Hair as Trace Evidence (Forensics)

Difference due to:

• Species
• Somantic Origin
• Cosmetic Treatment
• Race
• Age

Cuticle = Outside surface of hair

Cortex = Major part of hair mass

Pigment = contained within cortex - defines colour

Medulla = At centre of shaft, within cortex - normally filled with air and increases hair strength

Distal Terminus = tip of hair

Proximial Terminus = root of hair

CUTICLE

• Layer of cells  - outer surface of hair
• Cells overlap with free ends pointing towards distal terminus

3 types of cuticle

• Coronal (Crown-like) - rarley human (Rodent, bats, cats)
• Spinous (petal-like) - NEVER human (Seal, cats other mammals)
• Imbricate (flattened) - Human (and a few other animmals)

MEDULLA

• ABSENT

• CONTINUOUS

• DISCONTINUOUS

If Medullary Index (MI) less than or equal to 1/3 = human

If MI greater than 1/2 = animal

DISTAL TERMINUS - can tell how hair was cut and time since last treatment.

PROXIMAL TERMINUS - can tell how hair was shed, naturally or mechanially?

Can change colour, shape and chemistry of hair

Surface Treatment:

• Shampoo
• Conditioner
• Sprays
• Lotions

Whole Fibre Treatment:

• Colourants

Ideal physical evidence: -

• Significant amounts are lost unwittingly.

• Hair is chemically quite stable.

• DNA evidence can be obtained from a single hair providing individualisation of the sample.

Need to determine:

Species - human or animal?

Geographical Origin - Race

Somatic Origin - from where on body?

Head Hair

• Vary in length
• Tips often cut or split and rarely tapered
• Diameter varies very little along length

Pubic Hair

• Shorter, curlier, flatter cross section
• Continuous medulla

Limb Hair

• Finer and lighter in colour
• Slight Pigmentation
• 3-6mm in length

Eyebrows/lashes

• Short curved with tapared tips
• Large Medulla
• Relatively Coarse

Chest Hair

• Stiff texture
• Moderate diameter variation
• Tapered Tips
• Small Diamete than pubic hairs