Wisconsin Cosmetology Practice Exam 2024 - Free Cosmetology Practice Questions and Study Guide

The other options are incorrect because the medulla, cuticle, and follicle do not chemically change the hair. The medulla is the innermost layer of the hair and is mainly composed of air spaces, while the cuticle is the protective outer layer made up of overlapping scales. The follicle, on the other hand, is the structure in the skin from which the hair grows. The cortex, located between the medulla and cuticle, is the main structural component of the hair and is responsible for its shape, strength, and color. It contains important proteins and pigments that can undergo chemical changes through processes such as perming or coloring. Therefore, all chemical changes take place in the cortex of the hair.