Why do we sweat order to cool off?

Question

Drops of water and ethanol are placed on an overhead projector and the ethanol drop is seen to evaporate more rapidly.

Our bodies utilize sweating as a means to stay cool and maintain body temperature. Sweat is primarily water. Why does sweating cool us of, would it have been better for nature to have evolved to use ethanol instead of water as the primary component of sweat? Why or why not?

Answer 1

Sweat cools us off because evaporation requires energy. To move from a liquid phase (on your skin) to a vapor phase (in the air), the water in your sweat needs some energy input. This energy comes from your skin, which in turn lowers your surface temperature.

Ethanol has a higher vapor pressure than water (mostly due to the lesser extent of hydrogen bonding), so it will evaporate faster than water. However, because ethanol experiences less hydrogen bonding than water, it also requires slightly less energy to evaporate. This means that it would take more ethanol to get the same cooling effect.

So, it would not necessarily be more efficient for humans to sweat ethanol, we would just have to sweat more of it to compensate for the lower heat of vaporization. To know for sure, you could estimate the rate of evaporation for both water and ethanol, and multiply by the heat of vaporization of each.