I am vaguely familiar with the physics of sweating – why it cools you off. Something about the energy used to evaporate the liquid.
If I am sweating, and I wipe off the sweat, am I removing that sweats ability to cool me off? Does the fact that there is now more room on my skin for new sweat to appear helpful?
Counterproductive to wipe it.
The sweat cools you faster while it is on you. Besides scientific evidence, di you ever get the cold sweats…where you sweat so much you get chilly (cold sweat when body temp regulator is screwed up)
Sweat inside then head outside…much colder!
I think the evaporation is the cooling process.
Yes, sweat cools you off primarily by evaporation. Wiping it off so you will have room for additional sense makes no sense. The air will evaporate the perspiration and you will replace it with more sweat. If you wipe it off, there is no evaporation to cool you off. Conduction and convection are also involved.
Unless it’s dripping into your eyes. That’s the worst thing about going bald.
Are you sure about that? Then why do you feel cooler when you wipe it off?
Because it really ain’t that counter-productive. Sweating is not a precision science, people. The amount sweated often has little to do with the core body temperature and the desire to cool the body down, and more to do with hormone levels, social situations, and drug effects (tobacco and alcohol, to name but two).
When you wipe it, you actually reduce the volume of sweat, and the thin film left evaporates more quickly, cooling more effectively at that particular moment. If you’re planning a marathon sweating session, then the effects may be slightly counter-productive, but not much.
There is some science to back up the claim that you feel cooler when you do it. What Qadgop described is the reason why you feel cooler, which is the same reason why if you blow hot or cold air across the surface of hot coffee it will get cool.
Ditto QtM. When too thick of a layer of sweat builds up, the outer layer is evaporating and cooling just to top layer of sweat. You basically want a one molecule layer of sweat going. So take your laser, diffraction grid, half-silvered prism and micrometer to the gym next time.
“Sweating is not a precision science” Gotta love this board.
Hypothesis to be proved: The greater the amount of sweat on the human body the greater the cooling effect.
Premise 1: Evaporation, convection, conduction, and radiation are all factors leading to a cooling effect. Radiation is based upon the dilation of the blood vessels and so is not relevant to this proof.
Premise 2: The greater the relative humidity the less that will be evaporated in any given time span. If the RH is 100%, there is no available moisture to be given to the surrounding air. Hence, “It ain’t the heat; it’s the humidity.”
Premise 3: Convection and evaporation will be affected by the wind speed. Conduction will be affected by the temperature differential between the surface of the body and the surrounding air.
At any given time frame, the RH, wind speed, and temperature differential will be the same. So, we can disregard the cooling effects of convection, conduction, and radiation.
Since, therefore, the rate of evaporation is dependent upon the RH, at any given time span with any given RH, the amount of evaporation depends upon the amount of water available to evaporate. The amount of evaporation is a factor in the cooling effect.
Therefore, the greater the amount of sweat on the human body, the greater the cooling effect. QED.
Logically, wiping sweat off reduces the water available for evaporation, so it shouldn’t cool you off.
However, I swear that I feel cooler once I do, especially if there is wind blowing.
So, maybe when sweating profusely, it tends to build up in streams and drops where evaporation isn’t very efficient. If using something (especially a non-absorbent hand) to wipe it off, maybe some of it is wiped away, but the rest is spread over a thin film, covering areas that weren’t wet enough for good evaporation, thereby giving more suface area to evaporate and therefore a cooler feeling.
Alternately, the areas that don’t have a big bead of sweat may be saturated with salt. Water saturated with salt evaporates more slowly, so wiping sweat off mixes the (presumably) non-saturated big drip with the film of saturated sweat, so the sweat suddenly starts evaporating faster again.
But right or wrong, only the very outside layer of water molecules will evaporate, so having excess sweat (big drips) aren’t really going to help (at least from the evaporative side) and will just fall off anyway, so as far as wipe vs. non wipe, it doesn’t matter much.
Sorry, barbitu8, I go with Qadgop.
You’ve proven that a greater amount of sweat will cause a greater amount of cooling, but you haven’t identified what it is that is getting cooled off.
It seems to me that if a thick layer of sweat is on the skin, it does not all evaporate at once. Only the surface molecules evaporate. This cools down the remainder of the sweat, not the skin.
