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Hair

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Do Now:

1.How are the layers of hair similar to the layers of a pencil2.How can hair be used in a forensic investigation

*If students are talking during Do Now – pop quiz (click here)

Objective: SWBAT identify the various parts of a hair. SWBAT describe the variations in the structure of the medulla, cortex and cuticle.

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Introduction

From hair, one can determine:

If the source is human or animal

Race (sometimes)

Origin of the location on the source’s body

Whether the hair was forcibly removed

If the hair has been treated with chemicals

If drugs (or poisons) have been ingested

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Form and Structure of Hair‡ Morphology – form and

structure of hair‡ Average human body has about

5 million hairs‡ Blondes average 120,000 strands of

hair on their head‡ Redheads have about 80,000‡ Black and brown hair people have

about 100,000

‡ Hairs are continuously shed and renewed at a rate of about 100 each 24-hour period from the scalp alone!

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Hair Shaft

Composed of:

Cuticle— clear outside covering of hair shaft, made of overlapping scales (pattern is used to determine species)

Cortex—inner layer made of keratin and embedded with pigment; also contains air sacs called cortical fusi

Medulla—inside layer running down the center of the cortex

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The Cuticle

The cuticle is the outermost layer of hair which is covered with scales. animals and are named based on their appearance. The three basic patterns are:

Coronal- mouse

Spinous- cat

Imbricate- human

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The Cortex

The cortex gives the hair its shape.

Melanin—give hair its color

Contains keratin – a tough protein

makes hair so resistant to chemical and biological degradation.

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The Medulla‡ Hair Core

‡ Most humans have no medulla or one that is fragmented (except Native Americans and Asians, where medulla is usually continuous)

Types:

Intermittent or interrupted

Fragmented

Continuous

Stacked

Absent—not present

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Human Medulla

Human medulla may be continuous, fragmented, or absent.

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Hair Classification Activity

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Exit Ticket

1. What are the three parts of the hair?2. Can the hair cuticle get you to an individual person? Why or why not?

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Medullary Index

Determined by measuring the diameter of the medulla and dividing it by the diameter of the hair.

Medullary index for human hair is generally less than 1/3.

For animal hair, it is usually greater than 1/2.

mouse

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Hair Shape and Cross Section

Can be straight, curly, or kinky, depending on the cross-section, which may be round, oval, or crescent-shaped.

Round(Straight)

Oval(Curly)

Crescent moon (Kinky)

Human hair ranges in diameter from 25-125 µm

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Racial Characteristics of Hair‡ Risky, but generally…

‡ Asians & Native Americans – round cross section with no twisting

‡ American & European whites, Mexicans, and people of Middle Eastern background – oval cross section, rarely with a twist or undulation.

‡ African heritage – flat to crescent-shaped cross section with twist, undulation and dense, clumped pigmentation.

Undulation – (in hair morphology) slight waviness

Undulated

Twisted

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Hair Growth

Terminology

Anagen—hair is actively growing; lasts up to 5 years; includes 80-90% of hair follicles

Catagen—hair is not growing; a resting phase

Telogen—follicle is getting ready to push the hair out; lasts two to six months; about 8-10% of hair follicles

Grows about 0.4 mm per day, or 1 cm per month; approximately one-half inch per month

Replaced about every 3-5 years with new hair

Coarser hairs grow at slower rate and fall out less frequently

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The Root

Human roots look different based on whether they have been forcibly removed or they are telogen hairs and have fallen out.

Animal roots vary, but in general have a spear shape.

Fallen out Forcibly removed

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The Tip

Tip of mature hair will taper to a point

Recently cut hair is squared off at the tip, but within 2-3 weeks the tip becomes rounded

Frayed hair tip results from over-processing (bleach, coloring, straighteners, blow dryer) or age

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Hair Comparison

Color

Length

Diameter

Distribution, shape, and color intensity of pigment granules

        

Scale types

Presence or absence of medulla

Medullary type

Medullary pattern

Medullary index• Dyed hair has color in cuticle and cortex

• Bleaching removes pigment and gives a yellow tint

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DNA from Hair

The root contains nuclear DNA. If the hair has been forcibly removed, some follicular tissue containing DNA may be attached.

The hair shaft contains abundant mitochondrial DNA, inherited only from the mother. It can be typed by comparing relatives if no DNA from the body is available. This process is more difficult and more costly than using nuclear DNA.

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Collection of Hair

Questioned hairs must be accompanied by an adequate number of control samples.

• From victim

• From possible suspects

• From others who may have deposited hair at the scene

Control sample

• 50 full-length hairs from all areas of scalp

• 24 full-length pubic hairs

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Hair Toxicology

Advantages:

• Easy to collect and store

• Is externally available

• Can provide information on the individual’s history of drug use or evidence of poisoning

Collections must be taken from different locations on the body to get an accurate timeline.

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Hair as Chemical Indicator

‡ Metabolite – a specific product of a substance, formed by chemical processes in the body

‡ Drugs and their metabolites, vitamins and poisons can be detected with just a few mm of hair.

‡ Provides back up to urine and blood testing‡ Drug metabolites only detectable in urine for

approx. 3-5 days from last use.‡ Hair grows at approx. 1 cm per month and will

record drug use over a longer period of time.

‡ Can establish dietary deficiencies and diseases

‡ Oils on scalp can deposit onto hair and will leave evidence of environment

‡ Smoke from crack cocaine can be deposited this way

‡ May provide a false positive

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Hair Toxicology, continued

Napoleon died in exile in 1821. By analyzing his hair, some investigators suggest he was poisoned by the deliberate administration of arsenic; others suggest that it was vapors from the dyes in the wallpaper that killed him.

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More about Hair

For additional information about hair and other trace evidence, check out truTV’s Crime Library at:

www.crimelibrary.com/criminal_mind/forensics/trace/1.html