Cortex
Definition
The middle, and largest, layer of the hair shaft. It contains cortical cells, pigment granules (melanin), and cortical fusi (air spaces). The distribution, density, and clumping of pigment granules are among the features compared between questioned and reference hairs.
- Position
- Middle layer of the hair shaft, between cuticle and medulla
- Size
- Largest of the three hair layers
- Contents
- Cortical cells, pigment granules (melanin), cortical fusi
- Forensic use
- Pigment distribution and density compared between questioned and reference hairs
Common questions
Why is the cortex the most informative layer for microscopic hair comparison?+
It holds most of the pigment and the structural features that vary between individuals, such as granule size, density, and clumping pattern, whereas the cuticle mainly shows scale pattern and the medulla shows a simpler air-space structure, giving the cortex the richest set of comparison points.
Can cortex features alone individualise a hair to one person?+
No. Microscopic hair comparison, including cortex features, can support or exclude a common source but is not considered individualising on its own; nuclear or mitochondrial DNA from the hair, when recoverable, is needed for a statistically supported identification.
What is cortical fusi and why does it matter in comparison?+
Cortical fusi are small air-filled spaces within the cortex, often concentrated near the root; their presence, size, and distribution add another variable examiners note alongside pigment pattern when comparing questioned and known hair samples.
Related terms
- Cuticle
- The waxy, polymer layer covering the outer surface of leaf epidermal cells. It protects against water loss and herbivory but, forensically, it...
- Medulla
- The central canal of the hair shaft, which may be continuous, interrupted, fragmented, or absent. Medullary pattern and the medullary index (medulla...
- Follicular Tag
- Translucent sheath tissue adhering to the root of a forcibly pulled hair. Contains nucleated epithelial cells from the inner root sheath and...
- Medullary Index
- The ratio of the medulla diameter to the total hair shaft diameter. In companion animal hair identification, a medullary index above 0.5...
- Anagen
- The active growth phase of the hair cycle, lasting two to six years in scalp hair. During anagen the root matrix is...
- Anagen / Catagen / Telogen
- Hair growth phases. Anagen is the active growing phase (about 85 percent of scalp hairs), catagen the brief transition, telogen the resting...
- Cortical Fusi
- Air-filled spaces within the cortex of the hair shaft, most common near the root end. Their size, shape, and distribution are minor...
- Mitochondrial DNA (mtDNA)
- DNA located in mitochondria rather than the cell nucleus. Present in hundreds to thousands of copies per cell, making it recoverable from...
- Natural Fibre
- Fibre of biological or mineral origin. Animal (wool, silk, cashmere, mohair, alpaca), vegetable (cotton, jute, flax, hemp, sisal, coir) or mineral (asbestos;...
- Synthetic Fibre
- Fibre manufactured from regenerated cellulose (rayon, acetate) or polymer chemistry (nylon, polyester, acrylic, polypropylene, spandex, kevlar). Identified by birefringence, FTIR and pyrolysis...
- Telogen
- The resting phase of the hair cycle, lasting two to four months in scalp hair. The root forms a club-shaped, non-pigmented bulb....
Explained in these topics
- Hair Anatomy and the Growth CycleThe middle and bulk layer of the hair shaft, composed of elongated keratin fibres and melanin pigment granules. Pigment distribution, density, and granule morp...
- Hair and Fibers: Nature, Types, Structure and ExaminationMiddle, thickest hair layer of spindle-shaped cortical cells. Holds pigment granules, cortical fusi (air spaces) and ovoid bodies. Source of colour, texture an...
- Hair Examination and Microscopy