Forensic Analysis of Hair
How useful is hair in a forensic
investigation?
• Used to back up circumstantial evidence
and help place individuals at the crime
scene.
• Hair without the follicle = class
characteristics
• Hair with the follicle = individual
characteristics (allows for DNA
fingerprinting)
Morphology of Hair
Morphology - refers to color
and structure
Hair grows out of an organ
called the hair follicle
•the root is embedded in the
follicle
•the shaft is the main part of
the hair
•the tip is at the opposite end
to the root.
Morphology of Hair
• Forensic scientists primarily examine the
hair shaft, which is composed of three
layers:
•
a. Cuticle
b. Cortex
c. Medulla
Cuticle
•Outer surface of hair
•Reason that hair resists
changes in structure and
does not easily decompose
•Formed from overlapping scales that point towards the tip
of the hair (formed from keratinized cells)
•Scales are more prominent on animal hair than human
hair and can be used to ID the species
•Examined by comparison microscope or hair casts.
Examples of Cuticles
Cortex
•Main body of hair shaft
•Contains pigment granules
and possibly air bubbles
called cortical fusi
•Color, shape and distribution of granules are analyzed by
criminalist
•Examined by placing hair on a microscope slide in a liquid
with a similar refractive index
Medulla
Central canal running through the hair (not always present)
Medullary index – diameter of the medulla relative to
diameter of entire hair (represented as a fraction)
•Humans approx. 1/3 or less
•Other animals 1/2 or more
0
1/10
1/3
1/2
9/10
Medulla Classification
Human: usually absent or fragmented
- can be continuous (Mongoloid)
Animal: usually continuous or interrupted
-many are also patterned
(ex, cat = string of pearls)
Also:
Absent
Patterned
-A database has been established
containing the 35 most common
types of animals encountered. Can
be searched by scale pattern or
medulla type
Examples of Medullas
Hair Shape
Straight
Curly
Asian/
Caucasian
Caucasian
No twist
No twist
Kinked
African
Twists and undulates
Root
Allows for hair growth
3 Stages of hair growth:
1. anagen – (up to 6 years) – follicle is actively
producing hair
- roots have a flame-shaped appearance
b/c attached to the follicle
- if the hair is pulled out at this stage,
typically will have the follicular tag attached
2. catagen – (2-3 weeks) – hair growing still but slowly
- roots have elongated appearance b/c root bulb
shrinks
3. telogen – (2-6 months) – hair pushed out of
follicle and shed
- root has a club shaped appearance
Stages of Hair Growth
Identification and Comparison of Hair:
Steps the Forensic Analyst Takes
1. Determine if hair belongs to an animal or a human
- EASY – use medulla/cuticle to ID species
2. Determine if human hair matches known samples
- HARD – morphology/color differs w/in the same
person
Things examined by the forensic
scientist
1. Compare color, length, diameter
2. Examine medulla, cuticle, cortex
– abnormal morphology can indicate disease or vitamin
deficiencies
3. Try to determine if hair is dyed or bleached
a. Dyed hair – dye reaches into the cortex and cuticle
b. Bleached hair – removes pigment so has yellow tint
Estimate time of dying possible since hair grows about
1cm/month
Common Questions
1. Can the area of the body the hair came from be determined?
2. Can racial origin, age and sex be determined?
Racial origin usually can be determined:
• African American – kinky, dense, unevenly distributed pigments
• Caucasian – straight or wavy, more evenly distributed pigments
Age and sex cannot be determined at this time
3. Can it be determined if hair was removed with force or naturally shed?
-
Typically hair removed by force or with a brush has follicle still attached
Important consideration is how quickly hair is pulled out
4. Are there any ways to individualize hair?
-
DNA technology – examining follicular tag or root when hair is in
anagen phase
Collection of Hair
1. Need an adequate number of control samples from same area of body
2. Need to try and collect full length hairs from all over scalp
3. Entire hair length should be collected since may change in color and
morphology
4. During an autopsy it is now routine to remove hair samples in case they are
needed later on.
Case Story
Recap of Analytical Techniques
Comparison microscope
Physical Properties
Temperature (melting point/freezing point)
Weight/Mass
Density
Refractive Index
Chemical Properties
Color tests
Microcrystalline tests
Chromatography
Spectrophotometry
Mass Spectrometry
Objectives
1. Learn the morphology and distinguishing features of hair
2. Compare various different types of hair under a microscope.
3. Analyze the medulla, cortex and cuticle of several hair samples.
4. Describe the hairs of several species of animals.
5. Describe the collection procedures for hair.