Form & Structure of HairForm & Structure of Hair

Hair is frequently found at a crime sceneHair is frequently found at a crime sceneLocard Exchange PrincipleLocard Exchange Principle

Hair is considered class evidenceHair is considered class evidenceCould possibly be individualized if root tissue Could possibly be individualized if root tissue

is still attached to the hairis still attached to the hairVery useful in supporting Very useful in supporting

circumstantial evidence circumstantial evidenceCan be used to place someone Can be used to place someone

at the crime scene at the crime sceneCan link a criminal with the crimeCan link a criminal with the crime

From hair, one can determine:From hair, one can determine:

If the source is human or animalIf the source is human or animal

RaceRaceo SometimesSometimes

Based on shape of hairBased on shape of hair

Origin of the location on the source’s bodyOrigin of the location on the source’s body

Whether the hair was forcibly removedWhether the hair was forcibly removed

o By whether or not root attachedBy whether or not root attached

Whether the hair has been treated with Whether the hair has been treated with chemicalschemicals

If drugs have been ingestedIf drugs have been ingested

Human body has about 5 million hairsHuman body has about 5 million hairso Most are downy hair covering bodyMost are downy hair covering body

Hair is continuously shed & renewed Hair is continuously shed & renewed throughout lifetimethroughout lifetimeo About 100/24 hour period on head aloneAbout 100/24 hour period on head alone

Much higher rate of loss for body hairMuch higher rate of loss for body hair

Hair on the headHair on the heado Blonds have most – about 120,000 strandsBlonds have most – about 120,000 strandso Redheads have least – about 80,000 strandsRedheads have least – about 80,000 strandso Black/Brown in the middle – about 100,000 Black/Brown in the middle – about 100,000

strandsstrands

Must understand structure of hair to Must understand structure of hair to analyze itanalyze it

Made up of cross-linked protein polymersMade up of cross-linked protein polymerso Very resistant to breaking downVery resistant to breaking down

Grows from a tube-like organ called a Grows from a tube-like organ called a folliclefollicleo Located in the dermisLocated in the dermis

Follicle is linked to the body’s blood Follicle is linked to the body’s blood supplysupplyo Whatever is taken into body is distributed Whatever is taken into body is distributed

to part of hair growing at that timeto part of hair growing at that timeo Important in analyzing hair for drugs & Important in analyzing hair for drugs &

poisonspoisonsHair shaft extends through Hair shaft extends through

epidermis & ends at tip epidermis & ends at tipo Shaft composed of Shaft composed of

dead cells dead cells

Composed of three parts:Composed of three parts:oCuticleCuticle

Clear, outer covering of shaftClear, outer covering of shaftMade of tough, overlapping scalesMade of tough, overlapping scales

Scales finer in humans compared to animalsScales finer in humans compared to animalsoCortexCortex

Made of protein called keratinMade of protein called keratinEmbedded with pigment that gives hair colorEmbedded with pigment that gives hair colorContains air sacs called cortical fusiContains air sacs called cortical fusi

Different shapes & sizesDifferent shapes & sizesPossible class characteristicPossible class characteristic

oMedullaMedullaCanal running down center of cortexCanal running down center of cortexMay be dark or translucent depending on May be dark or translucent depending on contentscontents

Outer most layer of hair covered with scalesOuter most layer of hair covered with scalesScales point toward tip of the hairScales point toward tip of the hairScales differ among species of animalsScales differ among species of animals

o Named based on their appearanceNamed based on their appearanceThree basic scale patterns include:Three basic scale patterns include:

o CoronalCoronal Mouse Mouse

o SpinousSpinous Cat Cat

o ImbricateImbricate Human Human

To visualize scalesTo visualize scales::

Paint clear fingernail Paint clear fingernail

polish on a glass slide.polish on a glass slide.

When the polish begins When the polish begins

to dry, place a hair on to dry, place a hair on

the polish.the polish.

When it is almost dry, When it is almost dry,

lift off the hair and lift off the hair and

observe the scale observe the scale

imprints.imprints.

What pattern is seen in What pattern is seen in

this slide?this slide?

Gives hair its shapeGives hair its shape Has two major characteristics:Has two major characteristics:

oMelanin is pigment that gives hair its colorMelanin is pigment that gives hair its colorProduced by melanocytes located in the follicleProduced by melanocytes located in the follicle

oCortical fusi are air spaces usually found near Cortical fusi are air spaces usually found near

the rootthe rootSometimes found throughout the cortexSometimes found throughout the cortex

May be dark or translucentMay be dark or translucento Depends on whether it contains air, liquid, or Depends on whether it contains air, liquid, or

pigmentpigmentMay be continuous, interrupted, or May be continuous, interrupted, or

fragmentedfragmentedHuman hair usually lack a medulla or has Human hair usually lack a medulla or has

one that is fragmented one that is fragmented o Except for Native Americans & Asians whose Except for Native Americans & Asians whose

hair have a continuous medullahair have a continuous medullaAnimal hairs have wide variety of medullar Animal hairs have wide variety of medullar

patternspatternso Patterns can identify some speciesPatterns can identify some species

Hair’s core that is not always visibleHair’s core that is not always visible Comes in different types and patternComes in different types and pattern Patterns Include:Patterns Include:

oInterruptedInterruptedoFragmentedFragmentedoContinuousContinuousoStackedStackedoAbsentAbsent

Human medulla may be continuous, Human medulla may be continuous, fragmented, or absentfragmented, or absent

Determined by measuring the Determined by measuring the diameter of the medulla then diameter of the medulla then dividing it by the diameter of the dividing it by the diameter of the hairhairo MI = MI = medulla diametermedulla diameter x 100 x 100 hair diameterhair diametero Medullary index for human hair is Medullary index for human hair is

generally <33 generally <33o Medullary index for animal hair is Medullary index for animal hair is

generally >50 generally >50

Deer MI = 100 Raccoon MI = 80 Human MI = 25

May be straight, curly, or kinkyMay be straight, curly, or kinkyoDepends on the cross-sectionDepends on the cross-section

Cross-section may be:Cross-section may be:o RoundRoundo OvalOvalo Crescent-shaped:Crescent-shaped:

RoundRound(Straigh(Straigh

t)t)

OvalOval(Curly(Curly

))

Crescent moonCrescent moon (Kinky)(Kinky)

Asians & Native AmericansAsians & Native Americanso Round cross section & no twistingRound cross section & no twisting

Caucasians, Mexicans, & Middle Eastern Caucasians, Mexicans, & Middle Eastern heritageheritageo Oval cross section & rarely twist Oval cross section & rarely twist o Evenly distributed pigmentationEvenly distributed pigmentation

African heritageAfrican heritageo Crescent-shaped cross section with a twistCrescent-shaped cross section with a twisto Dense, clumped pigmentation Dense, clumped pigmentation

UndulatedUndulated

TwistedTwisted