All related- Why does lower temperatures and higher humidy feel so hot? Is overheating when hiking as dangerous or more likely in no humidity or high? How does sweating help cool you down?
In: Biology
At any temperature, water wants to be at an equilibrium with its environment. If you take a closed container of water, it will evaporate until the amount of water in the air above it can’t absorb any more. But getting water to evaporate takes energy, which also cools the water slightly. This process is called “evaporative cooling.”
So what happens when you sweat is that the sweat on your body evaporates due to your body heat, and this evaporating water removes the heat from your body, cooling you. But what happens if there is already a lot of water vapor in the air (high humidity)? In this situation, your sweat doesn’t evaporate as quickly since the air already has too much water vapor in it. If the humidity is high enough, this can make it impossible to lose heat be evaporative cooling. This is why a “dry” heat feels less harsh than a muggy heat. In a dry heat evaporative cooling is very effective.
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