1. A Lesson on
Hair
Identification
Forensic Science

2. 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.
Hair color is mostly the result of pigments, which are chemical compounds that reflect certain wavelengths of visible light.
Hair shape (round or oval or flat) 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.). )

3. The body area (head, arm, leg, back, etc
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 nuclear DNA, the root must be present. The hair may also be tested using mitochondrial DNA whether or not the root is present.

4. While hair is growing beneath the epidermis, it's outer covering is soft.  Once it goes past the epidermis, the outside layer hardens into keratin.
Inside the follicle, the hair is growing and is "connected" to blood vessels and nerves.
Outside the skin, the hair is essentially dead.

5. Parts of Hair Three main regions: root, shaft, and tip
Root: The part that was growing in the follicle.  This is the widest part of the hair
Shaft:  The middle of the length of the hair (from the root to the tip).  This is where the hair tapers
Tip:  The end of the hair farthest away from the root.  The hair is narrowest at the tip

7. Hair Structure: Three Major Layers
Hair is composed of three principal parts:
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.

9. 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.

10. 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.

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. Types of Medulla (Human)
Continuous – no breaks in medulla
Interrupted--few short breaks
Fragmented--few parts of medulla
visible
Absent--no medulla visible

13. The medulla of hair is made up of cells that run through the cortex
Interrupted, fragmentary, and absent medulla are found only in Humans.

14. Types of Medulla (Non-Human)
Uniserial ladder
Multiserial ladder
Lattice

15. Animal medulla can be similar to human, or one of a few other types
Animal medulla can be similar to human, or one of a few other types.  It is generally a much larger part of the hair than human medulla

16. Medullary Index
The medullary index of hair can be determined by the diameter of the medulla relative to the diameter of the hair, expressed in fraction.
Human: medullary index is less than one third of the hair diameter (1/3 or less)
Non-Human: medullary index is ½ or greater

17. Growth Stages of the Hair:
3 major growth stages: anagen, catagen, telogen
Anagen Stage:  The active growth phase of the hair follicle. 
Catagen Stage:  The transition period between growth and rest.  Hair continues to grow, but at a decreasing rate.  The root bulb looks elongated from being pushed out of the follicle.
Telogen Stage:  The rest period for the follicle.  The current hair is shed and no new growth takes place for a period of time.

19. Some Examples of Hair Types (Human)
Caucasian:
Shaft diameter: moderate with little variation
Cross Section: oval
Pigment granules evenly distributed

20. African:
Shaft diameter: fine to moderate with considerable variation
Cross Section: flattened
Pigment granules: clumped

21. Asian:
Shaft diameter: moderate with little variation
Cross Section: round
Pigment granules: large patchy areas

22. Hair Identification
Hair is generally used as a class characteristic not an individual characteristic:
Individual:  can be related to a particular person or thing
Class: can be related to groups of people or things
Using hair samples to ID a particular individual is very difficult

23. Steps of Hair Examination and Identification
1.Determine whether the hair in question originated from an animal or a human being 2. If it is human, the examiner compare the microscopic characteristics of the known and questioned hairs to see if they can make a match 3. If it is an animal, an examiner will further identify it to a particular type of animal, particular animal species.

24. 4. Forensic scientist also examines the hair sample through microscopic study for:
- Body area determination
- Racial determination
- Age and Gender
- Treatment and Removal
- Biological or Environmental Alteration

25. Hair as Evidence
Because hairs can be transferred during physical contact, their presence can associate a suspect to a victim or a suspect/victim to a crime scene. The types of hair recovered and the condition and number of hairs found all impact on their value as evidence in a criminal investigation. Comparison of the microscopic characteristics of questioned hairs to known hair samples helps determine whether a transfer may have occurred.

26. The examination of human hairs in the forensic laboratory is typically conducted through the use of light microscopy. This examination routinely involves a two-step process—the identification of questioned hairs and the comparison of questioned and known hairs. The purpose for conducting this examination is to ascertain whether two or more individuals could have come into contact or whether one or more individuals could have come into contact with an object.

27. This associative evidence is particularly useful in crimes of violence, such as homicide, sexual assault, and aggravated assault, where physical contact may have occurred.
Crimes such as burglary and armed robbery typically involve the recovery of debris and articles of clothing which may contain hairs useful for the identification of suspects.

28. Significance of Hair Evidence
The significance of hair examination results is dependent on:
1. The method of evidence collection used at the crime scene
2. The evidence processing techniques employed
3. The methodology of the hair examination process
4. The experience of the hair examiner.
Head hairs and pubic hairs are routinely held as more significant than hairs from other body areas.