Hair color developer is used in conjunction with permanent hair coloring dyes, or as a stand-alone application. The most common developer used in hair coloring agents is hydrogen peroxide. The purpose of the developer is to open the hair cuticle, which allows the hair to absorb and disperse the color throughout the strand. The strength of the developer is known as the volume level, and comes in three different oxidizing strengths: 10, 20 and 30.
Adding water to the color developer before application reduces the strength of the hair colorant. This method of strength reduction is used when coloring previously dyed or colored hair. While water reduces the developing strength, it does not prevent the developer from working. Reducing the volume strength is done to prevent the chemicals within the developer from burning the scalp or over processing previously dyed hair.
Adding water to hair color developer is a necessary part of the application process for many hair-coloring agents. Water makes the developer reactive with the hair follicles. As a result, hair coloring dyes and developers that are applied to the hair are generally moistened with warm water and worked throughout the ends of the hair for about 3 minutes before rinsing out the developer. Working the developer throughout the ends of the hair prevents having uneven patches of color throughout the hair.
Some hair developers come in a powder form and must be mixed with water in a cup before being applied to the hair. The brand and volume strength of this type of developer determines how much water is necessary. For best results, follow the manufacturer's directions on how much water is required for the developer to work, according to the product promise.
While several types of hair coloring include developer as an ingredient, the Food and Drug Administration warns against the dangers of using developers more frequently than suggested by the manufacturer and hair coloring products that contain cancer causing chemicals such as 2-nitro-p-phenylenediamine and 4-amino-2-nitrophenol. To prevent adverse skin reactions to hair developers, the Food and Drug Administration suggests performing a hair strand test before processing the entire head of hair.