Why is humidity so exhausting?

Further, sweat evaporates from the surface of skin, pulling heat away in the process. In high humidity, though, when the air around is already full of moisture, sweat is slower to evaporate and can't cool us down as well. ... If that goes on for too long, and fluids go unreplenished, heat exhaustion can set in.

How does humidity affect the body?

When the air has a high moisture content, as is the case in humid weather, this sweat cannot evaporate, leaving our bodies feeling hot and sticky. To cool off, our bodies must work even harder. This results in excessive sweating, increased rate and depth of blood circulation and increased respiration.