Final answer:
The tough exterior layer of the hair that protects it from damage is known as the cuticle. This layer, along with the external root sheath, an extension of the epidermis, helps maintain the hair's integrity.
Step-by-step explanation:
The cuticle layer is the tough exterior layer of the hair. It surrounds the inner layers and protects the hair from damage. The cuticle is the outermost layer of keratinocytes originating from the hair matrix, evident in a cross-section of the hair bulb. This layer acts as a protective barrier, effectively reducing the potential for harm to the inner structure of the hair, including the cortex and medulla. The external root sheath, which is an extension of the epidermis, also plays a role in enclosing and protecting the hair root and is more keratinous in the upper regions. The comprehensive structure and composition of the hair follicle, including the cuticle and external root sheath, are vital for maintaining the integrity and health of the hair.