Hair shaft
The visible portion of a hair that extends above the skin surface. It consists of dead, keratinized cells arranged in layers.
Hair cuticle: The outermost layer of overlapping, flattened cells covering the hair shaft. Its overlapping scales protect the shaft and influence shine and friction.
Hair follicle: A skin organ that produces and anchors a hair. The follicle builds the cells that later form the visible shaft.
Hair microscopy: The microscopic examination of hair structure, pigment, and surface features. Microscopy makes the shaft’s layers and damage patterns visible.
Hair root: The portion of a hair located within the skin and enclosed by the follicle. Unlike the visible shaft, the root remains beneath the skin.
Hair cortex: The thick middle layer of the hair shaft, made largely of keratin fibers and containing most hair pigment. This layer supplies most of the shaft’s strength, elasticity, and color.
Hair matrix: A zone of rapidly dividing cells at the base of a growing hair follicle. Matrix cells differentiate and keratinize as they move upward into the shaft.
Forensic hair analysis: The examination of hair evidence to assess its characteristics and possible associations with people or sources. Shaft features can support comparisons, though they rarely identify a person by themselves.
Hair bulb: The enlarged base of a hair root that surrounds the follicular growth region. It is a living growth structure, unlike the dead shaft above the surface.
Hair medulla: The central core of some hair shafts, often composed of loosely arranged cells and air spaces. Its presence and continuity vary across hair types and individual hairs.
Hair keratinization: The process by which developing hair cells accumulate keratin, lose their nuclei, and become hardened shaft material. It transforms living follicular cells into the dead structure above the skin.