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Not everyone gets a winter as cold (or at the same time) as we do at SciShow, but no matter where you live, you may have wondered why venturing out into the cold often makes you have to pee more often.

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[INTRO ♪].

Internet, we need to talk about a very serious problem with doing things outside in the winter:. Constantly being interrupted by the need to pee.

It doesn’t even matter if you specifically remembered to go before you put on your coat and your scarf and your pants and your other pants and your third pair of pants. You’re like, an hour, tops, into frolicking in a winter wonderland and there it is again—your body saying “find that bathroom, boy—STAT!” It’s not all in your head. It’s called cold diuresis, and it’s a pretty normal thing: being chilled makes you produce more urine.

And although there’s some debate about the mechanism, most physiologists think it’s a side effect of how our bodies keep warm. Like many animals, one trick we use to withstand colder temperatures is to reduce the blood flow to areas that are exposed. For us, that means the tiny blood vessels in our skin constrict, minimizing the amount of blood that’s chilled by the frosty weather and reducing the effort your body has to put into keeping all the most important bits warm.

But that pushes more blood into the veins and arteries in our core, sort of like how, like, squeezing one end of a water balloon makes the rest of it bulge up. And having more blood in those blood vessels increases your blood pressure, but high blood pressure isn’t great for you either. So, to compensate, your body reduces your total fluid level by increasing the amount of water in your pee.

That explanation makes sense, but it doesn’t fit perfectly. Some scientists have found that people and other animals exposed to the cold experience this increase in blood pressure, but some haven’t—especially ones that looked at longer exposures to the cold. And researchers don’t always find the usual hormonal changes that come with an increase in urine production.

So some physiologists think the constant need to pee might have more to do with salts— at least, the urge that comes after you’ve been in the cold for a while. Your kidneys can’t work as well when they’re chilled, which prevents the reabsorption of salts from urine as it’s being produced. And that triggers what scientists call osmotic diuresis, where the saltiness draws water from your blood into your urine, making you have more pee to pee.

But that doesn’t kick in, like, the second you walk out the door, because it takes time for your kidneys to start struggling. And it actually is a big concern for people that live and work in cold climates, like troops deployed in arctic environments. But for most of us, though, cold diuresis mostly means more bathroom breaks in winter.

Which isn’t so bad, as long as you remember to replace all those lost fluids! Thank you to Valerie S, Julian Taylor, and Paul for asking this question— so many different people curious about peeing in the cold— and thanks to all of our patrons who voted for this question in our Patreon poll. If you would like to propose a question for us to answer, and gain access to all kinds of cool Patron-exclusive stuff, you can head over to [OUTRO ♪].