Which layer of hair is the outermost one?

The outermost layer of hair is the cuticle. This layer is composed of overlapping, scale-like cells that protect the inner layers of the hair shaft, including the cortex and the medulla. The cuticle plays a crucial role in maintaining the hair's integrity, as it acts as a barrier against environmental damage, such as heat and chemical exposure. The condition of the cuticle can significantly affect the hair's appearance and texture, influencing how light reflects off the hair and contributing to its overall shine. In terms of hair care, ensuring the cuticle remains healthy is essential for the aesthetic quality of hair.

The medulla, cortex, and papilla are all important structures within the hair anatomy but are located beneath the cuticle. The medulla is the innermost layer and is often soft and spongy; the cortex is the thickest layer, containing the majority of the hair's pigment and strength; while the papilla is a structure at the base of the hair follicle that supplies nutrients for hair growth. These layers play vital roles in hair health and functionality, but they do not serve as the outermost protective barrier.