Heat affects health in several ways. Heat exhaustion, which can include dizziness, headaches, shaking and thirst, can affect anyone, and is not usually serious – as long as the person cools down within 30 minutes.
The more serious version is heatstroke, when the body’s core temperature goes above 40.6°C. It can lead to long-term organ damage and death, with symptoms including rapid breathing, confusion or seizures, and nausea.
Heatstroke is a medical emergency and requires immediate professional attention.
Who is at risk?
Some people are more vulnerable, such as young babies and the elderly, as well as those who are more exposed such as the homeless.
Existing health conditions, including respiratory and cardiovascular diseases as well as diabetes, can also heighten risk and be exacerbated by heat.
Globally, just under half a million deaths a year are estimated to be due to excess heat, according to a 2021 study in “The Lancet”, although data is lacking from many low-income countries.
As many as 61,000 people may have died in Europe during heatwaves last summer, with a repetition feared this season.
“Heatwaves are a silent and invisible killer,” said Liz Stephens, a researcher in climate risk and resilience at Britain’s University of Reading.
“We don’t often see the impact they have had on human health until the mortality statistics are published many months later.”
Less obvious risks
Air pollution also poses a health risk, with serious potential effects from wildfire smoke, including inflammation and tissue damage.
Heat also can lead to low birthweight and premature birth for pregnant women and babies, a number of studies have shown.
There are less obvious risks, too. Dr Vikki Thompson, climate scientist at the Royal Netherlands Meteorological Institute, said extreme heat often contributes to poorer mental health, as well as a rise in car crashes and drownings.
“Heatwaves are one of the most deadly natural hazards,” she said.
Timing, location matters
Experts say more deaths occur earlier in the summer months when people’s bodies have not had a chance to acclimatise.
Location matters, too: people are at higher risk in places where they are not used to such heat, including parts of Europe.
However, there are limits, and people all around the world are at risk in extremely hot weather caused by climate change, particularly those who must continue to work in physical jobs.
“It is more important than ever that we put in place measures to limit the harm on our health,” said Dr Modi Mwatsama, head of capacity at Wellcome, a London-based global health charity.
She said this ranged from providing shade and painting buildings white, to investing in early-warning systems for climate-sensitive infectious diseases such as cholera.
What you can do
Public health agencies from Italy to the US have issued advice on keeping cool, including avoiding exertion where possible and staying hydrated.
Workers should think about having more breaks and changing their clothing, too, scientists said, adding that it is also important to check on the vulnerable, including older and isolated people.