Keratin plays a crucial role in the hair structure as it provides strength and structure. It is a fibrous protein that serves as the main structural component of hair, making up the majority of its composition. This protein contributes to the hair's resilience and durability, allowing it to withstand various stresses such as styling, environmental exposure, and physical manipulation. The presence of keratin also aids in protecting the inner layers of the hair from damage.
While other choices mention helpful attributes, such as coloring, moisturizing, and heat protection, these roles are not the primary function of keratin. Color in hair is primarily due to melanin, a different pigment, while moisturization involves other substances like oils and conditioners. Heat protection can be aided by various hair products designed for styling, but it is not a function of the keratin itself. Thus, the role of keratin as a source of strength and structure is foundational for overall hair health and integrity.