How dangerous is excessive heat?

We’re all feeling it – it’s hot. Public Health England has extended its heat-health alert until Friday 23 July, and we’ve clocked temperatures that mean we’ve had a run of the hottest days of the year – at Heathrow Airport the day I’m writing this, temperatures hit 32.2°C. As a result, the Met Office have issued extreme heat weather warnings, and told people to watch out for sunburn and heat exhaustion. If you’re like me, the heat has had you all sweaty and likely messed up your sleep, but what else can it do? How dangerous is excessive heat, and what can we do to mitigate it?

Our bodies are clever, and they aim to keep a core temperature of around 37°C no matter the weather – if it deviates from this, it has a solid range of efficient physiological mechanisms to try to put it to where it should be. When you’re cold, for example, your body starts to shiver – this is an attempt to generate heat by allowing muscles and organs to shake within the body. When we’re too hot, the body has to maintain core temperature by losing heat, and it has a number of strategies for this.

Blood vessels supplying blood to the skin dilate – this allows more warm blood to flow near the surface of the skin, where the heat can be lost to the air (this, incidentally, is why some people’s skin look redder in hot environments). This heat can be lost through sweating, which cools the body as it evaporates. And, of course, rest is extremely important for reducing heat production – about 80% of the energy produced by working muscles is heat, so resting reduces the amount of heat produced and, thus, the amount that needs to be lost.

 Our bodies are clever, and they aim to keep a core temperature of around 37°C no matter the weather

However, if you’re in a hot and humid place, some of these strategies don’t work as well. If it’s humid and you’re covered in sweat, the sweat isn’t evaporating, and that means you aren’t getting the cooling you need. The heart realises this, and starts to beat faster, trying to pump more blood to your skin – as the blood vessels open up, your blood pressure decreases and the heart has to work harder. As this happens, you’re losing fluids and salt (and the balance between them) – this combination of factors can lead to heat exhaustion. Symptoms include dizziness, nausea, swollen ankles, headaches, and tiredness.

If someone has heat exhaustion, the best thing to do is to try and cool them down. Move them to a cool place, get them to drink lots of water, and cool their skin – if they can be cooled down within half an hour, heat exhaustion is not normally serious. If they don’t recover, what follows is heat stroke, a medical emergency that requires urgent attention. The body’s temperature can rise above 40°C, potentially leading to seizures and loss of consciousness. It is caused by a failure of the hypothalamus, the region of the brain that coordinates our response to excessive heat, and sweating may stop as a result. In the worst-case scenario, patients with heatstroke can experience irreversible brain damage, multiple organ failure, and death.

Heat is no laughing matter – in 2003, a European heat wave lasting two weeks killed an estimated 15,000 people in France, and 70,000 throughout Europe. Around 600 people die in the USA every year of heat-related illness, and that number rises to 2,000 in England. Although some groups are more at risk – older people and those with long-term conditions are less able to cope with the strain heat puts on the body– everyone can be affected.

So what should you do to cope with the heat? Find a cool spot indoors or in the shade, put on light clothing, and avoid physical exertion if you can. Putting a damp cloth on your skin or immersing yourself in cold water are good strategies for remaining cooler, and drawing the curtains is a good idea if it’s hotter outside than in. Whatever happens, make sure to stay well hydrated – fluids are important to keep you cool, and to help replace the water you lose to sweating. Most drinks are good (as are foods with high water content), but steer clear of excessive alcohol.

It’s easy to see heat as an annoyance that gets in the way of everyday living, but it can be genuinely life-threatening if you don’t take it seriously. As global temperatures start to rise, we may now need to start adapting to the heat in order to protect ourselves, so bare some of these tips in mind and stay safe.