1

Chapter 5 Hair

2

Class evidence

• Circumstantial evidence – lots of people have same hair color• Places someone at the scene• Only becomes individual evidence if

skin or cells attached – then DNA is the individual evidence

3

“Hair” are the facts…• Avg human body has ~ 5 million hairs – most

fine, down like

• Hairs are continuously shed and renewed at a rate of 100/day so not surprising that it is at a crime scene

• Head hair:• Blonds have ~ 120,000• Black, brown ~ 100,000• Redheads ~ 80,000

4

Hair Morphology• Protein polymers (molecule consisting of many identical

repeating units)

• Hair grows from a follicle (tube-like structure in the dermis) which is linked to the blood supply so whatever substances are taken into the body they are distributed to the hair growing at that time

• Hair shaft extends out through the epidermis and ends at the tip

5

Hair Morphology: Hair Shaft

• Cuticle – clear outer covering; tough overlapping scales

• Cortex – keratin molecules that run parallel to the length of the shaft; contains pigment that makes hair black, brown, yellow, red; no pigment = white, gray; cortical fusi - air spaces in the cortex that have to be seen w/ high power microscope.

• Medulla – row of cells along center of cortex; human hairs have either fragmented or no medulla except Native Americans and Asians – continuous medulla

6

Hair Shape• Depends on cross section of shaft • Round – straight hair• Oval - curly• Crescent-shaped – kinky

• Can also be twisted or undulated (slightly wavy)

7

Hair Growth

• Coarser hairs grow slower and fall out less frequently• ~ 1cm per month• Replaced every 3 to 5 years

• 3 stages of growth:

• Anagen – 80-90% of hair follicles at any one time

• Catagen – intermediate stage; lasts about 3 weeks

• Telogen – 8-10% of hair follicles; lasts 2-6 months; loss of hair

8

9

10

Anagen hair root

telogen hair root

Catagen hair root

Recently cut hair

?

11

Hair appearance• How would the following appear different:• Recently cut• Hair in brush• Hair pulled out from scalp• Cut 2-3 weeks ago

• Colored hair• Unconditioned hair• Split ends • Over heated (blow dryer, curling iron, etc.)

12

So what exactly can be determined from hair evidence?

• Whether the source is animal or human• Racial origin (sometimes)• Location on source’s body• If hair has been chemically treated (dyed, permed,

straightened)• Color• If hair was forcefully removed

13

Hair as a chemical indicator• Chemicals enter cortex of

the hair• Drugs• Metabolites (product of a

substances after a chemical reaction – after body metabolizes the chemical)

• Vitamins• Poisons (heavy metals –

arsenic, lead, mercury)• Oils in hair may contain

substances from environment – smoke from crack; (risk of false positive)

14

Hair from a crime scene

1. Determine human or animal – what type of animal

15

2. Determine race