1. Fiber Evidence Hair
Notes 4.1

2. Hair Evidence
The presence of hair can associate a suspect to a victim or a suspect/victim to a crime scene. It is a common way to close the linkage triangle.
The types, condition and number of hairs found all impact on their value as evidence in a criminal investigation.

3. Hair Evidence What can be determined?
Whether the hair originated from a human, an animal, or is synthetic.
If animal, it is possible to link it to a particular type of animal.
Hairs can identify species, it is not possible to identify hairs to a specific individual.
An example of this occurs when dog hairs can be associated to a particular breed but cannot be identified to a specific dog within that breed.

4. What other information can be gleaned from Hair?
If you have the follicular tag, DNA
From spectroscopy, the chemical make-up (e.g., diet, poisons, drugs)
Species
Body region
Race
Chemical treatments (dyes, bleaching, etc.)
Recently cut hair vs. worn hair

5. What is Hair?
Slender outgrowths of the skin of mammals (and only mammals)
Evolved from the scales of Reptiles!
Composed primarily of the protein keratin
Each species possesses hair with characteristic
length,
color,
shape,
scale pattern,
root appearance, and
internal microscopic features.

6. What is Hair? Hairs grow out of pits in the skin called follicles.
The base of the hair, sunk in the skin, is called the root
the part that emerges from the skin is the shaft.
The sebaceous glands secrete an oily substance, which lubricates the hair, waterproofs and conditions it.

7. What is Hair? The Hair shaft is made up of three layers Cuticle Cortex
Medulla

8. Layer 1: The Cuticle The outermost layer
A transparent, scale-like layer of overlapping cells (can you see the direction of growth?)
The protective barrier for the cortex and the medulla. 

9. Layer 2: The Cortex
composed of fibrous protein core of elongated cells
contains melanin pigment
responsible for giving the hair its strength, elasticity and resistance to change. 
Makes up about 90 percent of the total weight of the hair.
This is the layer of the hair where chemical changes take place when changing the color, waving, or relaxing the hair.

10. Layer 3: The Medulla
The center portion of the hair shaft is also called the pith
Composed of round cells, two to five rows across
Thick or coarse hair usually contains a medulla.
Fine hair for the most part lacks a medulla, as does naturally blonde hair.

11. Hair Color Melanin pigment that gives color to the hair and skin.
two types of melanin
Eumelanin is brown/black in color and is the most common type of melanin. This form of melanin gives color to hair shades from black to brown.
Phaeomelanin is red in color and gives the yellow, ginger and red shades of hair their color.
produced by cells in the cortex called melanocytes.
collect and bundle pigment proteins into melanosomes.
The size, type and distribution of melanosomes determine the color of the hair.
What determines the hue we see is the ratio of eumelanin to phaeomelanin.

12. 3 Phases of Hair Growth
Hair follicles undergo a cyclical growth pattern passing through 3 stages:
Anagen - the growth phase
Catagen – intermediate phase
Telogen - the resting phase
microscopic characteristics can determine the phase of growth of the hair.

13. Phase #1: Anagen actively growing
materials are deposited into the shaft by cells in the follicle.
actively dividing cells around the follicle grow upward to form the major components of the shaft and accompanying root sheath.
Has intact blood supply
                                               
An anagen hair that has been plucked out: notice the soft, sticky tail

14. Phase #2: Catagen Shortest phase of hair growth
Is a transition phase between the actively growing anagen and non-growing telogen
An anagen hair that has been plucked out: notice the soft, sticky tail

15. Phase #3: Telogen dormant or resting
the hair is attached to the follicle only by the root
a minimal amount of force (such as that from combing) is required to dislodge the hairs
                       
                      
A normal telogen hair with a hard 'club' end, seen under (top) a light microscope and (bottom) an electron microscope

16. Hair Growth Facts
On a Healthy Head:
80 to 90 percent of the hair follicles are in the anagen phase
2 percent are in the catagen phase
10 to 18 percent are in the telogen phase.
Which phase takes the longest? Shortest?
The average period of growth for scalp hair is approximately 1,000 days
The average scalp has between 100, ,000 follicles
The hair of men grows faster than that of woman
Hair grows faster at night and during the summer