1. Hair Analysis
Forensic Science

2. 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.

3. Did You Know? Chaetophobia is the fear of hair.
Tonsurphobia is the fear of haircuts.

4. Did You Know?
An average human scalp contains 100,000 hairs and most people lose between 25 and 125 hairs a day.

5. Did You Know?
Hair generally grows at a rate of approximately 3/16” per day, or approximately ½” per month.

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

7. Properties of hair that make it useful to criminalists:
small
easily shed
clings to clothing and other materials

8. 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

9. How hair (and fiber) evidence is useful to criminalists:
Helping to establish the scope of the crime scene
Placing a perpetrator at a scene
Connecting a suspect with a weapon

10. How hair (and fiber) evidence is useful to criminalists:
4. Supporting witness statements
5. Connecting crime scene areas (abduction, vehicle used, dump site)

11. 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.

12. Hair Differences
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

13. External Hair Anatomy
Hair grows out of the skin from a pocket of specialized cells called a follicle.

14. Hair Follicle

15. 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.

16. 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.).

17. 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.

18. Stages of Hair Development:
Anagen: growing
Catagen: at rest
Telogen: dying

19. Two Parts of Hair
The shaft of the hair projects from the skin, and the root lies below the epidermis.

20. Hair Root
The root of a mature human hair is similar in appearance to a flower bulb.

21. External Part of Hair
The root end is called the proximal end and the growing tip end is called the distal end.

22. Hair Shaft
The shaft of the hair is made up of three parts: cortex, cuticle, and medulla.

23. Hair Structure 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.

24. Hair Cuticle
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.

25. Hair Cuticle
Scales overlap and always point up the shaft, away from the bulb.

26. 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.

27. Types of Cuticles Coronal (crown like) scales
Spinous (petal like) scales
Imbricate (flattened) scales

28. Coronal Cuticle (crown like)
give the hair a mosaic surface appearance. Human hair rarely has these scales, but they’re common among rodents

29. Spinous Cuticle (petal like)
tend to be somewhat triangular in shape. These scales aren’t found in humans but are typical of cats.

30. Imbricate Cuticle (flattened)
scales are found in humans and many other animals.

31. Imbricate Cuticle (human)

32. Different Types of Cuticles

33. 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.

34. 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.

35. Medulla of Hair
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.

36. Medulla’s Appearance Fragmented (trace) Intermittent (discontinuous)

37. Basic Structure of the Medulla
Uniserial (Rabbit)

38. Basic Structure of the Medulla
Multiserial (Rabbit)

39. Basic Structure of the Medulla
Vacuolated (dog)

40. Basic Structure of the Medulla
Lattice (deer)

41. Basic Structure of the Medulla
Amorphous (human)

42. Checklist of Comparisons
Color and width
Distribution pattern of the medulla
Color and distribution pattern of pigment in the cortex
Cuticle pattern

43. Hair Root of a Cat
The frayed end is character-istic of a cat root.

44. Hair of a Cat
The uniserial or lader like medulla in this slide is also that of a cat.

45. Hair of a Rabbit
This multiserial medulla composed of many ladders is characteristic of hair from a rabbit.

46. Hair of a Seal
The spinous scale pattern of seal hair is easily observable without preparing a scale cast.

47. Hair of a Human
The human scale pattern is not as easily observable under a whole mount. This scale cast enhances the pattern.

48. Hair of a Human
This club-shaped human root is characteristic of dead or dying root in telognic stage.

49. Plucked Hair
A human hair that has been forcibly removed will have a root that looks like this. Part of the follicle will be attached.

50. Cut Hair
A hair that has been freshly cut with scissors will look like this. Notice the ragged edge and sharp corners.

51. Cut Hair
A hair with rounded corners indicates that the hair has not been freshly cut.

52. Dyed Hair
This hair has been dyed. Notice the even color distribution cross section of the hair.

53. Dyed Hair
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 hair was dyed.

54. Hair
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.

55. A Louse
External environment also can play a role in hair examinations. This picture reveals the outline of a louse.