New York State Cosmetology Practice Exam 2025 - Free Cosmetology Practice Questions and Study Guide

During hair lightening, the chemical reaction that takes place is oxidation. This process involves the removal of electrons from the hair's melanin pigment, which is responsible for its color. When an oxidation agent, such as hydrogen peroxide, is applied to the hair, it reacts with the melanin-based pigments. The oxidation breaks down these pigments, resulting in a lighter color.

The reason oxidation is the key process here lies in its ability to effectively alter the chemical structure of the molecules present in the hair, specifically those that contribute to its pigmentation. As the melanin is oxidized, it fades, leading to the lightening effect associated with coloring processes.

To provide context, other reactions such as reduction, acidification, and neutralization do not specifically apply to hair lightening. Reduction typically involves gaining electrons and does not play a significant role in the color change during this treatment. Acidification refers to the process of making a solution more acidic, while neutralization deals with balancing acids and bases. These processes are not relevant to the mechanism through which hair lightening takes place. Thus, oxidation is the primary reaction responsible for effectively lightening hair color.