Hair: morphology, microscopy, morphometry; Biochemistry of hair; Transfer of hair; nDNA and mDNA in hair; Age, sex and race determination using hair; Databases of hair evidence

1. HAIR EXAMINATION

2. Forensic Significance
 One of the most often recovered types of evidence
 Hairs make good forensic evidence because they are
sturdy and can survive for many years
 they carry a lot of biological information and they
are easy and cost-effective to examine.
 DNA can also be extracted from hairs, and this adds
to their forensic utility.
 Nonhuman or animal hairs are also potentially
useful evidence, given the number of domestic
animals kept as pets
HUMAN HAIR WITH EPITHELIUM CELLS AT ROOT
ANIMAL HAIR

3. Source: Houck 2015
 Hairs are a particular structure common only to
mammals; they are the fibrous growths that originate
from their skin epidermis.
 The follicle is the structure within which hairs grow; it is a
roughly cylindrical tube with a larger pit at the bottom.
Hairs grow from the base of the follicle upward.
 In the base of the follicle, the hair is still very soft; as the
hair proceeds up the follicle, it slowly begins to harden
and dry out.
 Hair is made of keratin, a tough protein-based material
from which hair, nails, and horns are made in animals.
 The hardening process of hair growth is therefore called
keratinization.
 The follicle contains other structures, such as blood
vessels, nerves, and sebaceous glands, the latter
producing oils that coat hairs, helping to keep them soft
and pliable.
 Hairs even have muscles, called pili arrector muscles

4.  In the anagen, or actively growing, phase, the
follicle produces new cells and pushes them up the
hair shaft as they become incorporated into the
structure of the hair.
 Melanocytes Specialized cells in the follicle
produce small colored granules, called melanin (a
dark brown pigment called eumelanin and a lighter
pigment called pheomelanin)..
 After the active growth phase, the hair transitions
into a resting phase; this transitional phase is
called the catagen phase. the follicle begins to shut
down production of cells, the cells begin to shrink,
and the root condenses into a bulb-shaped
structure called a root bulb or a club root.
 The telogen phase is the resting phase for the
follicle. Cell production has ceased completely;
 When this mechanical connection breaks (through
combing, brushing, or normal wear), the follicle is
triggered into the anagen phase again and the
cycle renews.
80–90% in the anagen phase, about 2% in the catagen phase,
and about 10–18% in the telogen phase
Source: Houck 2015

5. SOURCE: FBI ARCHIVES

6. MICROANATOMY
Source: Houck 2015
The root (located proximal ) is that
portion that formerly was in the
follicle, The shaft is the main portion
of the hair. The tip is the distal most
portion of the hair.
Internally. The three main
structural elements in a hair
are the cuticle (a series of
overlapping layers of scales),
the cortex ( Fusiforms cells,
pigment granules, cortical
fusi), and the medulla.

10. General Descriptions of
Human Body Area Hair Traits
Area Diameter Shaft Tip
Head Even Straight or curly some
waviness; may be very
long
Usually cut
Pubic Varies Buckling; sometimes
extreme waviness or curl
Usually pointed
may be razor cut
Facial Wide; even Triangular in cross
section some shouldering
Usually cut; may
be scissors or
razor cut
Chest Even to some
variation
Wavy to curly; some
more straight
Usually pointed
Axillary Even; some variation Less wavy/curly than
chest
Usually pointed;
may be colorless
Limb Fine; tapering Slight arc Usually pointed
Eyebrow
/eyelash
Tapering Arc; short Pointed

11. SOURCE: FBI ARCHIVES
Color treatment hair

12. Ancestry Diameter
(μm)
Cross
Section
Pigment
Distributio
n
Cuticle Undulation
African 60–90 Flat Dense;
clumped
Thin Prevalent
European 70–100 Oval Even Medium Uncommon
Asian 90–120 Round Dense to
very dense
Thick Never
SOURCE: FBI ARCHIVES

13. Age and Sex
 The hairs of infants, for example, are generally finer
and less distinctive in microscopic appearance.
 As individuals age, hair can undergo pigment loss
and changes in the configuration of the hair shaft to
become much finer and more variable in diameter.
 Although the sex of an individual is difficult to determine
from microscopic examination, longer, treated hairs
are more frequently encountered in female
individuals.
 Sex can be determined from a forcibly removed hair
(with tissue), but this is not routinely done. Definitive
determination of sex can be accomplished through the
staining of sex chromatin in the cells found in the
follicular tissue
 nuclear DNA and mitochondrial DNA (mtDNA) tests
will provide more specific information regarding the
possible origin of the hair.