Hair
Hair
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Hair
Objective: SWBAT identify the various parts of a hair. SWBAT describe the
variations in the structure of the medulla, cortex and cuticle.
Do Now:
1. How are the layers of hair similar to the layers of a pencil
2. How can hair be used in a forensic investigation
*If students are talking during Do Now – pop quiz (click here)
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Hair
Introduction
From hair, one can determine:
If the source is human or animal
Race (sometimes)
Origin of the location on the source’s body
Whether the hair was forcibly removed
If the hair has been treated with chemicals
If drugs (or poisons) have been ingested
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Hair
Form and Structure of Hair
‡ Morphology – form and structure of
hair
‡ Average human body has about 5
million hairs
‡ Blondes average 120,000 strands of hair
on their head
‡ Redheads have about 80,000
‡ Black and brown hair people have about
100,000
‡ Hairs are continuously shed and
renewed at a rate of about 100 each
24-hour period from the scalp alone!
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Hair
Hair Shaft
Composed of:
Cuticle— clear outside covering
of hair shaft, made of
overlapping scales (pattern is
used to determine species)
Cortex—inner layer made of
keratin and embedded with
pigment; also contains air sacs
called cortical fusi
Medulla—inside layer running
down the center of the cortex
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Hair
The Cuticle
The cuticle is the outermost layer of hair which is covered with scales.
animals and are named based on their appearance. The three basic
patterns are:
Coronal- mouse
Spinous- cat
Imbricate- human
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Hair
The Cortex
The cortex gives the hair its shape.
Melanin—give hair its color
Contains keratin – a tough protein
makes hair so resistant to chemical and biological degradation.
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Hair
The Medulla
‡ Hair Core
‡ Most humans have no medulla or one that is fragmented (except
Native Americans and Asians, where medulla is usually
continuous)
Types:
Intermittent or interrupted
Fragmented
Continuous
Stacked
Absent—not present
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Hair
Human Medulla
Human medulla may be continuous,
fragmented, or absent.
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Hair
Hair Classification Activity
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Hair
Exit Ticket
1. What are the three parts of
the hair?
2. Can the hair cuticle get you
to an individual person? Why or
why not?
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Hair
Medullary Index
Determined by measuring the diameter
of the medulla and dividing it by the
diameter of the hair.
mouse
Medullary index for human hair
is generally less than 1/3.
For animal hair, it is usually
greater than 1/2.
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Hair
Hair Shape and Cross Section
Can be straight, curly, or kinky, depending on the cross-section,
which may be round, oval, or crescent-shaped.
Round
(Straight)
Oval
(Curly)
Crescent moon
(Kinky)
Human hair ranges in diameter from 25-125 µm
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Hair
Racial Characteristics of Hair
‡ Risky, but generally…
‡ Asians & Native Americans – round cross section with no twisting
‡ American & European whites, Mexicans, and people of Middle Eastern
background – oval cross section, rarely with a twist or undulation.
‡ African heritage – flat to crescent-shaped cross section with twist,
undulation and dense, clumped pigmentation.
Undulation – (in hair morphology) slight waviness
Undulated
Twisted
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Hair
Hair Growth
Terminology
Anagen—hair is actively growing; lasts up to 5 years; includes 8090% of hair follicles
Catagen—hair is not growing; a resting phase
Telogen—follicle is getting ready to push the hair out; lasts
two to six months; about 8-10% of hair follicles
Grows about 0.4 mm per day, or 1 cm per month; approximately onehalf inch per month
Replaced about every 3-5 years with new hair
Coarser hairs grow at slower rate and fall out less frequently
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Hair
The Root
Human roots look different based on whether they have been
forcibly removed or they are telogen hairs and have fallen out.
Animal roots vary, but in general have a spear shape.
Fallen out
Forcibly removed
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Hair
The Tip
Tip of mature hair will taper to a point
Recently cut hair is squared off at the tip, but within 2-3 weeks
the tip becomes rounded
Frayed hair tip results from over-processing (bleach, coloring,
straighteners, blow dryer) or age
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Hair
Hair Comparison
Color
Scale types
Length
Presence or absence of
medulla
Diameter
Distribution, shape, and color
intensity of pigment granules
• Dyed hair has color in
cuticle and cortex
Medullary type
Medullary pattern
Medullary index
• Bleaching removes pigment
and gives a yellow tint
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Hair
DNA from Hair
The root contains nuclear DNA. If the hair has been forcibly
removed, some follicular tissue containing DNA may be attached.
The hair shaft contains abundant mitochondrial DNA, inherited only
from the mother. It can be typed by comparing relatives if no DNA
from the body is available. This process is more difficult and more
costly than using nuclear DNA.
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Hair
Collection of Hair
Questioned hairs must be accompanied by an adequate number of
control samples.
• From victim
• From possible suspects
• From others who may have deposited hair at the scene
Control sample
• 50 full-length hairs from all areas of scalp
• 24 full-length pubic hairs
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Hair
Hair Toxicology
Advantages:
• Easy to collect and store
• Is externally available
• Can provide information on the individual’s history of drug use or
evidence of poisoning
Collections must be taken from different locations on the body
to get an accurate timeline.
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Hair
Hair as Chemical Indicator
‡ Metabolite – a specific product of a substance,
formed by chemical processes in the body
‡ Drugs and their metabolites, vitamins and poisons
can be detected with just a few mm of hair.
‡ Provides back up to urine and blood testing
‡ Drug metabolites only detectable in urine for approx.
3-5 days from last use.
‡ Hair grows at approx. 1 cm per month and will record
drug use over a longer period of time.
‡ Can establish dietary deficiencies and diseases
‡ Oils on scalp can deposit onto hair and will leave
evidence of environment
‡
‡
Smoke from crack cocaine can be deposited this
way
May provide a false positive
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Hair
Hair Toxicology, continued
Napoleon died in exile in 1821. By
analyzing his hair, some investigators
suggest he was poisoned by the
deliberate administration of arsenic;
others suggest that it was vapors
from the dyes in the wallpaper that
killed him.
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Hair
More about Hair
For additional information about hair and other trace evidence, check out
truTV’s Crime Library at:
www.crimelibrary.com/criminal_mind/forensics/trace/1.html
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