Many people are familiar with the daily routine of washing, drying, and styling their hair. Although hair will eventually dry on its own if given enough time, most people reach for a hair dryer to speed up the process. While science may have disproven the link between wet heads and catching colds, it's still no fun to sit around with a head full of wet hair, especially in the winter.
Hair dryers, also known as blow dryers, were first sold in the 1920s. At first they were pretty dangerous to use -- hundreds of people were electrocuted when they dropped their hair dryer into water-filled sinks and bathtubs.
The hair dryer dries your hair by speeding up the evaporation of water from the hair's surface. The hot air emitted from a hair dryer increases the temperature of the air surrounding each strand of hair. Since warm air can contain more moisture than air at room temperature, more water can move from your hair into the air. The increase in temperature also makes it easier for the individual molecules in a water droplet to overcome their attraction to one another and move from a liquid to a gas state.
via How Stuff Works