Don't Wipe That Sweat Off Your Brow To Cool Down Faster

For many of us, it doesn't even need to be hot before we start building up a sweat the second as we step outside. But unless you're drenched, you're better off not wiping the sweat off your head, since it can cool you down faster.

Photo by Carine06

Brian Palmer over at Slate explains the science:

Don't wipe unless you're drenched. Sweat releases heat by evaporative cooling. As each gram of sweat transitions from liquid to gas phase, it absorbs 2,427 joules of energy from the body and dissipates the heat into the environment. But if you wipe away the perspiration before it evaporates, that process will get cut short, and you'll need to sweat more just to achieve the same degree of cooling. On the other hand, any sweat that drips to the ground before it can evaporate won't do you any good, so if you're really soaked you may as well reach for the towel.

So the next time you go to mop your brow, think twice — if you're really serious about cooling off, you may want to leave those sweat beads to evaporate on their own. Of course, you can always speed up the process by knowing your body's quick cooling spots too.

Let Them See You Sweat [Slate]


    If you let the sweat run down your forehead, it will sting your eyes. I'd rather be a little hotter than have my eyes hurting from sweat.

      Beat me to it, I was about to say exactly the same thing.

      I'll +1 that, it stings like an absolute *insert expletive here*

      That's why people have eyebrows

        Eyebrows are helpful, but there's only so much sweat they can hold.

    So how come it feels so good to wipe it off.? Besides the eye thing that is. I find a build up of sweat to be quite annoying.

    Last edited 27/12/12 4:20 pm

    I suspect that this article is an example of partially or completely incorrect armchair physics. While the author is correct in stating that evaporation aids heat dissipation, wiping sweat actually leaves a fine layer of sweat that evaporates very quickly because of the increased surface area of the skin at a micro scale and increased heat inputs per unit of volume of remaining sweat. A thin covering of sweat will also mean a steeper temperature gradient between the body and the air, and therefore greater heat transfer. In a way, a thick covering of sweat creates a form of insulation. The optimum amount of sweat I suspect is a trace amount, which is exactly what you end up with when you wipe it around your body.

    The fact that we instinctively wipe sweat when it forms is probably a good indication that it accelerates cooling.

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