUTERS
A man lies in the sun at Primrose Hill, in London, Britain - Peter Nicholls/REUTERS

Heatwaves generally conjure thoughts of lazy afternoons pottering in the garden, lounging by the sea or on the hunt for ice cream. But there’s a darker side to record temperatures: heat kills.

The Met Office issued the first ever national red alert for heat in July, with further high temperatures in August, while the UK Health Security Agency has warned “illness and death may occur among the fit and healthy, not just in high-risk groups”.

It’s not an empty threat. Excess death figures show that 1,634 people died due to heat in 2021, during what was a “fairly unremarkable” summer in terms of temperature. In 2020, when the mercury hit 37.8 degrees celsius, the toll reached 2,556.

Experts say the current prolonged heatwave – especially the “tropical nights” where temperatures remain above 20 degrees – could be even more deadly.

“The risk now is far bigger, as this period where we’re going to have over a week of temperatures in the high 20s and 30s is exceptional,” said Bob Ward, director of policy and communications at the London School of Economics’ Grantham Research Institute for Climate Change. “I’m afraid we’ll probably be seeing a high number of deaths across the whole of Europe, and it could well approach what we saw in 2003.”

A burnt house at Mouta on July 15, 2022 in Alvaiazere, Portugal - Octavio Passos/Getty Images
A burnt house at Mouta on July 15, 2022 in Alvaiazere, Portugal - Octavio Passos/Getty Images

That year, sweltering temperatures spanned the continent between June and August, and an estimated 70,000 people, mostly elderly, died – more than 15,000 in France alone. It caused many governments, including the UK, to create heatwave plans to tackle hot spells in future.

But how do people actually die from heat, who is most at risk – and how do you protect yourself?

The health dangers associated with high temperatures are split into two main stages, said Martin Berry, chief paramedic officer at St John’s Ambulance. Many of us will have experienced the first: heat exhaustion.

“You start to feel quite dizzy, have excessive thirst and become quite sweaty,” he said. “It’s usually a sign that you’ve been out in the sun too long, or exerted yourself and your body temperature has increased too high.”

This isn’t normally serious, as long as you can get out of the heat and cool down. But if you don’t and your body temperature continues to rise, you enter the heat stroke danger zone. And at this stage your system struggles to self regulate, and the situation can deteriorate rapidly.

An old wheel is exposed on the riverbed at low tide in the Carew River which runs alongside Carew Castle on July 11, 2022 in Pembrokeshire, Wales - Matthew Horwood/Getty Images
An old wheel is exposed on the riverbed at low tide in the Carew River which runs alongside Carew Castle on July 11, 2022 in Pembrokeshire, Wales - Matthew Horwood/Getty Images

“Problems really begin when your core temperature reaches the 40 degrees celsius level,” said Mr Berry. “One of the signs you see is that blood vessels start to expand, which means blood pressure starts to drop and less blood is delivered to primary organs. So they’re getting less fuel – less oxygen and sugar – and that will have an impact on normal bodily functions.”

The brain, which is “responsible for all the safeguarding mechanisms that keep us cool”, is particularly hard hit, and starts to misfire as it can no longer process the glucose it needs to function effectively. People also become red, warm to touch, confused and may lose consciousness. Their ability to sweat is also hindered – a problem as this helps the body cool down.

“At this point it’s a medical emergency,” said Mr Berry. “Sometimes a lack of glucose and oxygen to the brain can push someone into seizures… and the body’s normal regulation – things like the heart rhythm – become ineffective.”

“It’s like when a laptop gets too hot, it starts to do all sorts of weird and wonderful things,” he added. “The part of the heart that regulates normal rhythms starts to become too fast, too slow, or a combination of both. That irregularity can end up triggering cardiac arrest, where the heart cannot pump effectively – and that is immediately life threatening.”

In most cases of heat-related deaths, it is a cardiac arrest that proves fatal. But strokes are also common, especially if someone becomes severely dehydrated.

“When your body temperature rises and rises, your system starts to go into a vicious circle – you get cardiac insufficient, brain insufficient, and there aren’t enough fluids,” said Dr Bharat Pankhania, a senior clinical lecturer at the University of Exeter Medical School.

