Why is a neutralizing or acid-balanced step often used after a strongly alkaline service like a chemical relaxer?

A strongly alkaline service such as a chemical relaxer raises the hair's pH and swells/opens the cuticle to restructure the hair. Afterward, a neutralizing or acid-balanced step (for example, an acid-balanced shampoo) is used to bring the hair's pH back down toward its natural slightly acidic range (4.5–5.5), stop the chemical action, and help the cuticle close. Skipping this step can leave hair damaged and over-processed. Understanding pH and neutralization in chemical services is emphasized in the exam's chemistry content.