Hot Tea Cools on a Scorching Day?

National Public Radio host Joe Palca contributes to the ongoing series Summer Science. A recent program “Cool Down with A Hot Drink? It’s Not as Crazy as you Think” cited reasons why hot tea refreshes in a heat wave. Here is what he discovered:

"Obviously a hot drink makes you hotter and a cold drink makes you colder. So why would you want to get hotter on a hot day?" Peter McNaughton, a neuroscientist at the University of Cambridge, asks rhetorically.

It turns out there are nerves in our tongue and mouth that have special molecules in them called receptors. As the name suggests, these receptors receive signals from the world outside the nerve.

There are all sorts of receptors in all sorts of nerves, but the nerves in the tongue have a lot of one particular receptor that responds to heat. It's called the TRPV1 receptor.

So when you eat or drink something hot, these receptors get that heat signal, and that tells the nerve to let the brain know what's going on.

When the brain gets the message "It's hot in here," it turns on the mechanism we have to cool ourselves off: sweating.

Yes, the hot drink makes you hotter … but it does something else, too.

"The hot drink somehow has an effect on your systemic cooling mechanisms, which exceeds its actual effect in terms of heating your body," says McNaughton.

This story is part of Joe's Big Idea, an NPR experiment exploring how ideas become innovations and inventions. Follow us at Facebook.com/JoesBigIdea. And enter your big idea in our video contest.

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