The Study of Hair

Introduction

• A hair without the follicle and its nuclear DNA cannot provide individual evidence but can yield class evidence

• Chemical tests performed on hair can reveal drugs, toxins, heavy metals, and nutritional deficiencies 

• mtDNA from hair can reveal some of a suspect’s or victim’s family relationships

  • Mitochondrial DNA is the same as that of mothers

• Cuticle is dissolved when analyzing hair

History of Hair Analysis

• 1883: Alfred Swaine Taylor & Thomas Stevenson covered hair in a forensic science text

• 1910: Victor Balthazard & Marcelle Lambert published  a comprehensive study of hair

• 1934: Dr. Sydney Smith analyzed hairs side by side using a comparison microscope

• Today: Standard procedures of hair analysis included microscope examination and DNA analysis

The Function of Hair

• Regulates body temp

• Decreases friction

• Protects against sunlight

• Acts as a sense organ

• humans are born with about 5 million hair follicles, does not regenerate and losses as they get older

The Structure of Hair

• Hair consists of a follicle embedded in the skin that produces the shaft

  • Goes through the epidermis, dermis, and subcutis (which is where the root is developed)

  • Follicle holds the root in place and helps to nourish the hair and help it grow

  • Nerves are attached to the root allowing for assisted senses

  • Sebaceous gland secretes oil and is what causes hair to be oily or dry

  • Shaft (outer portion exposed to outside environment) 

• Shaft is composed of the protein keratin and consists of the outer cuticle, cortex, and inner medulla (all 3 vary among individuals or species)

• Hair growth is broken down into three developmental stages, the anagen (growth), catagen (growth and change), and telogen (dormant) 

***Note: The only time you can do nuclear DNA analysis on hair is if the cuticle is still attached to the hair follicle, which will only occur if the hair is forcefully removed; Mitochondrial DNA can still be analyzed without follicle 

• Hair shaft is made up of three layers:

  • Inner medulla- innermost section

  • Cortex- mid-section 

  • Outer cuticle- protective layer

• Cuticle is a transparent outer layer of the hair shaft

• Patterns of growth can help identify the species of origin of the hair

Types of Medulla Patterns:

• Continuous

  • Unbroken line  of color

• Interrupted (intermittent)

  • Even intervals of color ( line broken at regular intervals)

• Fragmented or segmented

  • Pigment line unevenly spaced

• Solid

  • Hair is so pigmented that you can’t see medulla line

• None

  • No separate pigmentation in the medulla

    • Ex: with bleached hair (no medulla with bleach)

Types of Hair

• Human hair varies from person to person 

• Hair from different body parts have different traits 

  • Arm or leg hair with a blunt, frayed end

  • Pubic hair = showing buckling

  • Beard hair with double medulla 

Life Cycle of Hair

• Anagen

  • Lasts about 10-0 days

• Catagen stage

  • Hair stops growing & follicle recedes

• Telogen stage

  • Hair follicle is dormant and hair is easily lost 

Treated Hair

• Hair can be treated in many different ways

  • Dyed hair can affected the color of the cortex

Ethnic or Ancestry Differences

• Some key physical characteristics that are associated with hair of different ancestral groups 

  • European → straight or wavy

  • Asian → Densely distributed and shaft tends to be straight, thick cuticle, round with a large diameter, black in color

  • Africa → Kinky, curly, or coiled, may be buckled (cross section is flattened more oval like)

Animal Hair vs Human Hair

• Pattern of pigmentation

• Medullary index= diameter of medulla/diameter of hair

  • 0.5 or greater → animal (we’re gonna go with 0.33 or greater is animal)

  • 0.33 or less → human

• Cuticle type 

Hair Cuticles

• The cuticles of the hair shaft can help distinguish human hair from other animal hair

  • Imbricate

  • Coronal

  • Spinous 

Electron Microscope

• Electron microscopes direct a beam of electrons at a sample

• Electron microscopes provide a magnification of 50,000 times or more

Hair Examination and Testing 

• DNA is amplified by PCR

• DNAis profiled using an automated process

• mtDNA can be used to establish a genetic relationship through the mother

• Suspects can be excluded if their mtDNA is not consistent with the crime scene mtDNA 

  • Can help exclude victims