This story has been updated. It was originally published on 2 August 2018.

During heatwaves, everyone has plenty of tips on how to keep cool. But which tips and facts stand up to scientific scrutiny on the hottest days of the year? We look at the evidence for whether you should:

1) Stick to cold rather than hot drinks

Drinking plenty of liquid is the right thing to do during a heatwave: it’s essential to stay hydrated to protect the kidneys. But there is debate over whether that drink should be ice-cold or hot.

The theory behind choosing a hot drink is that it temporarily heats you from within. This causes you to sweat more, which cools you down. The human body can produce up to two litres of sweat per hour, which is an effective way of reducing your core body temperature.

But if that liquid is not replaced you soon become dehydrated – so some recommend avoiding hot drinks altogether. Some also argue that you shouldn’t have too much tea or coffee, as these contain dehydration-causing caffeine. However, there is little evidence that moderate amounts of caffeine act as a diuretic.

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It’s true that some research has backed up the idea that cold drinks are better. There have been studies where people undertook vigorous exercise and then had their core body temperature measured while drinking hot or cold drinks: it was found that cold drinks were the most effective at cooling them down.

But there is one possible problem with these findings and that’s the the method used to measure the temperature. The brave volunteers were given rectal thermometers. As Ollie Jay, associate professor in thermoregulatory physiology at the University of Ottawa, has pointed out, the liquid from a cold drink goes straight to the stomach, not far away from the rectal thermometer. It’s little wonder, therefore, that the temperature appears to go down.

When his team experimented with taking measurements from eight thermometers on different parts of the body instead, they found that hot drinks cooled the body more because they increased the sweat response, as predicted.