1. Hair & Fiber Analysis

2. How Many Hairs Do You Shed Per Day?

3. 50 - 100 (Locard was pretty smart)

4. By the end of this unit, you will be able to…
Describe the parts/structure of hair including follicle, medulla, cortex, and cuticle
Distinguish between human & animal hair
Make or rule out a class match between hairs
Explain how hair is used in a forensic investigation
Calculate medullary index to help hair ID

5. Why Do Animals Have Hair?
Trap body heat
Protect against friction/abrasion
Block sunlight
Enhance sense of touch or motion
Vestigal (human body hair)
Vestigal means no longer
having a function due to
evolutionary changes.

6. Hair Follicle (Part we see = shaft)
- Part of hair under skin where hair forms & grows
(Part we see = shaft)
If hair is forcibly removed it may have a “tag” of skin cells from the follicle

7. Hair with Follicle Attached
Only if forcibly removed
Could get DNA
Could get blood type
Hair that falls out naturally or is cut lacks the follicle

8. Structure of Hair Shaft
Thin, outer cuticle (scaly appearance)
cortex (thick part under cuticle containing pigment)
Medulla (inner core that may
or may not have pigment)
- all made of keratin (protein)
which is also fingernails,
rhinoceros horn, and more!

9. Analogy For Hair Structure…

10. CUTICLE Thin, colorless, outermost layer made of overlapping scales
The structure of the scales is different for humans vs. various kinds of animals
Scales always point toward tip of hair
Human
Deer

11. Cuticle Types
Spinous Coronal Imbricate
Spinous: scales look like petals (animals only, including cats)
Coronal: scales look like stack of crowns (animals only, including rodents)
Imbricate: flat, narrow scales (human)

12. SPINOUS
CORONAL

13. Cortex Thickest part (in humans) Contains most of the pigment
Pigment comes in “granules” that are more visible in some hair as dots of color
ARROW SHOWS CORTEX

14. Medulla
BEAVER
HUMAN
DEER
CAT

15. Medulla (types for class matches)

16. CONTINUOUS—NO BREAKS
INTERRUPTED—SEGMENTS
FRAGMENTED—RANDOM BREAKS
NO MEDULLA

17. HAIR CHARACTERISTICS All characteristics are often but not always true
Racial patterns—can’t really ID race by hair—but a straight blond hair is almost certainly not from a person of African descent
Individual variation—your hairs are not all identical (50 samples taken!)
Body area variation—examples to follow
Length can be useful but obviously changeable

18. COLOR
Granule size varies (some people have larger pigment granules & grainy-looking cortex)
Banded only in animals (see picture below)
More pigment closer to cuticle in humans, closer to or in medulla in animals
PIGMENT CLOSER TO CUTICLE
PIGMENT ALL IN MEDULLA

19. CROSS-SECTION Circular [top picture]
Asian
Head
some body hair
Oval (Caucasian; head) [middle pic]
Flattened (African) [bottom pic]
Triangular
Beard hair
Some body hair
Diameter
Larger for Asian
smaller for African

20. TEXTURE Coarse (rough/tough/less flexible)
most animal hair is very coarse
beard, pubic hairs more coarse (humans)
Fine (soft/thin/very flexible)
Caucasians
children
Blunt tip
Body hair
Tapered tip
eyebrows/lashes
BLUNT TIP

21. SHAPE straight (European, Asian) wavy (European)
kinky or coiled (African)
buckled (pubic hair)
KINKY HAIR
BUCKLED HAIR

22. MEDULLA Double Medulla Thickness some beard hair
thicker medulla for animals
Medulla index calculation
DOUBLE MEDULLA
THICK ANIMAL MEDULLA

23. Medullary Index Index = (Width of Medulla) / (Width of Entire Hair)
0.33 or less = human (smaller medulla)
0.5 or more = animal (larger medulla)

24. Hair Source -- Area of Body
Head
Eyebrows/lashes
Facial hair
Body hair
Underarm hair
Pubic hair

25. Alteration of Hair
Bleaching – makes hair yellowish, removes pigment, damages the cuticle scales
Dyeing – colors the cortex and the cuticle (cuticle normally has no color)

26. Detecting Foreign Substances in Hair
Poisonous metals (lead, arsenic) and some drugs get incorporated into hair as it grows
Hair resists decomposition, so the toxins remain trapped in the hair for a long time
Hair growth rate can determine how long ago the poisoning or drug use occurred

27. Hair Growth Rate
Hair grows at a rate of about 0.44 mm/day (1.3 cm/month)
Some poisons and drugs accumulate in hair
Provides timeline for when poisoning occurred
Ex: A hair is found with traces of arsenic extending 25 mm from the follicle. How long has he been ingesting the poison?
25 mm / 0.44 = about 57 days (a couple months)

28. Neutron Activation Analysis
uses radiation from a nuclear reactor to detect the concentration of various metals in hair.
Exact concentrations of each metal will vary from one individual to the next, providing a near-individual match (such as 1 in a million)