“A hand-held fan is an implement used to induce an airflow for the purpose of cooling or refreshing oneself. Any broad, flat surface waved back-and-forth will create a small airflow and therefore can be considered a rudimentary fan.
The movement of a hand-held fan provides cooling by increasing the airflow over the skin which in turn increases the evaporation rate of sweat droplets on the skin. This evaporation has a cooling effect due to the latent heat of evaporation of water. Fans are convenient to carry around, especially folding fans.”
via The Metropolitan Museum of Art