What does a hair follicle contain that is responsible for forming hair?

A hair follicle plays a crucial role in hair growth, and its various components contribute to different aspects of hair structure. Among the options provided, one specific part of the hair follicle is essential for the actual formation of hair: the hair matrix. The hair matrix is a layer of rapidly dividing cells located at the base of the hair bulb, which is part of the hair follicle. These cells produce keratin, the primary protein that makes up hair, as well as contribute to the formation of the hair shaft.

The hair root refers to the portion of the hair that is embedded in the follicle, but it does not actively participate in the production of hair. The hair bulb is the enlarged bottom part of the hair follicle where the matrix is located, but by itself, it does not generate hair without the activity of the matrix. The hair shaft is the visible part of the hair that extends above the skin's surface, formed as a result of the keratinized cells produced in the matrix.

Given this context, the hair matrix is the correct part of the follicle responsible for forming the hair itself, as it is where the actual hair growth occurs through cellular division and keratin production.