HAIR ANALYSIS

HairHair grows from a hair follicleThe parts of a hair include the

bulb, root, and shaftThe bulb is an expansion at the

end of the hair from which the rest of the hair grows

The root of the hair is the part of the hair that is embedded in the skin

The shaft of the hair is the part that can be seen

Hair (cont.)The shaft of the hair is made up of keratin and

has 3 layers: CuticleCortexMedulla

The CuticleTransparent, outermost layer that helps hold

the medulla and cortex togetherScale-like in appearance, the scales point

away from the scalp

The CortexSurrounds the medulla and consists of

flattened cellsIt is the largest part of the hair shaftThis layer contains the pigment (melanin)

that gives hair its color

The MedullaThe medulla is the central part of the hair

and is made up of large cells separated by air spaces; it can be:

Medullary IndexA ratio of the size of the medulla compared

with the size of the entire hairMI = x/y where x is the medullary diameter

and y is the total diameter

Medullary Index (cont.)In humans, the MI is less than 1/3In animals, the MI is greater than ½

Pigmentation: Human vs. AnimalHuman hair tends to have more pigment

toward the cuticle while animals have more pigment towards the medulla

Animal pigments are often found in solid masses called ovoid bodies while human hairs are usually one color along the length

Animal hairs can change color abruptly creating a banded pattern; humans do not have banded hair

Cuticle: Human vs. AnimalSome mammals (i.e. rodents and bats),

have scales that give the appearance of a stack of crowns; these are called coronal

Some mammals (i.e. cats, seals, and minks), have scales that resemble petals; these are called spinous

Humans have scales that are flattened and narrow; these are called imbricate

Types of HairScalp: has a uniform diameter in cross-sectionBeard: coarse, curved, and when viewed in

cross-section has a distinctive triangular shapeEyebrow, nose, ear, and eyelid: shorter and

stubbier than scalp hair and have wide medullasAxillary: have unevenly distributed pigments;

end in a fine point when uncutAuxiliary: oval or triangular, depending on

whether the body region has been regularly shaved

Pubic: oval or triangular

Hair GrowthHair proceeds through 3 stages as it develops: Anagen stage:

hair actively grows cells around the follicle rapidly divide and

deposit materials in the hair 80-90% of hairs are in this stage

Catagen stage: hair grows and changes 2% of hairs are in this stage

Hair Growth (cont.) Telogen stage:

follicle becomes dormant hair easily lost during this stage 8-18% of hairs are in this stage

Hair DyesCause hair to have less pigment granulesHair dyes will color both the cortex and the

cuticle so the cuticle’s inner margin is obscured or dark

Because hair grows at a rate of 1.3 cm per month, it is possible to determine the amount of time that has passed since the hair was dyed

Forensic Hair AnalysisWhen hair is found at a crime scene, forensic

scientists use the medullary index to determine if the hair is human or animal

If the hair is human, the part of the body from which it originated can be determined

Because hair from one part of the body are not always the same (brown hair with some gray), 50 hairs are usually collected from the suspect’s head

Race DeterminationAfrican: hairs are curly with

densely packed, unevenly distributed pigment granules; medulla is discontinuous or absent

European: often straight or wavy with pigment that is more evenly distributed; medulla is discontinuous or absent

Asian: straight with continuous medulla and thick cuticle