Should I pee or hold it to stay warm?

[marcusl]

Keep in mind that your body reduces circulation to the "extremities" (that's arms and legs) when cold in order to reserve heat for your core organs. That, coupled with the large ratio of surface area to volume, is why frostbitten fingers and toes are so common. Heat flux from extremities is lower than from torso and head, giving some support to the proportion of body heat lost from the head in the cold.

 

[Jacinta]

I'd imagine if you were lost you'd hold your pee in not because it'll keep you warm but it'll dehydrate you if you pee and you have no access to water.

 

[WWGD]

I'd imagine if you were lost you'd hold your pee in not because it'll keep you warm but it'll dehydrate you if you pee and you have no access to water.

I have seen some e.g. survivalist Bear Grylls (sp?) even suggest under certain conditions one drink the pee to hydrate or lower risk of dehydration.

 

[BillTre]

it'll dehydrate you if you pee and you have no access to water.

Actually, once urine is in the bladder, I don't think there is much water re-uptake of water from the urine. That's what the kidney is made for. However, the kidney is upstream of the bladder which stores and accumulates the kidney output.
The urine in the bladder is already separate from the other fluids of the body (within which dehydration would have its effects on overall health).
Kidney function can be controlled by normal and diseased bodily functions, as well as medicine (I assume).
Over longer terms than just having to go pee, effecting these control mechanisms might either produce or prevent dehydration.

 

[DaveC426913]

Agree with Bill. I don't think holding your pee will mitigate dehdyration.

On the other hand,
1] the muscle effort to hold in your pee will burn calories unnecessarily.
2] the risk of accidentally wetting yourself increases greatly - and that can have lethal consequences in a frigid survival situation.

 

[gary350]

Interesting, to pee or not to pee, that is the question.
A kettle heats half a kettle faster than a full one?

If both kettles are 98 degrees, a kettle still heats half a kettle faster than a full one.
When I was young I had hair I never wear a hat. Now I have no hair and always wear a hat.

 

[DaveC426913]

If both kettles are 98 degrees, a kettle still heats half a kettle faster than a full one.

That is an inapplicable analogy to retaining body heat.

 

[Rive]

Over longer terms than just having to go pee, effecting these control mechanisms might either produce or prevent dehydration.

For example coffe or alcohol (any form). Worth mentioning that the short warm feeling from alcohol in cold might have a high price in severe conditions: both in dehydration and in losing 'core' heat in increased rate - since alcohol does not produces heat, but helps to lose it (by warming up your skin).

if you're in snow-land there's frozen water so you won't die of thirst --

'Drinking' ice also comes at the price of lot of lost 'core' heat. The amount of heat required to melt ice is no joke. So while the 'pee or not' will not matter directly, 'drink or not' does in case you have only something cold to drink.

I have seen some e.g. survivalist Bear Grylls (sp?) even suggest under certain conditions one drink the pee to hydrate or lower risk of dehydration.

Urine usually has a relatively high salt concentration. Drinking salted water in survival situation - in general, that's a very bad idea.

 

[DaveC426913]

'Drinking' ice also comes at the price of lot of lost 'core' heat. The amount of heat required to melt ice is no joke. So while the 'pee or not' will not matter directly, 'drink or not' does in case you have only something cold to drink.

Yes. It's a balancing act, dependent on circumstances. But there's little point in keeping warm if dehydration results in your being unable to care for your survival needs.

Urine usually has a relatively high salt concentration. Drinking salted water in survival situation - in general, that's a very bad idea.

In long term, yes. Like at sea. But again, an immediate threat of dehydration (and resultant loss of faculties required to survive) might be more immediate than longer term problems with drinking urine.

For example, rehydrating with urine may give to the ability to get to better shelter or build a fire, whereupon, you can then get fresh water at your leisure.

 

[neanderthalphysics]

One way of looking at it, is when you pee, you increase the surface area of your "body (+ pee)" and therefore increase the rate of heat loss.

 

[gary350]

Assume a person weighs 200 lbs the average person pees about 6 oz. 3200 oz vs 6 oz pee is .1875% of your body weight. Assume your lost in the wilderness in freezing weather 6 ounces of 98 degree liquid probably won't keep you alive more that several extra minutes.

 

[WWGD]

Ultimately it may be more useful to determine the factors that have the largest weight over the outcome( survival). I doubt there have been many cases where someone died because they decided to pee. To paraphrase someone in this post ( I think it was @pinball1970 ), to pee or not to pee is not the question. Edit: Maybe we should look into those final 10 to complete a 360 , Gary ;).

 

[pinball1970]

One way of looking at it, is when you pee, you increase the surface area of your "body (+ pee)" and therefore increase the rate of heat loss.

Lots of ways of looking at this and from a biological/physics point of view I think this has been illustrated in the posts.
One last thought from me, retaining urine gives increase risk of cystitis. As per @DaveC426913 just let it go, stress of retaining probably out weighs some of the very slight thermodynamics advantages.
More importantly I honestly thought my Hamlet quote would have got at least one tip of the hat. That was mildly clever and also slightly funny. Slightly.

