1. Hairs
Forensic Science

2. Human Hair Is Class Evidence
Asian
African
European

3. Human Hair As Class Evidence
Can often determine body area of origin
Can determine shed vs. forcibly removed
Can often determine racial origin
Race
Diameter
Cross Section
Pigment
Cuticle
Undulation
(waviness)
African
69-90 um
Flat
Dense, clumped
Prevalent
European um
Oval
Evenly distributed
Medium
Uncommon
Asian um
Round
Dense Auburn
Thick
Never

4. Hairs are continuously shed
We lose about 100 hairs every 24 hours
Hair grows at a rate of 1 cm per month
Hair is replaced every 3-5 years with new hair
Course hairs grow at a slower rate and fall out less frequently than finer hairs do.

5. Morphology of Hair (form and structure)
Hair is made up of polymers (complex cross linked proteins)
Grows out of the dermis in follicles
Because the follicle is linked to the blood supply, hair can be analyzed for drugs and poisons.

6. Hair Structure Hair is composed of three principal parts:
Cuticle – clear outer coating composed of overlapping scales
Cortex – protein-rich (keratin) structure around the medulla that contains pigment (no pigment makes gray and white hair)
Medulla – central core (may be continuous, interrupted or in pieces/fragmented)

7. Cuticle Structure The scales point toward the tip of the hair
Coronal Spinous Imbricate
mouse
cat
human

8. 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.
Info: Image:

9. 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.
Info: Image:

10. Medulla Patterns Medullary Index (medulla/shaft diameter)
human hair generally <1/3
animal hair >=1/2
Medullary Shape
human => normally cylindrical
Animal => varies by species
Native Americans and Asians have continuous medulla

11. 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.

12. Chapter 5
Hair Shape
Can be straight, curly, or kinky, depending on the cross-section, which may be round, oval, or crescent-shaped.
Oval
(Curly)
Crescent moon
(Kinky)
Round
(Straight)
American and European whites, mexicans, and middle easterns
Generally Asians and Native Americans
African
Kendall/Hunt

13. Race
Appearance
Pigment granules
Cross section
other
European
Straight or wavy
Small and evenly distributed
Oval or round
Color may be blond, red, brown, or black
Asian
Straight
Densely distributed
round
Shaft tends to be course and straight
Thick cuticle
Continuous medulla
African
Kinky, curly or coiled
clumped
flattened

14. Shape of Hair
The physical characteristics of hairs provide information about which part of the body they came from
Hair from a beard is course and triangular in cross section
Beard hair with double medulla
Arm or leg hair with blunt, frayed end
Pubic hair showing buckling

15. Pencil ANalogy
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. Shape of the pencil is the cross section, the pencil point is the tip and the eraser is the root.

16. Hair growth
If hair comes out in this stage it has follicular tissue attached, looks stretched and pigment granules may be seen because hair is still growing
Follicles are ready to push out mature hair.
Bulblike shape of root, few pigment granules near it

17. Hair growth stages (Remember ACT):
Anagen: hair follicle is actively producing the hair; follicle is attached to root ( days)
Catagen: transition stage in which the root is pushed out of the follicle (14-21 days)
Telogen: hair naturally becomes loose and falls out (100 days) hairs on your brush or comb are in this stage
Forcibly removed
Fallen out

18. Hair Growth The tip of a mature hair will taper to a point
A recently cut hair will be squared off for 2-3 weeks
An abused hair will have split ends (dryness, lack of care, harsh chemicals, blow dryers etc)

19. Forensic Analysis of Hair
The following questions apply to hair evidence:
Is the hair human or animal?
Does it match the hair of the suspect?
Does it have a follicle for DNA testing?
Cat
Human

20. Collection of Hair Evidence
Questioned hairs must be accompanied compared with an adequate number of control samples
from victim
from suspects
From animals
Representative control samples
50 full-length hairs from all areas of scalp
24 full-length pubic hairs

21. Class Evidence
The more characteristics that are similar the greater the degree of probability of association
A single significant difference between the questioned (unknown) and the exemplar (known) sample will rule out a suspect
DNA can only be done on the root of the hair

22. Hair as a Chemical indicator
Hair can collect materials that were in the body
Type of test
Length of time
analogy
Blood
Few hours
snapshot
Urine
3-5 days
Time exposure
Hair
Months (shows specific patterns of use)
Album

23. It’s time to examine some hairs!

24. Can you identify the animal hairs shown?B C D G E F H I
Teacher Note: I challenge students to identify each hair sample pictured on this slide as they examine the sets of animal hairs I have prepared for them. An observation worksheet is available on my website which requires students to draw an image of what they see and add a description that highlights unique characteristics of each specimen. A key for the animal hairs is available on the next to last slide of this presentation!
Think About It …
In which samples are we viewing the cuticle? How do they compare?
(2) In which samples are we viewing the medulla? How do they compare?
(3) What characteristics can be used to identify hair samples?

25. Answer Keys

26. Types of Animal Hairs - Key
Cat
Horse
Pig
Human A B C D G E F H I
Deer
Dog
Rabbit
Rat
Human