Demi-permanents have several advantages as compared with permanent color. Because there is essentially no lifting (i.e., removal) of natural hair color, the final color is less uniform/homogeneous than a permanent and therefore more natural looking; they are gentler on hair and therefore safer, especially for damaged hair; and they wash out over time (typically 20 to 28 shampoos), so root regrowth is less noticeable and if a change of color is desired, it is easier to achieve. Demi-permanent hair colors are not permanent but the darker shades in particular may persist longer than indicated on the packet.
Semi-permanent hair dye
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. However, semi-permanents may still contain the possibly carcinogenic compound p-phynylinediamine or other such ingredients.
Temporary hair color
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. It is most often used to color hair for special occasions such as costume parties and Halloween.
The pigment molecules in temporary hair color are large and cannot penetrate the cuticle layer. The color particles remain absorbed (closely adherent) to the hair shaft and are easily removed with a single shampooing. Temporary hair color can persist on hair that is excessively dry or damaged in a way that allows for migration of the pigment to the interior of the hair shaft.
Alternative hair color
Alternative hair coloring products are designed to create hair colors not typically found in nature. The available colors are diverse. For example, the colors green and fuchsia.
Permanent alternatives in some colors are available from big haircare brands. Some alternative color shades are blacklight-reactive, to show up under nightclub lighting.
The chemical formulae of alternative color dyes typically contain only tint and have no developer. This means that they will only create the bright color of the packet if they are applied to light blond hair. People with darker hair (medium brown to black) need to use a bleaching kit before tint application. Some people with fair hair may benefit from prior bleaching as well. Gold, yellow and orange undertones in hair that has not been lightened enough can adversely affect results, especially with pinks, blues and greens. Although some alternative colors are semi-permanent, such as blue and purple, it could take several months to fully wash the color from bleached or pre-lightened hair.