Forensic Science: Fundamentals & Investigations, Chapter 3 3
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
4. Today: chemical tests, neutron activation analysis, and DNA analysis
Forensic Science: Fundamentals & Investigations, Chapter 3 4
The Function of Hair
o Regulates body temperature
o Decreases friction
o Protects against sunlight
Forensic Science: Fundamentals & Investigations, Chapter 3 5
The Structure of Hair
Forensic Science: Fundamentals & Investigations, Chapter 3 6
The Structure of Hair
o A follicle embedded in the skin produces the hair shaft
o Three layers (illustrated above):
• the inner medulla
• the cortex
• the outer cuticle
Hair shape (round or oval) and texture (curly or straight) is influenced heavily by
genes. The physical appearance of hair can be affected by nutritional status and
intentional alteration (heat curling, perms, straightening, etc.).
Sources: http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair & http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric1.htm#Index%20(Hairs)
Hair is composed of the protein keratin, which is also the primary component of
finger and toe nails.
Hair is produced from a structure called the hair follicle. Humans develop hair follicles
during fetal development, and no new follicles are produced after birth.
Hair color is mostly the result of pigments, which are chemical compounds that reflect
certain wavelengths of visible light.
The body area (head, arm, leg, back, etc.) from which a hair originated can be
determined by the sample’s length, shape, size, color, and other physical
characteristics.
Biology of Hair
In order to test hair evidence for DNA, the root must be present.
Hair Structure
Hair is composed of three principal parts:
The structure of hair has been compared to that of a pencil with the
medulla being the lead, the cortex being the wood and the cuticle
being the paint on the outside.http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair
Cuticle – outer coating composed of overlapping scales
Cortex – protein-rich structure around
the medulla that contains pigment
Medulla – central core
(may be absent)
Forensic Science: Fundamentals & Investigations, Chapter 3 9
Cuticles, Cortex, and Medulla
Forensic Science: Fundamentals & Investigations, Chapter 3 10
Types of Cuticle and Cortex
o Cuticle:
• the outermost layer
• over-lapping scales that protect the inner layers
o Cortex:
• Thickest layer
• Contains most of the pigment
• Distribution of pigment varies
• Usually denser nearer the cuticle
• Made up of keratin
Characteristics of the cuticle may be important in distinguishing
between hairs of different species but are often not useful in
distinguishing between different people.
Info: http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair Image: http://www.hairdressersus.com/micro/Image5b.jpg
Hair Structure
Cuticle
The cuticle varies in:
• Its scales,How many there are per centimeter,
How much they overlap,
Their overall shape, and
How much they protrude from the surface
• Its thickness, and
• Whether or not it contains pigment.
Cortex
The cortex varies in:
• Thickness
• Texture
• Color
• Distribution of the cortex is perhaps the most important component
in determining from which individual a human hair may have come.
• Microscopic examination can also reveal the condition and shape of
the root and tip.
Info: http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair Image: http://www.extrapersonality.com/hair.html
Hair Structure
Medulla
The medulla may vary in:
• Thickness
• Continuity - one continuous structure
or broken into pieces
• Opacity - how much light is able to
pass through it
• It may also be absent in some species.
http://library.thinkquest.org/04oct/00206/lesson.htm#t_hair
Like the cuticle, the medulla can be important for
distinguishing between hairs of different species, but often
does not lend much important information to the
differentiation between hairs from different people.
