Hair is a filamentous appendage composed primarily of keratin, a tough fibrous structural protein. Its growth originates from a specialized structure called the follicle, which is rooted in the dermis of the skin. The lifecycle of hair growth is cyclical, transitioning through distinct phases: the active anagen phase, the regression catagen phase, and the resting telogen phase. From a biological standpoint, the hair shaft provides various functions, including protection and insulation, while its properties—such as color, texture, and diameter—are determined by various biochemical processes during formation. The structure is highly durable and exhibits anisotropic properties due to the arrangement of its keratin layers.