Human hair is a protein filament that grows from follicles in the skin. It is primarily made of a protein called keratin, which is also found in nails and the outer layer of skin. Hair serves various functions, including protection, regulation of body temperature, and sensory perception. The structure of human hair consists of three main layers: the cuticle, the cortex, and the medulla. The cuticle is the outer layer that protects the inner layers, while the cortex provides strength and color. The medulla, which is present in some hair types, is the innermost layer and may play a role in hair texture.