 

[WWGD]

Lots of ways of looking at this and from a biological/physics point of view I think this has been illustrated in the posts.
One last thought from me, retaining urine gives increase risk of cystitis. As per @DaveC426913 just let it go, stress of retaining probably out weighs some of the very slight thermodynamics advantages.
More importantly I honestly thought my Hamlet quote would have got at least one tip of the hat. That was mildly clever and also slightly funny. Slightly.

Us nerds don't always have time for fun, Pinball.

 

[pinball1970]

Us nerds don't always have time for fun, Pinball.

There is a sliding scale, I put @PeterDonis @Dale @Vanadium 50 at the more serious end and the likes of @phinds @berkeman @DaveC426913 @DennisN at the other. Unless someone posts something stupid, unverified or personal theory without searching then everyone on here can go full terminator mode.

 

[Andrew Mason]

Which will keep you warmer, pee or hold it?

I would suggest that you do both if you have a water tight container like a plastic bag. Pee into a plastic bag and hold it just under the outer layer of your clothing or your coat but not next to your body until it freezes completely. Each millilitre of urine will release about 490 Joules of heat energy into the air space between you and the outside air as it cools and freezes.

AM

 

[sophiecentaur]

recent studies attempted to reproduce the effect and concluded that, per unit skin surface, heat loss via the head was no more than anywhere else on the body.

I am always alerted by the word "studies". They can vary in integrity and according to the original ideas of the 'studier'. Would a fair test involve naked bodies, arctic explorers, divers or people standing at a bus stop in winter?
People with any sense do not go out in cold conditions without good head gear so the 40% figure is a good frightener to encourage wearing the right clothes, even if it is a bit approximate.
When I am poorly in winter, I often wear a woolly hat in bed and that makes me feel a lot less bad.

 

[Baluncore]

Over longer terms than just having to go pee, effecting these control mechanisms might either produce or prevent dehydration.

Agree with Bill. I don't think holding your pee will mitigate dehdyration.

I do expect back pressure from the bladder on your kidney ion exchange membranes will reduce the volume of urine produced. That may be important if it reduces the rate at which you must eat snow to rehydrate.

When I am poorly in winter, I often wear a woolly hat in bed and that makes me feel a lot less bad.

When sleeping in the cold, put on a hat, but also take off your socks. That either reduces blood flow restriction in your feet, or reduces peripheral heat loss. Feeling cold is a feeling, it is more important to retain core warmth. The final response to hypothermia is feeling hot and stripping off clothing.

 

[sophiecentaur]

but also take off your socks.

I think the philosophy of bed socks is that they are deliberately over sized so you get the benefit of insulation without strangulation. I get cold feet in bed and in winter, the big loose socks are just brilliant. My temperature regulation is really rubbish and I 'feel' hot or cold long before the other people with me. (In bed, that's just a single person Lol)

 

[DaveC426913]

People with any sense do not go out in cold conditions without good head gear so the 40% figure is a good frightener to encourage wearing the right clothes, even if it is a bit approximate.

That's a very different argument.
That's not a scientific view, that's political view - an attempt to sway others' understandings away from facts and toward what you think they need to hear.

Why not just make it 100%? It's a slippery slope you choose to walk.


Other examples:

 

[sophiecentaur]

That's not a scientific view, that's political view

I couldn't disagree with you - particularly if there were some really hard facts to the contrary.
That 40% figure is not associated with any particular conditions and, of course, it basically advises people,in an overstated way, to wear head covering. If I were to try to sleep out of doors in a proper five season sleeping bag with my head uncovered, it wouldn't surprise me if my head was losing the 40%. I have been in milder conditions than that and my head actually hurt with the cold.
But this isn't Physics and I don't think it can be made into Physics.

 

[DaveC426913]

... this isn't Physics and I don't think it can be made into Physics.

Except that's what it is sold as - what with quoting studies and providing percentage of heat loss.

Those are verifiable - and, notably, falsifiable - claims.
i.e. to state it as fact that "studies have shown 40% etc. etc." is actually a lie.

 

[sophiecentaur]

is actually a lie.

I think you are taking this too seriously for a bit of idle chat.
The 'studies' have not been cited but that doesn't mean they don't exist so calling the statement a lie is over the top, I think. Incorrect doesn't mean a lie. The Science may be bad and the evidence may be dodgy so far but I reckon I could arrange an experiment in which the 40% figure would apply. Insulation fabric can be pretty damn good and the ratio of surface areas of body and head is not great. A 'study' along those lines would produce quotable results which would not involve a 'lie'. Bad Physics and with possible H and S risks but on the right side of safe information.
Isn't this along the same lines as recommended maximum salt and alcohol intake figures and a whole lot of other medic - driven rules? Erring on the safe side is forgivable - much more forgivable than telling people that smoking is harmless. etc. etc.

