Why is it essential to avoid overlapping color on previously colored hair?

Avoiding the overlap of color on previously colored hair is essential primarily because it can cause uneven results and damage. When color is applied to hair that has already been treated, there is a risk that the previously colored sections will absorb the new color differently than the uncolored hair. This can result in patchy coloration, where some areas may appear darker or more vibrant than others.

Additionally, overlapping color can lead to excessive processing of the hair. Each time a hair strand is exposed to hair dye or lightener, it undergoes a chemical reaction. Reapplying color to already colored hair can lead to an accumulation of chemical exposure, which can weaken the hair structure, leading to breakage and other forms of damage. By avoiding overlap, you ensure a more uniform color result and maintain the integrity and health of the hair.