Current News 360° OLD

Hot tea can cool you down... in the right conditions Credit: Rachel Husband/Alamy

BY Gareth Rubin
The Telegraph 

 

Swelter swelter swelter. Anyone would think we lived in a hot country.

As air conditioning unit manufacturers across the globe break out their atlases to find where Britain is on the map, the public have been turning to all sorts of methods for keeping cool. Among more conventional ideas, such as plunging into the local lido or stripping down to expose as much flesh as legally possible, one old chestnut of folk wisdom has been doing the rounds of dinner party conversation: drinking hot tea cools you down, because if your insides are warmer, you don’t feel the external heat so much.

Truth or balderdash? Well, as with so many intriguing questions, it’s quite possibly a little bit of both.

In the history of tea/heatwave science, a 2012 study by Ollie Jay at the University of Ottawa’s school of kinetic sciences, was a landmark. It examined just this question and came to a firm conclusion: Yes, drinking hot tea will cool you down... but only if there’s a nice breeze.

“If you drink a hot drink, it does result in a lower amount of heat stored inside your body, provided the additional sweat that’s produced when you drink the hot drink can evaporate,” he  told the Smithsonian Magazine.

So what’s going on? “What we found is that when you ingest a hot drink, you actually have a disproportionate increase in the amount that you sweat. Yes, the hot drink is hotter than your body temperature, so you are adding heat to the body, but the amount that you increase your sweating by – if that can all evaporate – more than compensates for the the added heat to the body from the fluid.”

Dogs cool off during a swim-with-your-dog day at Saltdean Lido in Sussex Credit: Christopher Pledger

Sweat, of course, works by absorbing some of the body’s heat, and then evaporating into the air, taking that heat with it. However, for the sweat-based reduction in temperature to exceed the increase due to the hot drink, you need to let all the sweat evaporate. And that means if you’re in a hot, humid room, or you’re wearing long sleeves and trousers, hot tea’s probably not going to work.

In that case, Jay suggests the opposite course of action: “The hot drink still does add a little heat to the body, so if the sweat’s not going to assist in evaporation, go for a cold drink.”

For those who want to drill down into the mechanics of how hot drinks make you sweat, it’s not, in fact, a direct response to your core temperature increasing. We have thermosensors in the mouth and throat that seem to be the key. When they detect heat, the brain activates the sweating response.

That means, for those with nerves of steel, there’s another option, as Professor Peter McNaughton from the University of Cambridge, suggests: "Eat a very hot meal – as in chili hot – because the active ingredient in chili peppers, capsaicin, acts on the same receptors in your mouth and upper digestive tract that detect heat and cause sweating, which of course cools you down.”

No doubt the perfect option for a university rugby team desperate to prove their resilience – but for the rest of us, he has a method that’s less of a white-knuckle ride: “Putting a wet towel around your head, or around your wrists, or around any part of your body will cause cooling because of course water in the towel will evaporate. This is why a wet towel feels cool when you put your hand up against it and that will cool you down."

Or there’s always the lido, a deckchair and a mini-fan, of course