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HAIR ANALYSIS

HAIR ANALYSIS. Hair. Hair grows from a hair follicle The parts of a hair include the bulb, root, and shaft The 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

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HAIR ANALYSIS

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  1. HAIR ANALYSIS

  2. Hair • Hair grows from a hair follicle • The parts of a hair include the bulb, root, and shaft • The 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

  3. Hair (cont.) • The shaft of the hair is made up of keratin and has 3 layers: • Cuticle • Cortex • Medulla

  4. The Cuticle • Transparent, outermost layer that helps hold the medulla and cortex together • Scale-like in appearance, the scales point away from the scalp

  5. The Cortex • Surrounds the medulla and consists of flattened cells • It is the largest part of the hair shaft • This layer contains the pigment (melanin) that gives hair its color

  6. The Medulla • The medulla is the central part of the hair and is made up of large cells separated by air spaces; it can be:

  7. Medullary Index • A ratio of the size of the medulla compared with the size of the entire hair • MI = x/y where x is the medullary diameter and y is the total diameter

  8. MedullaryIndex (cont.) • In humans, the MI is less than 1/3 • In animals, the MI is greater than ½

  9. Pigmentation: Human vs. Animal • Human 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

  10. Cuticle: Human vs. Animal • Some 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

  11. Types of Hair • Scalp: has a uniform diameter in cross-section • Beard: coarse, curved, and when viewed in cross-section has a distinctive triangular shape • Eyebrow, nose, ear, and eyelid: shorter and stubbier than scalp hair and have wide medullas • Axillary: have unevenly distributed pigments; end in a fine point when uncut • Auxiliary: oval or triangular, depending on whether the body region has been regularly shaved • Pubic:oval or triangular

  12. Hair Growth Hair proceeds through 3 stages as it develops: • Anagenstage: • hair actively grows • cells around the follicle rapidly divide and deposit materials in the hair • 80-90% of hairs are in this stage • Catagenstage: • hair grows and changes • 2% of hairs are in this stage

  13. Hair Growth (cont.) • Telogenstage: • follicle becomes dormant • hair easily lost during this stage • 8-18% of hairs are in this stage

  14. Hair Dyes • Cause hair to have less pigment granules • Hair 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

  15. Forensic Hair Analysis • When 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

  16. Race Determination • African: 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

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