Hair and Fibers - Forensics

Medulla

Central core of the hair.

Can classify hair depending on the appearance.

Medullary Index

Measures the width of the medulla relative to the width of the hair

Hairs that fell out during telogen

Hairs pulled out during anagen or catagen

Broken-torn hair

Cut hair

Fibers as evidence

-class evidence

-difficult to trace a back to a specific source

Natural Fibers

Come from animals, plants, and mined minerals.

Animal Fibers

-Made of proteins.

-wool

- cashmere, mohair

- angora

-Silk

Plant Fibers

-Made of cellulose

- cotton

- hemp

Mineral Fibers

-Made of inorganic, naturally occurring material.

~Asbestos

Synthetic Fibers

- usually made from fossil fuels

-man-made

Cortex

Inner layer of hair containing pigments and cortical fusi (air sacs).

Cuticle

Outside covering of hair, made of overlapping scales.

Coronal cuticle

Imbircate cuticle

Spinous cuticle

Human medulla may be

Fragmented, continuous, absent

Medullary index for humans

Less than 1/3 (33%)

Medullary index for animals

Greater than 1/2 (50%)

Round hair shape

Straight hair

Oval hair shape

Wavy hair

Crescent hair shape

Spiral curled, super curly hair

Anagen

Hair that is actively growing

Telagen

Hair that is dying or ready to fall out

Catagen

Hair that is in a resting phase

Rate at which hair grows

1cm/month

How long anagen phase can last

up to 5 years

Hair spends most of its time in this phase

Anagen

Cotton

Most common natural fiber

Polyester

Most common synthetic fiber

Locard's Exchange Principle

Explains why hair and fibers are the most common trace evidence: they are often picked up and dropped off by unknown people.

Follicle

Tissue in the skin that grows the hair

Picture of animal hair

Picture of human hair