Hydrogen peroxide is the most commonly used developer or oxidizing agent used in hair coloring products. Hydrogen perixode's pH is between 2.5 and 4.5. To become active it needs to be mixed with ammonia or other alkaline compounds to become active. In the US developers are measured by volume, such as 10 volume. In Europe developers are measured in percentages such as 3%. Volume refers to the amount of oxygen that would be removed from a peroxide solution if the molecules into components. Hydrogen peroxide is a chemical compound consisting of hydrogen and oxygen. If the oxygen were set free, hydrogen peroxide would turn to water. To prevent the oxygen from escaping it is important to immediately begin applying a color product that has been mixed with developer to the hair.