Where is the relaxer placed for a retouch using sodium hydroxide?

For a retouch using sodium hydroxide, the relaxer is placed only on the new growth. This method is essential because the purpose of a retouch is to relax the new, unprocessed hair that has emerged since the last chemical treatment. Applying the relaxer solely on the new growth helps to avoid over-processing the previously relaxed hair, which can lead to damage or breakage.

Putting the relaxer throughout the entire hair length, including the previously relaxed areas, could result in unwanted damage and weaken those sections of hair. Similarly, applying it on both the ends and the scalp evenly or only on the previously relaxed areas could compromise the integrity and health of the hair, as it may not provide effective results and could lead to inconsistent texture due to overexposure to the chemical in specific areas.