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Chapter 3 The Study of Hair
By the end of this chapter you will be able to:
Identify the various parts of a hair
o Describe variations in the structure of the
medulla, cortex, and cuticle
o Distinguish between human and nonhuman
hair
o https://www.youtube.com/watch?v=3JjevVi1yc
U
o
All Rights Reserved South-Western / Cengage Learning © 2012, 2009
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Forensic Science: Fundamentals & Investigations, Chapter 3
Chapter 3 The Study of Hair
By the end of this chapter you will be able to:
o
o
o
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Determine if two examples of hair are from
the same person
Explain how hair can be used in a forensic
investigation
Calculate the medullary index for a hair
Forensic Science: Fundamentals & Investigations, Chapter 3
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History of Hair Analysis
1. 1883: Alfred Swaine Taylor and Thomas
Stevenson covered hair in a forensic science
text
2. 1910: Victor Balthazard and Marcelle Lambert
published a comprehensive study of hair
3. 1934: Dr. Sydney Smith, analyzed hairs side
by side using a comparison microscope
4. Today: chemical tests, neutron activation
analysis, and DNA analysis
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Forensic Science: Fundamentals & Investigations, Chapter 3
Hair
o Hair is considered what type of evidence?
• Individual and Class; why?
• Only with the root (follicle) can it be
classified to an individual (DNA)
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What Can Hair Tell Us?
o
o
o
o
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Broad racial background
Drugs and other toxins
Presence of heavy metals
Nutritional deficiencies
Forensic Science: Fundamentals & Investigations, Chapter 3
The Function of Hair
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o
Regulates body temperature
o
Decreases friction
o
Protects against sunlight
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The Structure of Hair
o
o
A follicle embedded in the skin produces the
hair shaft
Three layers (illustrated above):
•
•
•
*
*
the inner medulla
the cortex
the outer cuticle
Forensic Science: Fundamentals & Investigations, Chapter 3
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Caucasoid
o
Oriental
o
Negroid
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The Structure of Hair
Hair is composed
of a protein called
keratin, the same
protein that
makes up horns,
hooves, beaks
and feathers
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Forensic Science: Fundamentals & Investigations, Chapter 3
Cuticles, Cortex, and Medulla
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Types of Cuticle
and Cortex
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Cuticle:
•
•
o
Cortex:
•
•
•
•
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the outermost layer
over-lapping scales that protect the inner layers
Thickest layer
Contains most of the pigment
Distribution of pigment varies
Usually denser nearer the cuticle
Forensic Science: Fundamentals & Investigations, Chapter 3
Types of Medulla
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Types of Hair
Buckled
o
o
o
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Blunt
Double Medulla
A cross section: circular, triangular, irregular,
or flattened
Shape: influences the curl of the hair
Texture: coarse or fine
Forensic Science: Fundamentals & Investigations, Chapter 3
Types of Hair
Human hair varies on the body
•
•
•
•
•
•
•
•
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Head
Eyebrows
Lashes
Mustache
Beard
Underarms
Body hair
Pubic
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The Life Cycle of Hair
Hair proceeds through 3 stages as it develops:
Anagen stage:
o
•
•
o
Catagen stage:
•
o
hair grows and changes
Telogen stage:
•
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hair actively grows
cells around the follicle rapidly divide and
deposit materials in the hair
follicle becomes dormant
Forensic Science: Fundamentals & Investigations, Chapter 3
Treated Hair
o
Bleaching
•
•
•
o
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disturbs the scales on the cuticle and
removes pigment
leaves hair brittle and yellowish
Dyeing colors the cuticle and the cortex
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Racial
Differences
Broad, racial groups do exhibit some shared
physical characteristics
o But NOT applicable to all individuals in these
groups
Therefore,
o Individual hairs CANNOT be assigned to any
of these groups
o
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Forensic Science: Fundamentals & Investigations, Chapter 3
Animal Hair
and Human Hair
o
Pigmentation:
• animal hair is denser toward the medulla
• human hair tends to be denser toward the cuticle
o
Banded Color Patterns:
•
•
o
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possible in animals
not in humans
Medulla: much thicker in animals
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Medulla Index—
Animals vs. Humans
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Forensic Science: Fundamentals & Investigations, Chapter 3
Animal Hair
and Human Hair
Spinous
o
o
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Coronal
Imbricate
Animals: cuticle scales resemble petals
(spinous) or a stack of crowns (coronal)
Humans: commonly flattened and narrow
(imbricate)
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Using Hair in an
Investigation
o
Macroscopic investigations indicate
•
•
•
o
Phase contrast microscopy shows
•
o
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length
color
curliness
presence of dye or other treatments
Electron microscopes yield yet more detail
Forensic Science: Fundamentals & Investigations, Chapter 3
Using Hair in an Investigation
Note the overlapping scales and the pigment
granules (Melanin) in the cortex
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Testing for Substances
in the Hair Shaft
o
Chemical tests
•
o
Examining a hair shaft
•
o
timeline for exposure to toxins
Neutron Activation Analysis (NAA)
•
*
presence of various substances
concentrations of substances
Forensic Science: Fundamentals & Investigations, Chapter 3
Testing the Hair Follicle
o
Microscopic assessment
•
o
Blood test
•
o
Determine blood type
DNA analysis
•
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Cost effective and quick
Identification with a high degree of confidence
Forensic Science: Fundamentals & Investigations, Chapter 3
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Microscopic Assessment
o
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Preparation
Forensic Science: Fundamentals & Investigations, Chapter 3
. . . . . . . . . . . . . . Summary . . . .
o
o
o
o
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Hair functions to regulate temperature, reduce
friction, protect from light, and produce sensory
data.
Hair consists of a (a) hair shaft produced by a
(b) follicle embedded in the skin.
The shaft consists of an outer cuticle, a cortex,
and an inner medulla.
Hair characteristics vary depending on location
on the body.
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. . . . . . . . . . . . . . . . . . Summary
o
o
o
o
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Hair development has three stages: anagen,
catagen, and telogen.
Various hair treatments produce characteristic
effects useful to forensic experts.
Some characteristics can be grouped into
general racial categories.
Forensic experts examine hair using
chemicals, light, electrons, neutrons, and DNA
sequencing.
Forensic Science: Fundamentals & Investigations, Chapter 3
Hair Facts
o Hair grows slightly faster in warm weather, because heat stimulates
circulation and encourages hair growth.
o All hair is dead, with the exception of the hair that’s still inside the
epidermis of your scalp.
o Hair contains information about everything that has ever been in your
bloodstream, including drugs, and is one of the most commonly used
types of forensic evidence
o The only thing about you that can’t be identified by your hair is your
gender—men’s hair and women’s hair are identical in structure
o Black is the most common hair color. Red is the rarest and only exists
in about 1 percent of the world’s population, with blonde hair found in
2 percent.
o As soon as a hair is plucked from its follicle, a new one begins to
grow.
o Hair can grow anywhere on the human body with the exception of
the palms of hands, soles of feet, eyelids, lips, and mucous
membranes.
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Hair Facts
o Goosebumps from cold or fear are the result of hair follicles
contracting, causing the hair and surrounding skin to bunch up.
o The average number of hair strands varies by natural color, with
blondes having the most and redheads having the fewest.
o At any given time, 90 percent of the hairs in your scalp are growing,
while the other 10 percent are resting.
o Balding only begins to become visible once you’ve lost over 50
percent of the hairs from your scalp.
o A single hair has a lifespan of about five years.
o Eighty percent of Americans wash their hair twice a day.
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