A hair dryer, also called a blow dryer or hot air brush, uses an electric current to warm up water molecules in damp hair so it evaporates more quickly. The process creates temporary hydrogen bonds that strengthen shape and structure. Manufacturers design hair dryers to be lightweight and easy to handle during operation. This includes ergonomics and safety features that anticipate how users will misuse the product. Power A hair dryer generates heat by passing electric current through a metal wire that looks like a coiled spring. The wire is made of a special alloy called nichrome, which conducts electricity well but doesn’t get hot enough to burn your hair or scalp. It’s safer than copper because it’s not prone to oxidation at high temperatures. To produce a strong gust of air, the nichrome wire is attached to a small motor that begins spinning when you supply power. The motor then drives a fan that’s inside the housing to create centrifugal movement. The force of the spin draws in air from small air inlets that are covered with a grill for safety. You can adjust the force of the airflow by altering the amount of electrical current that flows through the circuit board that feeds the motor and fan. The switch you use to turn the hair dryer on and off controls the amount of current that goes to these components. Temperature Hair dryers convert electric current into heat energy by using a heating element and a motor-driven fan to blow hot air over wet hair. This accelerates the evaporation of water from the hair and allows the hair to be styled in new ways. The heating element is usually a coiled nichrome wire wrapped around mica insulating boards. Nichrome is a poor conductor of electricity, so it takes a long time for the alloy to get properly hot from the current flowing through it. However, unlike iron, nichrome does not oxidize at the temperatures used in toasters and hair dryers. To avoid overheating, most hair dryers have a safety cut-off switch that trips if the temperature rises too high. The switch is made out of a bimetallic strip, which consists of two sheets of metal that expand when heated at different rates. When one sheet of metal becomes larger than the other, it bends and trips a switch that cuts off power to the hair dryer. Airflow The airflow of a hair dryer determines how quickly your hair will dry. To generate a strong flow of hot air, the hair dryer’s motor spins a fan which blows over and through its heating element. The heat generated by the element warms the air, which then flows down the barrel of the hair dryer, through the nozzle and out the vent. Hair dryers also increase the evaporation of water in your hair’s cuticles by raising their temperature. The higher the temperature, the faster your hair will dry, since individual molecules move faster from liquid to a gas state. In order to avoid overheating, a safety sensor is built into the hair dryer that trips the power supplying switch on reaching a certain threshold. Some hair dryers have additional heat protection by utilizing a bi-metallic strip made of two metals that expand on heating. This prevents the hair dryer from getting too hot and potentially burning you. Noise Hair dryers can emit high levels of noise, which some people may find annoying or even damaging to their ears. This is why it is important to opt for models with lower decibel ratings and multiple heat and speed settings when choosing a new hair dryer. To reduce hair dryer noise, the invention uses an insulating boot that encases the motor and isolates its vibration from the rest of the housing. The upper air inlet passage is also doubled in size to increase the rate of air flow through it, further reducing its sound producing properties. Senior Beauty Lab chemist Sabina Wizemann (she/her) leads all of GH’s beauty tests, including those for hair dryers. She has over 15 years of experience in the beauty departments at Good Housekeeping, Prevention and Woman’s Day. She has a Ph.D in organic chemistry and was a research scientist at the National Institute of Health. She is a member of the American Chemical Society and is an advisory board member for the Women’s Voices for Science organization.