Hair Analysis

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Hair Analysis

• Forensic Science

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Hair Analysis

• Human hair is one of the most frequently found
  pieces of physical evidence located at the scene
  of a crime and can provide a link between the
  criminal and their act.

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Did You Know?

• Chaetophobia is the fear of hair.
• Tonsurphobia is the fear of haircuts.

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Did You Know?

• An average human scalp contains 100,000 hairs and
  most people lose between 25 and 125 hairs a day.

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Did You Know?

• Hair generally grows at a rate of approximately
  3/16 per day, or approximately ½ per month.

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Did You Know?

• Hair is naturally colored by pigment granules
  (melanin) in the cortex whereas dyed hair has
  melanin in the cuticle as well as the cortex.

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• Properties of hair that make it useful to
  criminalists

• small
• easily shed
• clings to clothing and other materials

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• Properties of hair that make it useful to
  criminalists

• goes unnoticed by perpetrators at crime scenes
• survives for a long period of time even years
  after bodies decompose

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• How hair (and fiber) evidence is useful to
  criminalists

1. Helping to establish the scope of the crime
   scene
2. Placing a perpetrator at a scene
3. Connecting a suspect with a weapon

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• How hair (and fiber) evidence is useful to
  criminalists

4. Supporting witness statements 5. Connecting
crime scene areas (abduction, vehicle used, dump
site)
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• How hair (and fiber) evidence is useful to
  criminalists

Examiners can find many toxins, particularly
heavy metals like arsenic, in hair. Also, if the
follicle is attached to the hair, examiners can
often extract DNA and use it to make an exact
match.
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• Hair Differences

Hair varies not only from person to person but
also from one area of an individuals body to
another the hair on your head is different from
the hair on your arms or other parts of your body
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• External Hair Anatomy

Hair grows out of the skin from a pocket of
specialized cells called a follicle.
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• Hair Follicle

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Biology of Hair
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.
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Biology of Hair
Hair color is mostly the result of pigments,
which are chemical compounds that reflect certain
wavelengths of visible light.
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.).
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Biology of Hair
The body area (head, arm, leg, back, etc.) from
which a hair originated can be determined by the
samples length, shape, size, color, and other
physical characteristics.
In order to test hair evidence for DNA, the root
must be present.
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• Stages of Hair Development

Anagen growing Catagen at rest Telogen dying
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• Two Parts of Hair

The shaft of the hair projects from the skin, and
the root lies below the epidermis.
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• Hair Root

The root of a mature human hair is similar in
appearance to a flower bulb.
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• External Part of Hair

The root end is called the proximal end and the
growing tip end is called the distal end.
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• Hair Shaft

The shaft of the hair is made up of three parts
cortex, cuticle, and medulla.
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Hair Structure
Cuticle outer coating composed of overlapping
scales
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.
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• Hair Cuticle

The cuticle is a layer of cells that cover the
surface of the shaft and look like scales on a
fish or perhaps even roofing tiles.
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• Hair Cuticle

Scales overlap and always point up the shaft,
away from the bulb.
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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.

Characteristics of the cuticle may be important
in distinguishing between hairs of different
species but are often not useful in
distinguishing between different people.
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• Types of Cuticles

Coronal (crown like) scales   Spinous (petal
like) scales Imbricate (flattened) scales
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• Coronal Cuticle(crown like)

give the hair a mosaic surface appearance. Human
hair rarely has these scales, but theyre common
among rodents
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• Spinous Cuticle(petal like)

tend to be somewhat triangular in shape. These
scales arent found in humans but are typical of
cats.
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• Imbricate Cuticle(flattened)

scales are found in humans and many other
animals.
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• Imbricate Cuticle(human)

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• Different Types of Cuticles

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Hair Structure

• 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.

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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.

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• Medulla of Hair

The central core of the hair, the medulla
contains a collection of cells but appears as if
its an empty or mud-filled central canal.
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• Medullas Appearance

1. Fragmented (trace)
2. Intermittent (discontinuous)
3. Continuous

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• Basic Structure of the Medulla

Uniserial(Rabbit)
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• Basic Structure of the Medulla

Multiserial(Rabbit)
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• Basic Structure of the Medulla

Vacuolated (dog)
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• Basic Structure of the Medulla

Lattice(deer)
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• Basic Structure of the Medulla

Amorphous(human)
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• Checklist of Comparisons

• Color and width
• Distribution pattern of the medulla
• Color and distribution pattern of pigment in the
  cortex
• Cuticle pattern

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• Hair Root of a Cat

The frayed end is character-istic of a cat root.
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• Hair of a Cat

The uniserial or lader like medulla in this slide
is also that of a cat.
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• Hair of a Rabbit

This multiserialmedulla composed of many ladders
is characteristic of hair from a rabbit.
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• Hair of a Seal

The spinous scale pattern of seal hair is easily
observable without preparing a scale cast.
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• Hair of a Human

The human scale pattern is not as easily
observable under a whole mount. This scale cast
enhances the pattern.
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• Hair of a Human

This club-shaped human root is characteristic of
dead or dying root in telognic stage.
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• Plucked Hair

A human hair that has been forcibly removed will
have a root that looks like this. Part of the
follicle will be attached.
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• Cut Hair

A hair that has been freshly cut with scissors
will look like this. Notice the ragged edge and
sharp corners.
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• Cut Hair

A hair with rounded corners indicates that the
hair has not been freshly cut.
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• Dyed Hair

This hair has been dyed. Notice the even color
distribution cross section of the hair.
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• Dyed Hair

The demarcation line is observable on the same
hair between the dyed and undyed portions. The
length of undyed portions can be used to
determine how long ago the hair was dyed.
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• Hair

Some hairs are not round, but kidney shaped in
cross section. The overlapping can be deduced
from a longitudinal mount, as shown in this slide.
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• A Louse

External environment also can play a role in hair
examinations. This picture reveals the outline
of a louse.