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When you pee in a freezing environment, you can see the warmth coming out of it by evaporation. So it might seem that holding the pee as long as possible actually helps you prevent from getting even colder through time.

So one could say that it would be wise to keep the pee in your bladder as long as possible in a freezing environment, since your body has higher total heat energy, thus it gets cold slower.

Are there any health risks from holding your pee too long?

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    Another factor is how much clothing you have to remove/how much skin you have to expose. This obviously isn't the same for everyone but also depends on what you're wearing. Physics (my field) says keep the heat in, but the little physiology I know mainly seems to tell me that the body has sneaky ways to defeat crude physics-based assumptions.
    – Chris H
    Feb 4, 2022 at 14:48
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    BTW this is probably due to peripheral vasoconstriction which reduces blood volume, and that water has to go somewhere
    – Chris H
    Feb 4, 2022 at 14:51
  • Slightly off topic: if you find yourself outdoors thinking that peeing is trouble warmth-wise, I'd take this as an important warning sign that hypothermia is lurking around the corner. Not because of the short exposure while peeing, but because you are exhausted and not sufficiently well fed. (Similarly to when you dislike the idea of drinking because the water in your bottle has ice floating in it.) Obviously, in extreme weather, pee in a sheltered place, don't stick your bum needlessly right into a blizzard. Feb 17, 2022 at 19:05

4 Answers 4

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You should pee.

Your body creates its own heat when healthy and fed and you will easily compensate for loss of 100-200g of body mass in all but the most extreme conditions.

By the time you are so cold or in such a place as to be at risk of losing a meaningful amount of core body heat from urinating, I suspect your body functions will have shut down and you wouldn't have needed to pee in the first place.

For what it is worth: alpinists, mountaineers, Everest climbers will pee and poo all up and down the mountain.

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    the other part may be that you can't be sure if someone peed on that snow last week, so it's best to boil it to be on the safe side Feb 5, 2022 at 18:34
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    That should be 100-200g, and not mg. If your only urinating milligrams you have another problem.
    – fgysin
    Feb 7, 2022 at 8:45
  • Thanks @fgysin my first draft originally said mL and I changed it incorrectly , your comment is spot on.
    – crasic
    Feb 7, 2022 at 15:14
  • These specific 100 - 200 g of body weight do not contribute at all to producing heat. At most, they have a little bit of heat capacity - which, however, is of negligible effect since body temperature is tightly regulated and 100 - 200 ml of urine are only in the permille range of the total heat capacity of an adult. In that respect, there is no difference between putting the urine out of your body or putting a bag of cookies out of your inner pocket. Feb 17, 2022 at 18:39
  • It is true that due to the huge amount of latent heat needed to melt snow it is always preferrable to drink (liquid) water if at all possible. However, "the amount of water that your body "consumes" in the metabolism necessary to heat the snow to core temp is more than the amount of water you injested" is wrong: metabolizing ("burning") carbohydrates or lipids produces water rather than consuming it. Protein metabolism is a bit more complicated in that manner (you need sufficient urine production here, but in many circumstances that doesn't translate into excess water). The tradeoff with ... Feb 17, 2022 at 18:46
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No. Your body temperature doesn’t drop because of peeing in and of itself.

Peeing makes you lose a bit of body mass which – all else being equal – can mean that you’ll get colder slightly faster afterwards, if your body doesn’t produce more heat than it loses.

Obviously peeing usually means that you’ll have to remove a few layers of clothing and stop moving for a minute or so. Both factors can lead to your body temperature dropping (further). But I’m not sure “holding it in” helps with this a lot since you’ll just have to pee longer (albeit less often).

In any case, the dangerous aspect which leads to hypothermia and death is that you are constantly losing heat faster than you can produce it. If you are dressed warm enough exposing your bum for a minute won’t be a problem. Your body temperature might drop ever so slightly and then go up again once you are wearing all your clothes. “Holding it in” could actually be dangerous since shivering can easily make you lose control and pee yourself. In which case you’ll be cold and wet …

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  • You may lose more heat as a woman who has to undo/open much more in clothing than a man to avoid getting the lower half of said clothing wet.
    – Willeke
    Feb 6, 2022 at 12:12
  • Edited to address this
    – Michael
    Feb 6, 2022 at 14:17
  • @Willeke: but then, our (female) bum also tends to have more built-in insulation ("bioprene") :-D Feb 17, 2022 at 19:01
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Urinate when you need to (and make good use of any sheltered ground you find).

You won't lose temperature, other than what's due to removing insulation for a short time.

The more important issue is that a pressing need to go will be a distraction from everything essential that you're doing. Being comfortable in that regard is safer, as you can think more clearly when your brain doesn't have to deal with a continuous "full bladder" signal.

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As long as it's warmer than -45°F, you're fine.

A single event of holding pee won't harm you. It takes several days of constant prolonged holding till you develop the condition (forgot the name) when your bladder will start sending signals it's full (even if it's not). This is reversible (even if problematic), from personal experience.

A much more imminent issue is exactly how freezing is it and what is the wind-chill? It's going to be basically impossible to find yourself at the place where peeing would be painful just due to air temperature. From experience, peeing at -40°F air (zero wind-chill) is not painful at all, merely cold. So, it probably takes another 10-15 degrees to reach that point and those places are very isolated and hard to get to.

Wind-chill can be however quite painful. Way, way, way more painful than inserting camera into your bladder at the doctor's office. I don't know if it's a cold tolerance, but I peed dozens of times at around -40°F wind-chill (it's basically omni-present for up to 8 weeks per winter here in North Dakota) and it was fine. However, once at around -50°F, the sensations and pain was quite horrendous. I could feel a quite sharp and strong pain way deep inside my body and cold spreading to other neighbouring tissue around the bladder. My bladder was still quite sensitive next morning and it was still a bit painful.

You just might prefer to choose to avoid that experience.

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