system
Given the following post, respond as if you're commenting on Reddit:
human
Does sweating become useless when the air is above body temperature?

So if sweat wicks away heat from our warmer body to the colder air then wouldn't that mean that if the air was above our body's temperature that sweating would make our body even hotter?
gpt
Quite the opposite. Sweat becomes more effective at higher temperatures. Sweat doesn't do much in liquid form, it's the *evaporation* of the sweat that cools us, and higher temperatures makes it evaporate more quickly. (At lower temperatures your body sheds heat through radiation and convection, but as temperatures rise sweat takes over.)

Because of *latent heat of vaporization*, when water evaporates it absorbs an enormous amount of heat - e.g., it takes 1 calorie of heat to raise 1 gram of water by 1 degree C, but it takes over 500 calories to evaporate 1 gram of water even though its temperature will only rise by another 1 degree.

Said another way, when 1 gram of water/sweat evaporates, it absorbs over 500 calories of heat. So the evaporation of sweat sucks a lot of heat off your skin.

Humidity in the air slows evaporation; the higher the humidity the slower the evaporation. In very high humidity your sweat won't evaporate much at all so you get drenched in sweat. High humidity and high temperatures can be very dangerous because your body can't cool itself.

Apparently humans can survive in zero-humidity air up to 70 degrees C (158 F) as long as they stay hydrated, but running out of water would quickly be fatal.

On the other hand, wind/airflow increases evaporation, so even if the air is hotter than your body wind actually helps you stay cool as long as you are able to sweat and the humidity isn't too high.