In my video titled, My Trip to Sally's Beauty Supply: A mini Haul," I explained the difference between permanent hair dye, semi-permanent hair dye, and temporary hair dye. For those of you who are still a little confused about what the differences are between them, I have outlined the characteristics of each one below.
Temporary Hair Dye: Temporary hair dye, which does not penetrate through to the cuticle layer of the hair, is incapable of altering one's hair color dramatically. Instead, it simply coats the hair shaft, giving it a sheer color that can be washed out in one or two shampooings.
Semi-permanent Hair Dye: Similar to temporary hair color, semi-permanent hair color doesn't penetrate the hair shaft and is therefore incapable of altering the color. However, if used with heat, it can partially penetrate the hair shaft. In general, semi-permanent dye coats the hair and can jazz up previously colored hair. This type of effect can last approximately six to eight weeks, depending on how often the hair is shampooed. This type of hair color does not contain any ammonia, and is therefore safer to use on relaxed and or damaged hair than permanent hair color.
Permanent Hair Dye: Permanent hair color penetrates the hair shaft and can lift one's natural shade in order to impart a new one. Permanent hair color contains peroxide, which can be damaging to relaxed hair. It is however the most effective colorant for grey hair. Permanent hair dye is the most difficult process of all the dying processes to maintain, for you have to touch up the color as your hair grows out, and use special shampoos and conditioners to prevent the new color from fading. Since it is permanent, it is also harder to get rid of. You have to either strip the color from the hair (this depends on what shade you use), or recolor the hair to return it back to its original shade. If you're going to use permanent color on relaxed hair, it should only be used as a highlight.