Chapter 3
THE STUDY OF HAIR
Sept. 3, 2013
Trichology
The scientific study of the structure, function, and
diseases of human hair.
Very valuable in Forensic Science
More resistant to decay
Remains intact much longer
Class Evidence
Material that connects an individual or thing to a
certain group.
Cannot be used to identify a specific individual
Can identify a group or class that share similar hair
type.
Secondary Transfer
Pet hair
Analyzing Hair
Physical Characteristics: Broad racial background
Chemical Characteristics: Drug use and other toxins,
heavy metals, nutritional deficiencies.
Follicle present, potential to recover DNA
Individual Evidence
A kind of evidence that identifies a particular person
or thing
DNA
Fingerprint
Trace Evidence: small but measureable amounts of
physical or biological material found at a crime scene.
Comparison Microscope
A compound microscope
that allows the side-by-side
comparison of samples, such
as hair or fibers
Today!
Neutron activation analysis
and DNA fingerprinting
and is considered a
standard tool in trace
evidence analysis.
Function of Hair
All mammals have hair.
Regulate body temperature
Decrease friction
Protect against sunlight
Sense Organ
Very dense Hair=Fur
Hair
Temperature Regulation
Hair and muscles work together to
regulate body temp.
Muscles pull hair upright, creating
pockets that trap air
Muscles relax and hair flattens against
the body, releasing trapped air
Humans are born with about 5 million
hair follicles, only 2% of which are on
the head.
As humans age, hair density decreases
Structure of Hair
Follicle
The actively growing root or
base of a hair containing
DNA and living cells
Papilla
Network of blood vessels that
supply nutrients to feed the
hair and help it grow.
Sebaceous gland (bulb)
Secretes oil to help the hair
conditioned
Erector muscle causes the
hair to stand up
Structure of the Hair
Shaft
Composed of the protein
Keratin;
a type of fibrous protein that
makes up the majority of the
cortex of a hair.
Makes hair both strong and
flexible
• Inner Medulla, Cortex, and
Outer Cuticle
•
Pencil
Hair
The Cuticle
Transparent tough outer layer of the hair composed of
overlapping scales.
The Cortex
The region of a hair located outside of the medulla
containing granules of pigment (melanin) which gives the hair
its color.
The Medulla
The center of the hair, can be hollow or filled with cells.
Classify hair into 5 different groups depending on the
appearance of the medulla.
Hair Classification
 See Figure 3-6 on page 53
Continuous: one unbroken line of color
Interrupted: Pigmented line broken at regular intervals
Fragmented: Pigmented line unevenly spaced
Solid: Pigmented area filling both the medulla and the
cortex
None: No separate pigmentation in the medulla
Types of Hair
Hair can vary in so many ways!
Cross section view
Textures
Color
Not all hairs on a person’s head are exactly
the same
Sample of 50 from head
Sample of 25 from pubic region
Hair in Different Regions of
the Body
6 Types on Human Body
Head Hair
Eyebrow and Eyelashes
Beard and Mustache
Underarm Hair
Auxiliary or Body Hair
Pubic Hair
Body Hair
Distinguished by their
Cross-sectional Shape
Head- circular or elliptical
Eyebrow/eyelashes- also
circular, but have tapered
ends
Beard- thick and triangular
Body hair- oval or triangular
(depending on shaved often
or not)
Pubic- oval or triangular
Life Cycle of Hair
3 Stages of Development
 Anagen Stage: lasts approximately 1,000 days. Period of
active growth when the cells around the follicle are
rapidly dividing and depositing materials with in the
hair.
 Catagen Stage: next stage as hair grows ad changes.
 Telogen Stage: final stage, the follicle is dormant or
resting and hairs are easily lost.
Hair
 Racial Differences (page 55)
 Animal Hair and Human Hair (page
55)
 Hair in an investigation
 Microscopy
Substances in Hair
Drug Tests
Timeline
1.3 cm per month (.44 mm per day)
9 cm = approximately 7 months
NAA (Neutron Activation Analysis)
14 different elements in a single 2cm
long strand
DNA
Follicular tag