If you think of hair coloring on a scale of permanent to temporary, demi-permanent hair dye would fall somewhere in the middle. Demi-permanent hair dye is a coloring agent used to color the hair — more permanent than semi-permanent, or temporary, hair color, but less damaging than permanent color. There are many reasons why a hair stylist may recommend demi-permanent hair dye, but the biggest advantage is its minimally damaging effects.

Like permanent hair dye, demi-permanent hair dye contains an alkaline activating agent, but unlike permanent dye, it does not contain ammonia. Demi-permanent hair color can add both color and shine, but does not actually lighten the hair. However, unlike temporary hair dye, which does not penetrate the hair shaft but rather only coats it, demi-permanent hair dye does deposit some penetrating color to the hair shaft that can last up to 25 shampoos.

The primary use of demi-permanent hair color in a salon setting is to refresh existing color, blend gray, and provide a color boost to otherwise chemically treated or damaged hair. For people with existing color-treated hair, demi-permanent hair color can refresh the existing color without additional damage while only the new growth is retreated with the permanent counterpart. Demi-permanent hair dye is also a good choice for people who want a color boost lasting longer than temporary dye, but without the commitment of permanent dye.

Due to the absence of ammonia, demi-permanent hair dye is much gentler on the hair than the permanent variety. For this reason, many demi-permanent dyes can be used on newly relaxed or permed hair without the risk of further chemical damage. Sometimes color is applied only to give a bit of texture to the hair shaft or add shine and some demi-permanent hair dyes are even colorless in order to achieve this result.

For people wanting to lighten their hair, even a shade or two, demi-permanent hair dye is not a viable option. Alternatives to demi-permanent hair dye that will lighten the hair and may still create minimal damage, such as low-ammonia cream hair colors, are available, but any product that will lighten hair will still cause some damage, especially if the hair was previously chemically or heat damaged. Demi and semi-permanent are good choices for people who want to experiment with subtle color changes or blending gray and are the best choice for do-it-yourself hair coloring.