Sweating before heavy rain...

Sweating, also called perspiration, is a continuous process. As the sweat glands, present below the skin, secrete sweat, it evaporated into the atmospheric air depending on the humidity (moisture content) of the air. If the air is dry (low humidity) the evaporation is fast. But, before rain, the atmospheric air is saturated with water vapour and so the evaporation of sweat slows down. As a result the sweat accumulates on the skin giving us a feeling that we sweat more.