BleachBleach removes hair color by chemically reacting with the melanin in the hair. During the reaction, the bleach molecule oxidizes the melanin molecule, meaning the melanin is present but either is colorless or has a small pale yellow tint. Some blond or gold color may remain depending on how much phaeomelanin was in the hair, because bleach reacts better with eumelanin than phaeomelanin. Hydrogen peroxide is often used for bleaching hair. Hydrogen peroxide is put into an alkaline solution, which opens up the hair shaft so the peroxide is able to react with the melanin. Hair needs to be bleached to a pale yellow in order to dye the hair because that means most of the melanin has been decolorized. Depending on the color of one's hair, one might have to go through multiple stages of bleaching so all the melanin molecules react.12
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Permanent Hair ColorFirst, the original color of the hair has to be removed in order to deposit the permanent hair dye, so ammonia or an other bleaching agent is used to remove the natural hair color. Ammonia is often mixed with peroxide and acts as a catalyst, and the existing hair color is removed when the mixture breaks the chemical bonds of the hair color, which releases sulfur in the process. Ammonia causes the cuticles of the hair shaft to swell, which makes it easier for the permanent dye to be let in. After bleaching, the new color is bonded to the cortex in the inside of the hair shaft, and is sealed in with conditioners.13
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Hair Dye ColorsOne of the main chemicals used in hair dye is paraphenylenediamine (PPD). It creates a brown color, and has been used in hair dye for 150 years. To create other colors, couplers are added to the hair dye mixture. Couplers are chemical compounds that are not colored but they react with the molecules of the main chemicals in hair dye to create a different shade. There are three colors of couplers: blue, red, and green. Usually, hair colorists will use a mix of couplers to get the desired hair color.14
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