A blowdryer or hair dryer is an electromechanical device designed to blow cool or hot air over damp hair, in order to accelerate the evaporation of water particles and dry the hair. Blowdryers allow to better control the shape and style of hair, by accelerating and controlling the formation of temporary hydrogen bonds inside each strand. These hydrogen bonds are very powerful (allowing for stronger hair shaping than even 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.
Blowdryers were invented around the end of the 19th century. The first model was created by Alexander F. "Beau" Godefroy in his salon in France in 1890. The handheld, household hair-dryer first appeared in 1920. Blowdryers are used both in the beauty salon by professional stylists, and in the average household by consumers.
Most models use coils of wire that have a high electric resistivity and heat rapidly with an electric current. A fan (usually powered by a universal motor) blows ambient air past the hot coils resulting in heated air effective for drying. The heating element in most dryers is a bare, coiled nichrome wire that is wrapped around insulating mica heating boards. Nichrome wire is used in heating elements, because of two important properties: it is a poor conductor of electricity and it does not oxidize when heated.
In terms of modern models, a survey of stores in 2007 showed that most hair dryers have 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, so it takes a lot less time for the hair to dry.
Many of these dryers have “cool shot” buttons which turn off the heater and just blow room temperature air while the button is pressed. This function is useful in helping to maintain the hairstyle by setting it. The cold air also reduces frizz and can help to bolster the shine in the hair.
Many also feature “ionic” operation, to reduce the amount of static electricity build-up in the hair. Manufacturers also claim this makes the hair “smoother.” Some stylists[who?] today consider the introduction of ionic technology to be one of the most important advances in the beauty industry.
Hair dryers are available with different attachments, such as diffusers, airflow concentrators, and comb nozzle attachments. A diffuser is an attachment that is used on hair that is fine, colored, permed or naturally curly. It works by diffusing 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 exact opposite of a diffuser. It makes the end of the blowdryer more narrow and thus helps to concentrate the heat into one spot in order 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 just the dryer without a brush or comb.
Before the invention of the hair dryer, it was common for men and women to dry their hair using a vacuum cleaner. In fact, the original model of hair dryer was invented in 1890 by Alexander Godefroy by taking inspiration from the vacuum cleaner. Alexander invented it for usage in his hair salon in France and it was not portable or handheld, but instead could only be used by having the woman sit underneath it. A hair hood dryer has a hard plastic dome that comes down and fits over a person's head in order to dry their hair. Hot air is blown out through the tiny openings around the inside of the dome so the person's hair is dried evenly. Today hair hood dryers are mainly found in hair salons. However across the world today, the hair hood dryers are replaced with the manual hair dryers and is mostly used by persons who wouldn't mind spending a day in the salon due to the length of time that is being spent under the hair hood.
It was not until around 1915 that the hair dryer began to go on the market in handheld form. This was due to innovations by National Stamping and Electricworks under the white cross brand (advertised here in 1915), and later U.S. Racine Universal Motor Company and the Hamilton Beach Co. that allowed the dryer to be handheld. Even in the 1920s, the new dryers were often heavy, weighing in at approximately 2 pounds (0.91 kg), and difficult to use. They also had many instances of overheating and electrocution. It was also only capable of using 100 watts, so it took a lot longer to dry hair (the average dryer today can use up to 2000 watts of heat).
Since the 1920s, development of the hair dryer has mainly focused on improving the wattage and superficial exterior and material changes. In fact, the mechanism of the dryer has not had any significant changes since its inception. One of the more important changes for the hair dryer is having the materials change to plastic so that it is more lightweight. This really caught on in the 1960s with the introduction of better electrical motors and the improvement of plastics. Another important change happened in 1954 when GEC changed the design of the dryer to move the motor inside the casing. 
Also, including safety mechanisms in them has been important, especially since Consumer Product Safety Commission set up guidelines in the 1970s that hair dryers had to meet in order to be considered safe to manufacture. Since 1991 the CPSC has mandated by U.S. law that all dryers must use a ground fault circuit interrupter so that it cannot electrocute a person if it gets wet. By 2000, deaths by blowdryers had dropped to less than four people a year, a stark difference to the hundreds of cases of electrocution accidents during the mid-twentieth century. In terms of positive health, this type of dryer has also been cited as an effective treatment for head lice. Overall, the size, weight, noise, and appearance of the hair dryer has dramatically changed from the heavy bulky noisy contraptions of the early part of the twentieth century, to the streamlined plastic that people are used to today.
There are two other major types of blowdryers other than the handheld. These are the bonnet hair dryer and the rigid-hood dryer. The bonnet dryer was introduced to consumers in 1951. This type of dryer worked by having the dryer, usually in a small portable box, connected to a tube that went into a bonnet with holes in it that could be placed on top of a person's head. This worked by giving an even amount of heat to the whole head at once. The 1950s also saw the introduction of the rigid-hood hair dryer which is the type most frequently seen in salons, and it had a hard plastic helmet that goes over the head. This dryer works similarly to the bonnet dryer but at a much higher wattage.
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