Which part of the hair shaft is located between previously chemically treated hair and the scalp?

The part of the hair shaft located between previously chemically treated hair and the scalp is known as new growth. This area represents the hair that has grown after a chemical treatment, such as coloring, has been applied to the rest of the hair. New growth is not affected by the prior chemical processes and typically appears as the natural hair color of the individual.

In hair coloring practices, understanding the distinction between new growth and the previously treated hair is vital for achieving an even color result, particularly when retouching roots. This helps haircolorists apply products appropriately to avoid over-processing and damage to the previously treated length of the hair.

The other options represent parts of the hair that do not fulfill this specific role. The hair ends refer to the tips of the hair, which have usually been processed multiple times, while the demarcation line indicates the distinct line where treated and untreated hair meet. The root zone encompasses both the scalp area and new growth, but it is not as specific as the term new growth itself.