What does the hair shaft contain?

The hair shaft is primarily composed of keratin, a fibrous structural protein that is a key component of hair, nails, and the outer layer of skin. This protein gives hair its strength, elasticity, and durability. The majority of the hair shaft is made up of three layers: the cuticle (outermost), the cortex (the middle layer), and the medulla (innermost), all of which contain keratin.

While it is true that the hair shaft is made up of dead cells, this does not encompass the full context of what the hair shaft is, as the question specifically asks about the key component of the shaft itself. The living portion of hair is located within the hair follicle, where new hair cells are produced. Therefore, saying that the hair shaft contains the living part of hair is inaccurate. Similarly, hair follicle cells are related to hair growth and production but are not a part of the hair shaft itself. Thus, keratin protein stands out as the defining substance that constitutes the hair shaft.