A hairdryer is an electromechanical device that blows ambient or hot air over damp hair to speed the evaporation of water to dry the hair.

Blow dryers enable better control over the shape and style of hair, by accelerating and controlling the formation of temporary hydrogen bonds within each strand. These bonds are powerful (allowing stronger hair shaping than the sulfur bonds formed by permanent waving products) but are temporary and extremely vulnerable to humidity. They disappear with a single washing of the hair. Hairstyles using blow dryers usually have volume and discipline, which can be further improved with styling products, hairbrushes, and combs during drying to add tension, hold and lift. Blow dryers were invented in the late 19th century. The first, stationary, model was created by Alexander F. Godefroy in France.

Most hair dryers consist of electric heating coils and a fan (usually powered by a universal motor). The heating element in most dryers is a bare, coiled nichrome wire that is wrapped around mica insulators. Nichrome is used because of two important properties: It is a poor conductor of electricity and it does not oxidize when heated. A survey of stores in 2007 showed that most hair dryers had ceramic heating elements (like ceramic heaters) because of their “instant heat” capability. This means that it takes less time for the dryers to heat up and for the hair to dry. Many of these dryers have “normal mode” buttons that turn off the heater and blow room-temperature air while the button is pressed.

This function helps to maintain the hairstyle by setting it. The colder air reduces frizz and can help to promote shine in the hair. Many feature “ionic” operation, to reduce the build-up of static electricity in the hair, though the efficacy of ionic technology is of some debate. Manufacturers claim this makes the hair “smoother”. Some stylists consider the introduction of ionic technology to be one of the most important advances in the beauty industry. Hairdryers are available with attachments, such as diffusers, airflow concentrators, and comb nozzles.

  • A diffuser is an attachment that is used on hair that is fine, colored, permed, or naturally curly. It diffuses the jet of air so that the hair is not blown around while it dries. The hair dries more slowly, at a cooler temperature, and with less physical disturbance. This makes it so that the hair is less likely to frizz and it gives the hair more volume.
  • An airflow concentrator does the opposite of a diffuser. It makes the end of the blow dryer narrower and thus helps to concentrate the heat into one spot to make it dry rapidly.
  • The comb nozzle attachment is the same as the airflow concentrator, but it ends with comb-like teeth so that the user can dry the hair using the dryer without a brush or comb.

Hairdryers have been cited as an effective treatment for head lice and earwax prevention.