Answer
Some of the water molecules from the perspiration have enough kinetic energy to escape the surface of the perspiration. This lowers the average kinetic energy of the perspiration which lowers the temperature of the remaining perspiration which in turn lowers the temperature of your body.
Work Step by Step
Some of the water molecules from the perspiration have enough kinetic energy to escape the surface of the perspiration. This lowers the average kinetic energy of the perspiration which lowers the temperature of the remaining perspiration which in turn lowers the temperature of your body.