Dear Tom,
Why does wet skin always feel cold but dry skin doesn’t?
James Lynn, Chicago

Dear James,

The chill you feel on wet skin is due to evaporation. What we refer to as “temperature” is actually a measure of the average vibrational energy contained in the molecules of a substance. We perceive this molecular vibration as the sensation of heat. When a liquid like water changes state from a liquid to a gas its molecules vibrate more rapidly, and its temperature rises. The heat required for water to obtain enough energy for molecules to evaporate is absorbed from its environment. Consequently, evaporation is a cooling process. When water in contact with your skin evaporates heat is absorbed from your skin producing a cooling effect.