Hair serves many functional roles including thermal regulation and ultraviolet protection from the sun . Hair fiber morphology is complex and is defined by three distinct regions: the medulla, cortex, and cuticle . Found primarily in coarse hair, the medulla is located in the core of a hair fiber and is loosely packed and porous . The cortex constitutes the majority of a hair fiber's mass, up to 90%, made up of spindle-shaped cells that are aligned with the fiber long axis and contain keratin and keratin associated proteins (KAPs) . The outermost layer surrounding the cortex, termed the cuticle, provides a protective layer consisting of one or more overlapping scale-like structures forming lamellar compositions consisting of 75% heavily crosslinked proteins and 25% fatty acids named the epicuticle . A scheme representing the morphology of hair fibers can be observed in Figure .