What is the main difference between semi-permanent and permanent hair color?

The distinction between semi-permanent and permanent hair color primarily revolves around longevity and durability on the hair. Semi-permanent color typically deposits color without altering the hair's natural structure, lasting anywhere from several washes to around 24 shampoos. In contrast, permanent hair color penetrates the hair shaft and creates a lasting change in color that remains until the hair grows out or is cut. This ability of permanent hair color to fully permeate the hair cuticle and provide a more enduring result is key to its longevity.

While semi-permanent options are often more forgiving and fade gradually, they do not provide the same level of coverage or lasting power as permanent dyes. Therefore, the essential difference regarding how long each type lasts is fundamental to understanding their application and suitability for various hair coloring needs.