Follicular Tag
Definition
Translucent sheath tissue adhering to the root of a forcibly pulled hair. Contains nucleated epithelial cells from the inner root sheath and provides nuclear DNA for STR profiling. Absent on passively shed telogen hairs.
- Location
- Root of a forcibly pulled hair
- Composition
- Translucent sheath tissue with nucleated epithelial cells
- Value
- Source of nuclear DNA for STR profiling
- Absent on
- Passively shed telogen hairs
Common questions
Why does hair growth phase matter for whether STR profiling is possible?+
Only hairs pulled out with force during the anagen or catagen phase retain a follicular tag with nucleated cells; naturally shed telogen hairs lack this tissue, so examiners typically fall back to mitochondrial DNA testing on shed hairs instead.
What does the presence of a follicular tag suggest about how a hair was recovered?+
It indicates the hair was forcibly removed rather than shed naturally, which can be relevant to reconstructing events such as a struggle, in addition to enabling the higher-discrimination nuclear DNA test.
Related terms
- Cortex
- The middle, and largest, layer of the hair shaft. It contains cortical cells, pigment granules (melanin), and cortical fusi (air spaces). The...
- 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...
- 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...
- 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...
- 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 Cycle
- Hair and Fibers: Nature, Types, Structure and ExaminationSheath of epithelial tissue adhering to a forcibly pulled hair root. Presence indicates forcible removal and provides nuclear DNA. Naturally shed telogen hairs...