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
When water evaporates, heat energy is required to break the bonds between water molecules and separate the molecules from their closely packed liquid form to their distance-separated gas (vapor) form.
Now if you blow air at a wet surface, the air has some capacity to pick up water molecules, and it does so depending on wind speed and on how much water is already in the air (humidity). But the molecules of water that are “peeled off” the surface still need that heat energy to separate, so they literally suck heat out of their immediate vicinity.
Therefore, wind-evaporation sucks heat out of the water (sweat) and your body. This is called the wind chill effect, and is why we sweat. We sweat so the wind can evaporate that water off our skin and suck heat out of our bodies in the process.
Not all animals can sweat.
And how much water is picked up by the air depends on how much water may be already in the air. When it’s humid outside, the air is pretty full of water already, and won’t pick up more.
Therefore, humid hot feels much hotter to you than dry-air hot, especially if the dry-air has a wind to it. Overheating is more dangerous if the air is humid, because your body can’t use sweat to cool down.
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