Why do you only sweat from your head?

The body perspirates, or sweats, as a natural instinct to cool down. When water evaporates, it absorbs energy from a nearby source. On human skin, this causes the skin to feel cool as the water droplets evaporate. As our bodies heat up due to air temperature, exercise, ect., our bodies sweat. This puts liquid on the skin to be evaporated into the air, cooling us off and preventing our bodies form over-heating.
To remove heat from the body.