Demi permanent hair color can last up to 6 weeks and typically fades after 20 to 28 hair shampoo washes. As a hair-coloring agent, demi permanent formulas are used to enhance natural hair color, to darken the natural hair shade and to refresh previously colored hair.
Unlike semi-permanent and permanent hair-coloring agents, demi permanent hair-coloring formulas do not contain ammonia and contain a significantly less amount of hydrogen peroxide. While still employed as the developer in the formula, the amount of hydrogen peroxide contained in demi permanent formulas is not enough to lighten the hair. This means that demi permanents cause less damage to the hair.
Because demi permanent formulas have little or no lightening effect on the hair, it cannot be used to color hair lighter. Demi permanent formulas are commonly used and are better suited for glazing, refreshing previously dyed hair and correcting hair coloring mistakes.
Demi permanent hair coloring does a better job at covering gray hair than semi-permanent formulas. Because demi permanent formulas do not lift or bleach the hair, they give the hair a more natural looking shade. Demi permanent formulas also take less commitment because they wash out a few weeks after the application.