Forensic
Science
Hair Evidence:
Microscopic Examination
Hair Shaft
Composed of:
Cuticle—outside
covering, made of
overlapping scales
Cortex—inner layer
made of keratin and
embedded with
pigment
Medulla—inside layer
running down the
center of the cortex
Medulla
The medulla is a central core of
cells that may be present in the
hair.
Types???
What type of medulla?
What type of medulla?
What type of medulla?
Medullary Index (MI)
MI = diameter of medulla
diameter of hair shaft
Diameter
 “Edge to edge” measurement
 Because this measurement is
so small, we must use RATIOS
to calculate it.
Hair Tip
 “Distal end” of the hair
 Appearance can help to
pinpoint the origin of the
hair.
Scissor Cut
Razor Cut
Broken Hair
Burned Hair
Glass-Cut or
Broken
Hair Tip
Worn RazorCut Tip
Bulb or Root
 “Proximal end” of the hair
 Appearance can help to
identify whether a violent
crime occurred.
Which was forcibly
removed?
Why the difference?
 Hair has three phases of growth:
 Anagen – primary growth of hair
 Catagen – intermediate phase
 Telogen – hair ready to be pushed out of the head.
 When hair falls out naturally, it is in the telogen
phase. Hair in the telegen phase is only loosly
attached to the follicle. The bulb appears
unstretched and no follicular tissue clings to it.
 Anagen hair is tightly bound to the follicle. When
such hair is forcibly removed, it resists the force
(causing it to stretch out). It also carries along
with it the material it was clinging to.
Hair Forensics: DNA
 Often it is not possible to
extract DNA fully, or there is not
enough tissue present to
conduct an examination.
 Hairs with large roots and
tissue are promising sources of
nuclear DNA.
Fluorescence
Term used to describe objects
that glow under certain
wavelengths of light
Fluorescence
Caused by dyes, bleaches, and
optical enhancers.
 Chemically treated hair
 Fabrics
Hair Cuticle
The cuticle is a
translucent outer layer
of the hair shaft
consisting of scales
that cover the shaft.
Cuticular scales always
point from the proximal
end of the hair to the
distal end of the hair.
Cuticle
There are three
basic scale
structures of a
cuticle:
coronal (crown-like)
spinous (petal-like)
imbricate (flattened)
To visualize a cuticle:
 Paint clear fingernail polish on a
glass slide.
 When the polish begins to dry, place
a hair on the polish.
 When it is almost dry, lift off the hair
and observe the scale imprints.
Time for you to look at
hair microscopically!!
Goal: to identify, describe, and
compare (using proper
descriptive terminology) hairs
from different sources. You will
look at different people’s hair,
hair that has been chemically
treated, and hair from different
parts of your body.