Final answer:
Overlapping hair color on previously tinted hair can cause breakage and a visible line of demarcation.
Step-by-step explanation:
Overlapping hair color on previously tinted hair can cause breakage and a visible line of demarcation.
When hair is tinted, the dye molecules penetrate the hair shaft and bond to the hair proteins. If additional hair color is applied on top of the previously tinted hair, the overlapping can lead to excessive chemical processing that weakens the hair and causes breakage.
The visible line of demarcation occurs when the new hair color does not blend seamlessly with the previously tinted hair, resulting in an obvious difference in color between the two sections.
Learn more about hair color overlap