1. Hair
Class Evidence

2. Hair Structure and Locard Exchange
The average human body has 5 million hairs
Hairs continuously shed and are renewed at a rate of 100/day
Color
Strands on head
Blond
120,000
Brown/Black
100,000
Red
80,000

3. Hair Structure
Made up of complex protein polymers-resistant to breakage
Grows from a tube-like organ in the under layer of skin (dermis) called a hair follicle
The hair’s root is embedded in the follicle. The follicle is linked to the body’s blood supply
Important from drug and poison analysis

4. Shaft-extends out through the outer-most layer of the skin (epidermis)
Cuticle
Formed by overlapping scales that always point toward the tip end of each hair
Humans have a finer pattern of scales than animals
Important feature for species identification, not individualization
Can study the cuticle by making a cast of its surface

5. Shaft
Cortex
Made up of keratin molecules aligned parallel to the length of the hair shaft
Contains pigment that gives hair its color
Absence of pigment leaves hair white or gray
Cortical fusi-little sacs of air that come in different sizes and shapes (class characteristic)

6. Shaft Medulla Rows of cells running along the center of the cortex
May appear dark or translucent depending on whether there is air, liquid, or pigment within it
Can be continuous, interrupted, fragmented, or absent

7. Shaft
Medulla
Presence and appearance of the medulla varies among hairs of a given individual
Humans usually exhibit no medulla or have fragmented ones
Exception-Native Americans and Asian (mongoloid) race has continuous medulla
Animals usually show a wide variety of medullar patterns (species identification)
Medullary index measures the diameter of the medulla relative to the diameter of the hair shaft (expressed as fraction)
Humans – index is less than 1/3
Animals – index is ½ or greater

8. Root: Anagen Stage Lasts up to 6 years
Root attached to follicle for continued growth giving the root bulb a flame-shaped appearance
When pulled from the root, some anagen hairs will be found with a follicular tag (allows for DNA analysis)

9. Root: Catagen and Telogen Phase
Catagen Phase
Lasts 2-3 weeks
Grows at decreased rate
Root has elongated appearance as root bulb shrinks in size and is being pushed out of hair follicle
Telogen Phase
Lasts 2-6 months
Root has club-shaped appearance
Hair will be pushed out of a follicle and naturally shed

10. Identification and comparison of hair
Prime purpose for examination of hair:
Determine if the hair is human or animal
Determine whether human hair at a crime scene compares with suspect hair (difficult)
Evidential value of the comparison will depend on the degree of probability with which the examiner can associate the hair in question to a particular individual
Criminalists will looks at the color, length, and diameter of the medulla, and color intensity of pigment granules

11. Identification and Comparison of Hair
Dyed and colored hair:
Dyed color will be present in the cuticle as well as the cortex
Bleaching removes color and gives hair a yellowish tint
Can estimate time since dying or bleaching: hair grows 1 cm/month

12. Identification and Comparison of Hair
Shaft can be round, oval, or crescent shaped
Other features used: morphological abnormalities, fungal, and nit infections
11% of the hairs (9/80) in which the FBI examiners found a positive microscope match between were found to be non-matches when they were subjected to DNA analysis