Hairs and Fibers

HAIRS AND

FIBERS

HAIR OBJECTIVES• Recognize and understand the cuticle, cortex

and the medulla areas of hair• Describe the three phases of hair growth• Identify differences between animal and

human hairs• Explain proper collection of forensic

hair/evidence fibers• Describe and understand the role of DNA

typing in hair comparisons

FIBERS OBJECTIVES

• Identify the difference between natural and manufactured fibers.

• Describe collection procedures for fibers

What is Hair?

• An appendage of the skin that grows out of an organ known as the hair follicle.

• Structure – Root inside follicle– Shaft– Tip End

SHAFT STRUCTURE

Cuticle• The scale structure covering the exterior of the hair.

• Overlapping scales that always point toward the tip end of each hair.

* Formed from specialized cells that have hardened and flattened as the hair grows

Cuticle (or scale) Pattern will not individually identify a suspect

One of the factors used to differentiate between Human and Animal Hair

CORTEX

• Contains pigment granules

• Granules are used for points of comparison– Color– Size– Distribution

MEDULLA

• Central canal of cells• Not always present– If present, not always consistent

• Diameter is known as Medullary Index– Human Index is less than 1/3 – Animal Index is ½ or greater

TYPES OF MEDULLAS

• A) Fragmented– Uneven breaks in the

medulla• B) Interrupted– Even breaks in the

medulla• C) Continuous– Always constant

HAIR GROWTH PHASES• Anagen

– Initial growth phase– Hair actively produced– Up to 6 years– Follicular Tag for DNA

• Catagen– Transition between An and Tel– Growth retards– Hair separates from blood

supply– Lasts 1-2 weeks

• Telogen– Hair growth ends– Hair sheds– 2-6 months

HAIR ANALYSIS

• 1) Determine whether it is human or animal hair– HOW?

• Scale Pattern• Medulla Shape• Medulla Index

• 2) Determine hair origin• 3) Compare hair sample to known reference

standards– Must come from same area of body

Race Ancestry Medulla Pigmentation Cross Section

Caucasoid European Frag/Not Present Straight or Wavy, Fine coarse, more evenly

distributed than Negroid

Oval/Round

Mongoloid Asian Continuous Very Dense, even distribution

Thick cross section

Negroid African Frag/Not Present Kinky, dense, unevenly

distributed

Flat/Oval

EVIDENCE COLLECTION

• 50 full length from head• 24 full length from pubic area• Reference samples MUST BE from same area

of the body

FIBERS

• Class of materials that are continuous filaments or are in a discrete elongated pieces, similar to lengths of threads.

• Different Types– Natural Fibers– Manufactured Fibers

FIBERS

• Manufactured– Derived from either

natural or synthetic polymers

– Consists of regenerated (raw materials) and synthetic fibers (polymers)

– Acrylic, Rayon, Acetate

• Natural– Derived from animal or

plant– Same procedure as

human hair– Most common is cotton– Linen and wool

FIBER ANALYSIS

• PLM or Comparison microscope used• Study – Cross section– Presence of specific particles– Color– Diameter– Striations on surface of fiber

FIBERS ANALYZED USING PLM

Cotton

LinenWool

FIBER COLLECTION

• Use a vacuum to collect fibers.• Also use:– Scraping – Tape lift– Picking– Shaking