Hair

Unit 4

I. The study of hair

• Hair is considered to be class evidence.

• Without follicle cells, it cannot be used to identify a specific individual.

• Hair is easily left behind… • It adheres to clothing, carpeting,

upholstery…• It transfers from one substance to

another, one location to another, quite easily.

• Hair has a tough outer covering enabling it to resist decomposition.

• The physical characteristics of hair can indicate racial background.

• Chemical tests can indicate drug history, the presence of toxins, and heavy metals as well as the individual’s nutritional history.

• When a follicle cell is present, DNA evidence may be available.

• Because DNA evidence is individual, its presence makes the hair sample individualized.

A. The function of hair• All mammals have hair.• In many, the hair is quite dense and is

called fur• It is reduced in most humans as it isn’t as

critical a feature as it is with other mammals.

• When humans are born, they have their greatest number of hair follicles: 5 million – 2% on their head.

• As we age the density of our hair decreases.

• Hair:– Reduces friction– Acts as a sensory organ– Protects against sunlight– Regulates temperature in association with

the muscles in skin.

• When conditions are cold, muscles pull the hair upright creating pockets that trap air – providing a warm, insulating layer next to the skin.

• When conditions are warm, muscles relax, flattening the hair releasing the trapped air.

B. The structure of hair

• Hair has two parts:– A follicle

and

a shaft

• The follicle is a “club-shaped” structure in the skin.

• At its end is a network of blood vessels (called the papilla) that supply nutrients to the hair helping it to grow

• The bulb surrounds the papilla…an oil secreting sebaceous gland is within the bulb helps condition the hair.

• The erector muscle that regulates temperature attaches to the bulb

• The hair shaft is made of keratin…a protein produced in the skin.

• This makes the hair strong and flexible

• Hair shafts are made up of three distinct layers:– The inner medulla– The cortex– The outer cuticle

1. Cuticle

• The transparent outer layer of the hair shaft

• made of scales that overlap and protect the inner layers.

• Scales point from proximal end to distal end

• The direction the scales point indicates where the younger and older ends of the hair are located.

• This is important in analyzing the hair for toxins, drugs or metals to generate a timeline or indicate a particular location

• Human and animal hair differ in their cuticle scales.

• Human scales are flattened and narrow – called imbricate

• Rodents and bats have a coronal cuticle – scales that look like a stack of crowns.

• Cats, seals and mink have spinous scales and look like petals

coronal

imbricate

spinous

2. Cortex

• The largest part of the hair shaft in humans.

• The part of hair that contains the melanin (pigment granules) that give hair its color

• Pigment distribution varies among individuals.

• Larger pigment granules give the cortex an uneven distribution of color when viewed microscopically.

3. Medulla• This is the center of the hair.• It can be a hollow tube• It can be filled with cells• It can be absent• It can be fragmented• It can be continuous• It can be doubled

a. Medullary classifications

1. Continuous: one unbroken line of color

2. Interrupted (intermittent): pigmented line broken at regular intervals

3. Fragmented (segmented): pigmented line unevenly spaced.

4. Solid: pigmented area filling both the medulla and the cortex

5. None (absent): no separate pigmentation in the medulla

C. Types of hair

• Hair varies in shape, length, diameter, texture and color.

• Hair varies from region to region on the body.

• Cross sections of hair can be circular, triangular, irregular or flattened. This influences the curl of the hair.

• Hair can have a coarse or a fine texture.• Because of all these inconsistencies, 50

hairs are usually collected from suspects’ head and 25 pubic hairs are generally collected

• Scientists have identified 6 types of hair on the human body:

• head •underarm •pubic• body (auxiliary)• beard/mustache• eyebrow/eyelash

1. cross-sectional shape

• Head hair: circular or elliptical• Eyebrow/lash: circular with tapered ends• Beard: thick and triangular

• Body: oval or triangular (dependent on regularity of shaving)

• Pubic: oval or triangular

2. Other characteristics• Arm/leg: blunt tip, may be frayed at ends

due to abrasion• Beard: coarse, may have double medulla• Pubic: diameter varies; buckling may be

present

D. Life Cycle of Hair1. Anagen stage: lasts ~1,000 days. 80 – 90% of hair is in this stage

A period of active growth – cells around the follicle are rapidly dividing and depositing materials within the hair

2. Catagen stage: accounts for ~2% of all hair growth and development. Follows anagen as hair grows and changes

3. Telogen stage: ~10 – 18%of all hairs are in this stage. The follicle is dormant or resting.

Hair is easily lost at this time.

E. Treated hair

• Bleaching hair removes pigment, makes hair a yellowish color, brittle and disturbs the scale on the cuticle.

• Artificial bleaching results in a clear demarcation on the hair.

• Bleaching by the sun leaves a more gradual mark.

• Dying hair changes the color of the hair shaft, both the cuticle and the cortex take on the dye color.

• Hair grows at a rate of ~1.3 cm per month.• If hair is color-treated -measuring the length

of the color-treated portion and dividing by 1.3, the length of time since the hair was colored can be calculated.

F. Racial differences

• There are broad characteristics that can be used to differentiate a hair sample as belonging to an individual of a particular race.

• European hair is generally straight or wavy. The pigment granules are small and evenly distributed, the cross-section is oval or round with a moderate diameter with minimal variation. The color may be blond, red, brown or black.

• Asian hair is straight, the pigment granules are densely distributed, the cross-section is round with a large diameter, the shaft tends to be coarse and straight with a thick cuticle and a continuous medulla.

• African hair is kinky, curly or coiled, the pigment granules are densely distributed, clumped and may differ in size and shape; the cross-section is flattened with a moderate to small diameter and considerable variation.

G. Animal vs Human

• In addition to differences in the cuticle, animal hair is distinguished from human hair in its pattern of pigmentation as well as its medullary index.

1. Pigmentation

• In humans, the pigmentation tends to be denser towards the cuticle while in animals it is denser towards the medulla.

• Animal pigments are often found in solid masses called ovoid bodies. Animal hair can change color abruptly in a banding pattern

• Human hair is usually one color along its length

2. Medullary index• This is the ratio of the medulla to the

diameter of the entire hair.• Animal hair has an index of 0.5 or greater• Human hair has an index of 0.33 or less

H. Hair as Evidence

• Hair is collected by plucking, shaking and scraping surfaces. It is also collected by placing tape over a surface to lift any hair that may be present.

• If a large number of hairs are collected from a victim or a crime scene, an investigator will compare the sample with hair taken from the six major body regions of the victim or suspects.

• Hair is viewed macroscopically for length, color and curliness.

• It is viewed microscopically for medullary index, medullary pattern, pigmentation of the cortex and scale pattern.

• Chemicals absorbed by the skin can be found in hair.

• Ingested or absorbed toxins can be detected in hair

• This is accomplished when hair is dissolved in an organic solvent that breaks down the keratin releasing anything that has been incorporated into the hair.

• Using the knowledge of growth rate, time frames can be generated that indicates when substances were ingested or absorbed

Neutron Activation Analysis• This process can be used to

individualize hair:• When hair is bombarded with high-

energy neutrons it releases gamma radiation with different signals

• 14 different elements can be identified within a 2 cm strand of hair…

• The probability of any two individuals having the same concentrations of these elements is one in one million!

DNA and hair• If the hair is forcibly removed, the entire hair follicle may be intact (a follicular tag).

• Blood and tissue will be attached to the follicle and can be analyzed.

• Blood proteins can identify blood type• DNA provides individualized identification• This is not always performed due its

expense…it is usually only done if there is a microscopic match.