“If you haven’t kept hydrated, your blood gets sticky, and that sticky blood forms clots. If they form in what we call end terminal arteries – the heart, brain, gut – then that part of the organ starts to die. That’s a stroke.”

According to the World Health Organization, deaths and hospitalisations related to heat “can occur extremely rapidly (same day), or have a lagged effect (several days later)”. The agency added that even a small divergence from average seasonal temperatures can have a major impact, while extreme changes can also worsen pre existing chronic conditions, such as diabetes.

A man swims in the Sky Pool, a transparent swimming pool suspended 35 meters above ground between two apartment buildings, during hot weather in Nine Elms, central London - Victoria Jones/PA
A man swims in the Sky Pool, a transparent swimming pool suspended 35 meters above ground between two apartment buildings, during hot weather in Nine Elms, central London - Victoria Jones/PA

The elderly and young children are most susceptible to heat, experts added. According to the UKHSA, nearly 90 per cent of the 1,634 heat related deaths in 2021 were among those older than 65. Experts fear that many of these people died quietly at home.

“At the extremes of age – so therefore this applies to little babies and elderly people – the thermal regulatory system is not as finely tuned as it should be,” said Dr Pankhania. “The biggest trouble is that this system doesn’t send the elderly the signals that they’re getting hot and need to do something about it – so their core temperature rises, then rises again.”

Mr Berry added that the elderly also have less body fluids stored up as a backup, which means “they get into the heat stroke window more quickly, as there’s less of a buffer when they get dehydrated”. They may also be on medications, such as blood pressure tablets, which have an impact – while it is “vital that they take them, it just means they need to be more aware to prevent dehydration”.

So how do you stay safe in the heat? Dr Pankhania said the best approach is to prevent heat exhaustion or stroke in the first place. Drink plenty of water, draw the curtains, open windows, avoid strenuous exercise, wear light clothing, stay out of the sun – and keep a close eye on young children, as well as elderly relatives or neighbours.

If someone does show signs of overheating, slowly up their fluid intake, use a rehydration sachet and take it easy. A very cold shower or fan can actually be a bad idea, said Dr Pankhania – it cools down the skin but closes the pores, making it harder for the body to cool down internally.

Instead, Mr Berry recommended dowsing a towel, bed sheet or clothing in cool water and putting it over an individual’s chest. If the situation isn’t improving, especially if someone is struggling to breath and rapidly losing consciousness, call an ambulance. Medics can help cool someone’s internal temperature by carefully administering fluids directly into the circulating blood supply.

But in the long term, experts warn that Brits are going to have to become far better at preparing for and dealing with the heat.

According to a Met Office study into extreme heat, the chance of the maximum daily temperature exceeding 35C somewhere across the UK has already risen from once every 15 years in the middle of the 20th century, to once every five years now. Meanwhile a modelling report from the London School of Hygiene in 2014 estimated that, by 2050, heat-related deaths in the UK will rise by 257 per cent.

A man sits behind a wind-break on the beach on July 15, 2022 in Deal, Kent - Dan Kitwood/Getty Images
A man sits behind a wind-break on the beach on July 15, 2022 in Deal, Kent - Dan Kitwood/Getty Images

“As a nation we need more planning and preparedness for severe climate conditions,” said Dr Chris Papadopoulos, a lecturer in public health at the University of Bedfordshire. “The best response to threats to public health is always prevention.”

Mr Ward added that the UK’s heatwave plan is “not fit for purpose”, referring to a recent review of the strategy which found that it was overly focused on “warning and informing”, rather than providing planning and material help.

As well as preparing for increased pressure on the health system, Mr Ward said ventilation needs to be improved on public transport, while temperature limits for those who work outside should be introduced.

And alongside improving insulation in houses to protect against the cold, buildings should be retrofitted to prepare for the heat – adding elements such as shutters to keep out the heat.

“The big danger to those who are vulnerable is overheating in their homes,” Mr Ward said. He added that heatwaves should be named, much like severe storms, to raise their profile.

“We need to start thinking of high temperatures as a natural disaster,” he added. “If we had 100 people dying during flooding, we’d describe it as a natural disaster. Heatwaves clearly are, too – and preventable ones.”

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