Where is humidity? During hot and humid weather, we sweat incessantly due to high humidity. But when we sit under a fan, we feel cold and comfortable. Why do we feel cold and chilled? Why don’t we feel the humidity?
 A: The moving air produced by the fan causes forced evaporation of  the sweat secreted by the sweat glands.  It takes energy (heat) to change sweat (liquid water) into water vapor and that heat energy is taken from the body thus cooling the body down which makes one feel more comfortable.  This is one of Nature’s way of regulating body temperature.
A: The reason you are sweating is not high humidity directly. It is high temperature. But high humidity prevents the body from cooling down and thus indirectly causes sweating. 


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*Temperature: The body starts sweating when it becomes too hot. The evaporation of sweat into the air absorbs energy, so by sweating, the body has a mechanism for cooling itself down.

*Humidity: Now, the dryer the air, the more water can evaporate into the air. In 0 % humidity with no water present in the air, the sweat evaporation is fast and cooling very effective. In 100 % humid air where the air is "stuffed" and can contain no more  water, the evaporation process stops. Then suddenly sweating doesn't work and the body cannot cool effectively anymore - which causes it to sweat even more.
When sitting under a fan, the air is constantly circulated. Convection increases. The air close to your body absorbs the sweat through evaporation, and quickly it is replaced by new air that can start a new evaporation and so on. This is the function of a ceiling fan. 
A: When you switch on the fan, the air of the fan removes or evacuates the water vapour from the nearby areas.So.the place [not large although] becomes void of water vapour...And so when you sit there with sweat, your sweat is absorbed by the apparently dry air of that place.During evaporation, the sweat absorbs the latent heat of vaporization from your body and thus you feel cold...
