Hair Analysis
Forensic Science 1

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

Did You Know?
Hair is naturally colored by pigment granules
(melanin) in the cortex whereas dyed hair has melanin in the cuticle as well

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 varies not only from person to person but also from one area of an individual’s 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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Hair grows out of the skin from a pocket of specialized cells called a 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.

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.).

Biology of Hair
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.
In order to test hair evidence for DNA, the root must be present.

Stages of Hair Development:
Anagen: growing
Catagen: at rest
Telogen: dying
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The the
the hair projects from the skin, and
below the of lies epidermis.
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The root of a mature human hair is similar in appearance to a flower bulb.
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The root end is called the
end and the growing tip end is called the
end.

The shaft of the hair is made up of three parts: cortex, cuticle, and medulla.
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Cuticle
– outer coating composed of overlapping scales
Cortex
– protein-rich structure around the medulla that contains pigment
Medulla
– central core
(may be absent)
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.

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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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 .

Coronal (crown like) scales
Spinous (petal like) scales
Imbricate
(flattened) scales
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give the hair a mosaic surface appearance.
Human hair rarely has these scales, but they’re common

tend to be somewhat triangular in shape. These scales aren’t found in humans but are typical of cats.
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scales are found in humans and many other animals.
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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 .

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.
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 .

The central core of the hair, the medulla contains a collection of cells but appears as if it’s an empty or mud-filled central canal.
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1. Fragmented (trace)
2. Intermittent (discontinuous)
3. Continuous
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Basic Structure of the Medulla
(Rabbit)
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Basic Structure of the Medulla
(Rabbit)
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Basic Structure of the Medulla
(dog)
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Basic Structure of the Medulla
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Basic Structure of the Medulla
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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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The uniserial or lader like medulla in this slide is also that of a cat.
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This multiserial medulla composed of many ladders is characteristic of hair from a rabbit.
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The spinous scale pattern of seal hair is easily observable without preparing a scale cast.
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The human scale pattern is not as easily observable under a whole mount. This scale cast enhances the pattern.
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This club-shaped human root is characteristic of dead or dying root in telognic stage.
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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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A hair that has been freshly cut with scissors will look like this.
Notice the ragged edge and sharp corners.
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A hair with rounded corners indicates that the hair has not been freshly cut.
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This hair has been dyed.
Notice the even color distribution cross section of the hair.
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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
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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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External environment also can play a role in hair examinations.
This picture reveals the outline of a louse.
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