Hair color cream (hair dye, hair tint, hair toner) is used for hair coloring. Hair coloring is the practice of changing the color of hair. The main reasons for this practice are cosmetic (e.g., to cover gray hair, to change to a color regarded as more fashionable or desirable, or to restore the original hair color after it has been discolored by hairdressing processes or sun bleaching). Hair coloring can be done professionally by a hairdresser or independently at home.
The four most common classifications are permanent, demi-permanent (sometimes called deposit only), semi-permanent, and temporary.
Permanent hair color generally contains ammonia and must be mixed with a developer or oxidizing agent in order to permanently change hair color. Ammonia, in permanent hair color is used to open the cuticle layer so that the developer and color molecules together penetrate into the cortex. The developer or oxidizing agent, comes in various volumes. The higher the developer volume, the higher the lift will be of a person’s natural hair pigment. Someone with dark hair wishing to achieve two or three shades lighter may need a higher developer, whereas someone with lighter hair wishing to achieve darker hair will not need a high developer. Timing may vary with permanent hair coloring but is typically 30 minutes or 45 minutes for those wishing to achieve maximum gray coverage.
Demi-permanent hair color is hair color that contains an alkaline agent other than ammonia (e.g. ethanolamine, sodium carbonate) and, while always employed with a developer, the concentration of hydrogen peroxide in that developer may be lower than used with a permanent hair color.
Semi-permanent hair color has smaller molecules than temporary dyes. These dyes only partially penetrate the hair shaft. For this reason, the color will survive repeated washing, typically 4–5 shampoos or a few weeks. Semi-permanents contain no, or very low levels of developer, peroxide or ammonia, and are therefore safer for damaged or fragile hair.
Temporary hair color is available in various forms including rinses, shampoos, gels, sprays, and foams. Temporary hair color is typically brighter and more vibrant than semi-permanent and permanent hair color.