Hair Structure
http://www.bfro.net/images/whatis/figures/Fig.%203%20with%20caption.jpg
Forensic Science: Fundamentals & Investigations, Chapter 3 14
Types of Medulla
Forensic Science: Fundamentals & Investigations, Chapter 3 15
Types of Hair
Buckled Blunt Double Medullao A cross section: circular, triangular, irregular,
or flattened
o Shape: influences the curl of the hair
o Texture: coarse or fine
Forensic Science: Fundamentals & Investigations, Chapter 3 16
Forensic scientists distinguish six types of hair on human body
Human hair varies on the body• Head
• Eyebrows and Lashes
• Mustache and Beard
• Underarms
• Body hair or auxiliary hair
• Pubic
• Each has its own shape and charactyeristics
Forensic Science: Fundamentals & Investigations, Chapter 3 17
The Life Cycle of Hair
Hair proceeds through 3 stages as it develops:
o Anagen stage:
• hair actively grows
• cells around the follicle rapidly divide and deposit materials in the hair
o Catagen stage:
• hair grows and changes
o Telogen stage:
• follicle becomes dormant
Forensic Science: Fundamentals & Investigations, Chapter 3 18
Treated Hair
o Bleaching
• disturbs the scales on the cuticle and
• removes pigment
• leaves hair brittle and yellowish
o Dyeing colors the cuticle and the cortex
Forensic Science: Fundamentals & Investigations, Chapter 3 19
Racial Differences
o 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
Forensic Science: Fundamentals & Investigations, Chapter 3 20
Animal Hair and Human Hair
o All mammals have hair. Its main purpose is to: regulate body temperature-to keep the body warm by insulating it.
o Pigmentation:
• animal hair is denser toward the medulla
• human hair tends to be denser toward the cuticle
o Banded Color Patterns:
• possible in animals
• not in humans
o Medulla Index: much thicker in animals
Forensic Science: Fundamentals & Investigations, Chapter 3 21
Medulla Index—Animals vs. Humans
Forensic Science: Fundamentals & Investigations, Chapter 3 22
Animal Hair and Human Hair
Spinous Coronal Imbricateo Animals: cuticle scales resemble petals
(spinous) or a stack of crowns (coronal)
o Humans: commonly flattened and narrow (imbricate)
Forensic Science: Fundamentals & Investigations, Chapter 3 23
Using Hair in an Investigation Hair is Class Evidence
o Hair can adhere to clothes, carpets and many other surfaces and be transferred to other locations. This is called: secondary transfer
o Macroscopic investigations indicate • length
• color
• curliness
o Phase contrast microscopy shows
• presence of dye or other treatments
o Electron microscopes yield yet more detail
Forensic Science: Fundamentals & Investigations, Chapter 3 24
Using Hair in an Investigation
o Note the overlapping scales and the pigment granules in the cortex
o If a hair is forcibly removed from a victim, the entire hair follicle may be present. This is called a follicular tag.
Forensic Science: Fundamentals & Investigations, Chapter 3 25
Testing for Substances in the Hair Shaft
o Chemical tests
o Since hair grows out of the skin, chemicals that the skin absorbs can become: incorporated into hair, Ingested or absorbed toxins can be detected by chemical analyses of hair. These ingested or absorbed toxins include: arsenic, drugs, lead.
o Examining a hair shaft
• timeline for exposure to toxins
o Neutron Activation Analysis (NAA)
• concentrations of substances
Forensic Science: Fundamentals & Investigations, Chapter 3 26
Testing the Hair Follicle
o Microscopic assessment
• Cost effective and quick
o pattern of the medulla.
o types of scales on the cuticle.
o pigmentation of the cortex.
o Blood test
• Determine blood type
o DNA analysis
• Identification with a high degree of confidence
Forensic Science: Fundamentals & Investigations, Chapter 3 27
Microscopic Assessment
o Preparation
Forensic Science: Fundamentals & Investigations, Chapter 3 28
. . . . . . . . . . . . . . Summary . . . .
o Hair functions to regulate temperature, reduce friction, protect from light, and produce sensory data.
o Hair consists of a (a) hair shaft produced by a (b) follicle embedded in the skin.
o The shaft consists of an outer cuticle, a cortex, and an inner medulla.
o Hair characteristics vary depending on location on the body.
Forensic Science: Fundamentals & Investigations, Chapter 3 29
. . . . . . . . . . . . . . . . . . Summary
o Hair development has three stages: anagen, catagen, and telogen.
o Various hair treatments produce characteristic effects useful to forensic experts.
o Some characteristics can be grouped into general racial categories.
o Forensic experts examine hair using chemicals, light, electrons, neutrons, and DNA sequencing.