 

[Laroxe]

Hmm.. I've never really thought about this one but as I read through the answers I thought there was some strange responses. The physics of the rate of heat lost from urine is all really irrelevant when you consider how the temperature is controlled carefully in the body, it is essentially irrelevant to our thermoregulation. Very cold conditions cause vasoconstriction this changes various psychological parameters which our body compensates for by increasing diuresis. So give it time and no choice will be needed. Someone mentioned that opening your pants will effect insulation but even this will depend on the amount of flesh exposed and anyone who claims this is significant in their case clearly isn't worth listening to.:)

The stuff about heat loss from the head is also interesting, its true that someone just in bathing trunks only looses around 10% of their heat through their head but again someone commented on the value of this information in the average survival situation. In a well insulated person the head is often the least well protected and it does have a very rich blood supply it does seem that following heat loss from the head the core body temperature drops more quickly than would be expected presumably because of the blood flow. It also seems that if only the head is exposed to the cold this doesn't activate shivering.
Its hard to identify a single factor that has the most important impact on the risk of hypothermia but if you have a pee and manage to pee all over yourself, being wet must be among the top contenders.

 

[Rive]

Someone mentioned that opening your pants will effect insulation but even this will depend on the amount of flesh exposed and anyone who claims this is significant in their case clearly isn't worth listening to.:)

It's just you likely not had a good all day hike in weather below -20°C, with both trousers and under trousers, paired with a long, thick coat, sweater and stuff.
Takes its time both to loosen all that up and to warm up afterward... And you will think twice next time to hold it or not

 

[DaveC426913]

I think you are taking this too seriously for a bit of idle chat.

I think the reason it's been brought here, to PF, and put in the Bio/Med forum is to separate fact from myth. This wasn't posted in GD.

The 'studies' have not been cited but that doesn't mean they don't exist so calling the statement a lie is over the top, I think.

The studies are cited, lending a false air of authority to the myth that makes it look like it's fact.

Incorrect doesn't mean a lie.

I am not deliberately blowing this out of proportion just for drama's sake. I didn't start out using the word 'lie' until I started to see internet urban legend being defended - and here on PF no less.

This is exactly the opposite of what PF stands for.

The Science may be bad and the evidence may be dodgy so far but I reckon I could arrange an experiment in which the 40% figure would apply. Insulation fabric can be pretty damn good and the ratio of surface areas of body and head is not great. A 'study' along those lines would produce quotable results which would not involve a 'lie'. Bad Physics and with possible H and S risks but on the right side of safe information.
Isn't this along the same lines as recommended maximum salt and alcohol intake figures and a whole lot of other medic - driven rules? Erring on the safe side is forgivable - much more forgivable than telling people that smoking is harmless. etc. etc.

I'm not sure why you're defending such methods. PF is supposed to be a refuge of rationality and fact over emotion and myth.

 

[Rive]

I'm not sure why you're defending such methods.

Your lack of understanding about what 'practical approach' is starting to be rather disturbing.

Taken the study you prefer to call 'fact' as a starting point it takes a lot of completely unnecessary, hazy and dubious calculations over unclear data (clothing and temperature details and such) to get back to the usable 'around 40%'. It would be very refreshing to see you attempt to follow through with all that before so easily calling a direct attempt to provide an useful result a 'lie'.

 

[Mark44]

One way of looking at it, is when you pee, you increase the surface area of your "body (+ pee)" and therefore increase the rate of heat loss.

This makes no sense. Your volume is decreasing, so there will be a (marginal) decrease in surface area.

 

[Mark44]

That's not a scientific view, that's political view

How is that a political view?

to state it as fact that "studies have shown 40% etc. etc." is actually a lie.

I think you are taking this too seriously for a bit of idle chat.

I agree.

The 'studies' have not been cited but that doesn't mean they don't exist so calling the statement a lie is over the top, I think. Incorrect doesn't mean a lie.

I agree with this, as well.
It could be that the 40% figure overstates the amount of heat loss when the head is uncovered, but I doubt that the figure is off by as much as a factor of 2.

Newton's Law of Cooling states that the rate of change of cooling, per unit of time, is proportional to the difference between the object's temperature and that of the ambient environment. Even though the head's surface area is relatively small in comparison to the total surface area of the body, the difference in temperatures between the head and environment vs. those of the rest of the insulated body and environment are much greater. This means that the head will be losing heat at a greater rate per unit area than will the rest of the body.

In any case, all of this discussion of how much heat you lose by not wearing a hat is off-topic.

 

[jedishrfu]

I think you are taking this too seriously for a bit of idle chat.
The 'studies' have not been cited but that doesn't mean they don't exist so calling the statement a lie is over the top, I think. Incorrect doesn't mean a lie. The Science may be bad and the evidence may be dodgy so far but I reckon I could arrange an experiment in which the 40% figure would apply. Insulation fabric can be pretty damn good and the ratio of surface areas of body and head is not great. A 'study' along those lines would produce quotable results which would not involve a 'lie'. Bad Physics and with possible H and S risks but on the right side of safe information.
Isn't this along the same lines as recommended maximum salt and alcohol intake figures and a whole lot of other medic - driven rules? Erring on the safe side is forgivable - much more forgivable than telling people that smoking is harmless. etc. etc.

From LiveScience they debunk the myth of 40% heat loss, A more recent experiment in 2006 showed it to be 7-10% in the British Medical Journal:

https://www.livescience.com/34411-body-heat-loss-head.html
https://www.bmj.com/rapid-response/2011/11/02/head-cover-cold