What distinguishes semi-permanent color from demi-permanent color?

Semi-permanent color is distinguished from demi-permanent color primarily by its formulation and characteristics related to lightening hair. Semi-permanent hair color contains smaller pigment molecules that do not penetrate the hair shaft deeply; instead, they coat the outside of the hair cuticle. This means that semi-permanent color does not contain ammonia or peroxide, which are necessary to lighten the hair. Therefore, it cannot lighten the hair color from its natural shade or any previous color.

Demi-permanent color, on the other hand, typically includes a low volume of developer (usually containing peroxide), which can slightly lift the hair's natural pigment, allowing for a point of contrast. While demi-permanent colors generally last longer than semi-permanent ones due to their capacity to penetrate the hair structure more effectively, the most defining characteristic of semi-permanent color is its inability to lighten hair. This note clearly demonstrates the essential distinction in their chemical behavior concerning lifting or lightening capabilities.