The Basics

You can find a hair dryer like this one in almost any drug or discount store. This model has two switches, one to turn it on and off and one to control the rate of airflow. Some models have an extra switch that also lets you regulate the temperature of the airflow.


A basic hairdryer

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.

Hair dryers were first sold in the 1920s. Since then, thousands of patents have been issued for different hair dryer designs, but most of them only tweak the outside packaging of the hairdryer so that it looks more aesthetically appealing to you. Aside from the addition of some safety features, the inside of a hair dryer hasn't changed too much over the years.

A hair dryer needs only two parts to generate the blast of hot air that dries your hair:

  • a simple motor-driven fan
  • a heating coil


Inside a hair dryer.
Motor-driven fan (left) and heating element (right).

Hair dryers use the motor-driven fan and the heating coil to transform electric energy into convective heat. The whole mechanism is really simple:

  1. When you plug in the hair dryer and turn the switch to "on," current flows through the hair dryer.
  2. The circuit first supplies power to the bare, coiled wire of the heating element, which becomes hot.
  3. The current then makes the small electric motor spin, which turns the fan.
  4. The airflow generated by the fan is directed down the barrel of the hairdryer, over and through the heating element.
  5. As the air flows over and through the heated coil, heat rising from the coil warms the air by forced convection.
  6. The hot air streams out the end of the barrel.