Should You Wipe Off Your Sweat?

If you’re in scorching heat, or when your body is working hard and you’ve got hot, hot sweat all over, sticky and stifling - does wiping off the sweat help you cool off? Or is it better to leave it on?

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REFERENCES

Hyperphysics:

Engineering Toolbox Mollier Diagram:

Sweat Info

Other articles:

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CALCULATIONS

Typical adult human body surface area ~ 1.5-2 m^2

Evaporation rate at 25°C and 50% humidity, slight air movement (v~.5m/s) = .35kg/m^2/hr

So in these conditions, a sweat-covered human can expect to evaporate ~.5-.75 L of water in an hour (For higher humidity (60-70%) it goes to ~.37-.5 L of water/hr). That amounts to ~0.25-0.35mm of sweat (covering the whole body) evaporated in an hour, or 6 micrometers every minute.

BUT that assumes all of the energy came from the person. If some proportion of it came from the air (~1/3-1/2?) then the person is only cooled down partially.

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[KataisTrash]

And when you're done smearing it around yourself, you can smear your sweat on others to cool them down faster too!

[KenBanksPEng]

This is why I avoid any room with more than 2 physicists.

[BackYardScience]

As a logger who works in the scorching heat of the southeast US, I can confirm that leaving the sweat on you is best. Trust me, I know by experience. If you need to wipe it away from your forehead to keep it out of your eyes, yeah go ahead. But leave the rest to evaporate and keep you cool. If your shirt gets drenched, it can be a tricky situation. Yeah, it'll evaporate, but it may hold heat under the wet shirt as well. Fanning the shirt to get air to flow through it is best in my opinion rather than taking it off. That gets air moving through it and it removes a lot of heat that way and when you stop and let it rest back against your skin it will feel much colder than before. Just some advice from a guy who's had bright green shirts go white from all the sweat that runs through them and a guy who cuts trees in the heat of the southeast for a living.

[vvoid]

This is why in cold conditions the best gear emphasises keeping you dry as much as keeping you warm. You want to manage your level of insulation to avoid sweating while active, a base layer that whicks the sweat away from your body before it evaporates, and breathability in your shell layer to keep it dry.

[theonlymegumegu]

I'm really happy you addressed the Pooling of sweat being less efficient at evaporating, but even happier you suggested smearing it all over rather than wiping, i laughed so hard at that XD

[lasiace]

My personal preferred method is to use a wet cloth to replace the sweat with regular water rather than drying it off, assuming I have access to one. Aside from the obvious benefit which is that cold water is colder than hot sweat, it also has more surface area to evaporate quickly since it beads up less, and it still helps somewhat if sweat is collecting too much on your face and also doesn't feel nearly as gross to leave on.

[alexzavoluk]

After doing lots of exercise in both hot, dry conditions and hot, humid conditions, my speculation would be that if you feel very sweaty over the exposed parts of your body, that's a sign that it already isn't evaporating well. In dry conditions I'll notice that, say, my back is very sweaty underneath a backpack, or other enclosed areas like feet and armpits, but my arms, face, etc. rarely get so sweaty I want to wipe if off, because the sweat is evaporating. In humid conditions, everything feels very wet, and it will typically stay that way even after I stop exerting myself and sit in the shade, which leads me to think it's mostly just sitting there and not evaporating. I also suspect that smearing it around wouldn't accomplish much, since the limiting factor is humidity in the air.

[hideakiDT]

As a physician myself, I should confirm that it is correct, and is commonly taught in physiology textbooks that cover heat transfering. It should be noted though that when air humidity is too high or when temperature is above corporal levels sweating doesn't do much for losing temperature (although drying yourself also doesn't), as the physics is based in the droplets of sweat absorbing heat from your body as latent heat, changing to vapor, so if air is saturated with water that sweat won't evaporate ever, and if temperature is too high sweat will be absorbing heat from the environment, thus reducing its efficiency from absorbing body heat. We're not very good at losing heat as we are at producing it

[TheSilverShadow]

As someone who's dealt with severe sweating issues my whole life, I found this video to be informative.

[toddeverson]

At some point the sweat will become so concentrated with salts that evaporation nearly ceases so wiping that mess off would make sense. I have done much roofing in hot, humid weather and I usually have to change my shirt at some point because it becomes like sea-water and never dries (not to mention the odor).

[jsange]

Bear in mind sweat isn't just water, it contains some other biological stuff, thus the smell. It's a little more viscous than water, almost counts as an oil. And physics are not gross, they're cool as shit. Biology is gross.

[ebonyblack]

This explains why you shouldn't eat/drink cold things, like snow, if you're struggling for warmth or calories. Consuming frozen things will cost your body more energy to process, and thus cost you in severe situations as your body warms it up to break down.

[z-beeblebrox]

2:20 Marlon Brando's character in Apocalypse Now, rubbing his bald head in a way that only manages to smear around the sweat: *finally vindicated*

[yoyofargo]

You have skin oils too, which will film over your sweat beads and slow evaporation. It's okay to spread that sweat around or wipe it away from your eyes.

[Layarion]

you're not making sense, if it's dripping off, that means it takes the heat away with it to the ground. don't rub it on your damn body.

[burkean]

Not addressed: salt.
after a lot of sweating, your body will be covered in salt. It feels awfully nice to get that salt off and replace it with fresh water. Want to delve into why the body puts that salt into the mix?

[robw]

I think a detail was missed. Sweat is slightly saline. As the water evaporates, the remaining sweat gets more concentrated. This concentrated sweat evaporates more slowly than dilute sweat. Is it therefore more efficient to wipe off the old sweat and sweat out new, more dilute sweat.
Seems like a calculus problem.

[DragoNate]

this video taught me how to water cool a pie.

[Tinil]

So to be clear, you're saying that we can double dip by just peeing all over ourselves?

[ericchang]

You make this video now...after that scorcher of a summer in Texas...