Jun 20, 2005
Tea Cools You Down
At the time of writing, the UK was in the middle of a rare heatwave, and my mother, as usual, suffers when the mercury rises about 25 or so (it’s 33 here today!) and, as usual, is suggesting everyone has a nice cup of hot tea to help them cool down.
Of course, it is easy to mock the underlying physics of such a suggestion (Does Hot Tea Really Cool You Down?), and I have explained to my mother that it’s a myth, but such conventional wisdom seems to persist and someone only this morning visited the sciencebase site searching for an answer to the question, does hot tea cool you down? Or more generally “does a hot drink cool you down?” Someone, even asked the presumptuous question: “Why does drinking hot drinks cool you down?”
Bluntly, no.
However, even as a hot drink, it can make you feel refreshed even when the air is still and humid and as long as you don’t gulp it down too quickly it won’t make you even more sweaty. I guess there may be a psychological effect, if the air is warm and humid and you drink something hot, that will heat you up more and make you sweat, sweat evaporates from your skin cooling your skin, so maybe you end up feeling slightly cooler, but I’m still not convinced. In fact, sweating inflames the skin in some ways as capillaries open up and you actually feel hotter when you sweat more, unless you’ve got a very strong fan. Anyway, from the thermodynamics point of view adding a hot liquid to a cooler container (your body) will raise the temperature of the container.
Now, iced tea is a different matter – make mine a peach one! And, plenty of ice!
Of course, there’s also this well-known 19th century quotation from Gladstone
If you are cold, tea will warm you. If you are too heated, it will cool you. If you are depressed, it will cheer you. If you are excited, it will calm you.
For more on teatime etiquette, check out this item.
It’s not a closed system.
Sweating has done it’s job, as have other physiological functions to expose the body’s heat to the environment where it will radiate away more efficiently and continue to do so – because it’s not a closed system.
The same conclusions are to be drawn from experiments in extreme cold. Those with wet skin (either from sweat or falling into icy water for example) will lose body heat, far faster than the same person with dry skin.
Anon, yes sweating does cool you down. But, there is a limit and wrt to the whole “tea cooling” issue, you still haven’t accounted for the fact that you’re adding heat to the system…
Sweating cools you down, as water against the skin, which radiates heat away from the body, 20 times more quickly than if it were dry. It is particularly cooling in front of a fan for the same reason.
This is one of the reasons why it is better to take off wet clothes in extreme cold. You’ll survive longer with no clothes!
Yes, sweating does cool you down. But, it’s not 100% efficient and adding a volume of hot liquid to a system with such an evaporative cooling system will cause the temperature of the system to rise regardless. Moreover, as the level of sweating rises it becomes more and more inefficient at cooling you down if there is no effective way to allow the sweat to evaporate.
When you sweat it does some what cool you down you know!