For maximum cooling of the skin it seems to me the the best results occur with a very thin layer of sweat (such as will be generated a few seconds after you wipe away the thick layer). That thin layer will evaporate quickly and cool off the skin, and be replaced by another thin layer.
Unfortunately, as it has been so aptly said here, “sweating is not an exact science”, and the body frequently overproduces, relying on our brains to figure out how to get rid of the excess.
Another reason why wiping may make you feel cooler: One of the cues that tells you that you’re hot in the first place is sweat. Before wiping, your forehead is covered in sweat, and you think “Wow, my forehead’s all sweaty, it must be hot out!” After wiping, you think “Good, no more sweat. That’s much better.”.
Not necessarily. Sure on a hot day, the sweat will be replaced immediately by more sweat. But you can sweat, and do sweat, on cooler days. I’ll come back from running when it’s near freezing with a T-shirt soaked in sweat. Now, if you wipe sweat off on a day like that, it will take time for it to be replaced by more sweat. OTOH, you say, who needs to be cooled on those days? But that’s not the issue. (Actually, when I lived in Illinois, I’d have icicles hanging from my chin.)
Further, if the sweat underneath the top layer is cooled, by conduction, that cooling will be transmitted to the skin.
Yes, but that cooling rate will be smaller than if it sweat was evaporating straight from the skin. The reason is that the surface of a thick layer of water must be cooler than the skin, so the rate of evaporation (=rate of cooling) is reduced.
I have a related question: is salt being secreted from the skin even when the skin is not wet with sweat? That is, when the skin is apparently dry, is sweat coming out of the cell and the water content evaporating, or is the salt staying in the cells and just the water vapor escapes from the cells?
chronos is going the right direction on this.
How many things do we do with our body for the purposes of efficiency?
I wipe sweat off because it bugs me. Bugging me is counterproductive. I couldn’t care less that my body thinks it’s 9/10th of a degree hotter than it should be. Suffer in silence.
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and now… the technical answer. Wiping off sweat dissipates heat. Less heat than if you’d left the sweat alone until it was really hot.
On the other hand, if “wiping” means you’re spreading the moisture around, increasing evaporation rate, and faster evaporation is just what you want…then it’s productive.
The factor that hasn’t been introduced is “how much water does your body have?” Is there a nearby cooler with Diet Croak? If you’ve got gallons, the sooner you get rid of that sweat, the better. If you’re in desert with no water, you don’t want to sweat at all. Certainly not wipe it off!!
Hmmmm, call me a stickler for the OP, Qagdop and Company:
He asked if wiping sweat away so that there is room for new sweat to appear is couterproductive.
It is counterproductive. You have acknowledged that some sweat is good…maybe too much is LESS efficient, but that is changing the basics, which usually have to be ‘qualified’ by answering…
“generally speaking, it is counterproductive to wipe sweat away because you are removing the sweat and preventing evaporation, however if you could manage to wipe away most of the sweat and leave a thin layer behind, you might make your sweat more efficient”
While that is cute, the gist of the issue is: Will wiping sweat away be counterproductive? And the answer is “yes”.
Sweat may well be there without your knowing it. Some swimmers say they don’t sweat. They do, but the water washes it away and they don’t realize it.
My sweat is not salty because I don’t take in too much salt. I don’t use salt at all. Most products have some sodium. If you find your sweat salty it may be that you are taking in too much sodium. Sweat may drip in my eyes but since there is little or no salt in it, it doesn’t sting as much.
As you exercise, you have to use muscles, of course, which means there is an exchange of ions (sodium and potassium) occurring in the nervous system, but if you don’t have too much salt in your body, IMHO little if any will be in sweat. Perhaps ** QAGDOP ** or others who know can enlighten me.
Thanks ** PHILSTER ** for essentially agreeing with me. A rare occurrence. 
AHA! Because oil films prevent evaporation!
If your sweat layer is topped by a few molecules layer thickness of skin oils, then evaporation halts. Wiping off the sweat does not remove it all. Even a squeegee won’t dry your skin.
Try this: pour identical water into two identical pans, then drip a single drop of veg oil on one of the pools of water. Wait a couple of hours. Then feel both pans. The non-oily pan will be distinctly cooler. (Might not work in high humidity conditions.)