The Study of HairTaylor, 2015PVMHS

Hair evidence What information can be gained from analysis of hair?

Hair alone (without follicle cells) is trace evidence & class evidence. It does not identify a specific individual, but can narrow your

suspects down based of certain characteristics of their hair.

Hair is easily left behind at a crime scene. Adheres easily to carpet, clothes, and many other surfaces

(sheets, blankets, car interior, moist surfaces).

Hair has a tough outer coating and does not decompose easily, so it’s durable.

Hair can be analyzed to determine race, history of drug use, evidence poisoning/toxins, nutritional deficiencies. Hair analysis can sometimes indicate what water supply a

person is using!

History of Hair Analysis

1883: Alfred Swaine Taylor and Thomas Stevenson publish The Principles and Practice of Medical Jurisprudence and include a chapter on using hair in forensic investigations.

1910: Victor Balthazar & Marcell Lambert (French forensic scientists) publish Le Poil de l’Homme et des Animaux (the hair of man and animals) which includes microscopic studies of hair from most mammals.

1934: Dr. Sydney Smith uses a comparison microscope to perform side-by-side analysis of hairs collected from a crime scene.

Today hair analysis includes neutron activation analysis (NAA) , chemical analysis, and DNA analysis

The Function of Hair Why do mammals (including humans) have

hair?

The Function of Hair Helps to regulate body temperature

What happens when you get cold? Why?

Protects the skin against sunlight Skip the “shave” at the dog groomer in summer

Acts as a sensory organ

When hair is very dense,

…it’s called fur.

The Structure of Hair

Hair originates from the skin. Your skin is know as the Integumentary system. Hair is an “accessory organ” to your skin.

The skin has 3 layers: Epidermis (most superficial layer, at the surface) Dermis (middle layer) Hypodermis (deepest layer)

Hair originates from the hair bulb, is surrounded by the hair follicle, and is located in the dermis.

The end of the follicle is called the papilla, this is where the blood vessels meet the hair to supply nutrients.

The Structure of Hair

There is generally a sebaceous gland, aka an oil gland, associated with each hair bulb. Helps water proof the hair and

protect it from drying out.

Also a muscle that attaches to the hair follicle to erect the hair when stimulated (cold or scared).

The hair shaft is what you see (the hair on your arm or on your head).

The Structure of Hair

The cuticle of the hair itself is composed of keratin, which is a protein produced in the skin. Proteins are made up of chains of amino acids that

are connected by strong bonds, making hair strong and flexible.

The hair shaft is made up of 3 layers: the medulla, the cortex, and the outer cuticle. Pencil analogy:

-Central medulla

-Cortex surrounds

medulla

-Cuticle on outside

The Cuticle The outer layer of the hair shaft, made up of keratin.

The scales point away from the scalp. This can indicate where the “younger” part of the hair is

(closest to the scalp). Useful when looking for drugs or toxins at a specific

point in time.

Humans have scales that are flattened and narrow, called imbricate scales.

Some animals have hair with different scales, this allows scientists to distinguish human hair from animal hair. Coronal scales have the appearance of a stack of

crowns. Spinous scales resemble petals.

Imbricate - Human

Spinous - catsCoronal - rodents

The Cortex Contains most of the pigment granules, called

melanin. This gives the hair its color.

Pigment distribution varies from person to person Some people have larger pigment granules, giving

a more uneven distribution when viewed under a microscope.

The Medulla The center of the hair is called the medulla.

There are different patterns that a person could have Continuous Interrupted Fragmented/segmented Solid Absent

There is also significant differences between species.

Medulla patterns

Variation in Hair Shape: hair may be circular, triangular, flattened, or

irregular.

Length

Color: depends on distribution of pigment granules. Human hair is usually one color along the entire length unless it

has been artificially dyed. Animals often have pigments found in solid masses called ovoid

bodies, this is why the color of animal hair can appear banded.

Texture: Vibrissa – the whiskers of many animals Bristle – coarse hair that provides a protective coat Wool – fine hairs that cover the bodies of mammals and protect

from wet & cold

Diameter: The ratio of the diameter of the medulla to the diameter of the hair is called the medullary index. Animals have a greater medullary index than humans.

Human Hair Head and body hair of humans is intermediate

combining the characteristics of bristle and wool.

4 types: Primordial hairs – appears in 3rd month of gestation Lanugo hairs – replaces the primordial hairs,

appears around the 5th month of gestation and are generally shed by the 8th month of gestation.

Vellus hairs – soft hairs spread uniformly all over the body

Terminal hair – found on the scalp, eyebrows/eyelashes, limbs/body, pubic, & axillary regions.

Life Cycle of Hair

Hair proceeds through 3 stages as it develops.

Anagen stage: Period of active growth when cells around the follicle are rapidly dividing. Lasts 2-6 years on the scalp, but may be less on

other areas of the body.

Canagen stage: Period of transition, hair follicle shrinks & papilla detaches

Telogen phase: Follicle remains dormant, eventually hair will loosen and fall out and the anagen stage begins again.

Hair as evidence Review Locard’s exchange principle

Whenever 2 objects come in contact, some transfer of material will occur.

Hair is trace evidence

Hair can be collected by plucking, shaking, placing tape over a surface, using a special vacuum.

If a large number of hairs are collected from a crime scene the technician has to compare the hairs from the crime scene to hairs from the victim and/or suspect.

Hair analysis Can be analyzed macroscopically and microscopically.

Macroscopic analyses include length, color, texture, curliness.

Microscopic analyses include medulla pattern, cortex pigmentation, type of scales on the cuticle, and medullary index.

Many dyes will fluoresce under certain types of light.

Chemical tests can be used to determine presence of toxins or drugs.

If hair is forcibly removed the hair follicle may be present. This is known as a follicular tag. Blood and tissue attached to the tag may be analyzed for

blood type and DNA analysis.

Chemical analysis By testing different parts of the hair it’s

possible to establish a timeline for when exposure to poisons or other toxins occurred.

Hair grows about 1.3 cm per month, so for example if a toxin occurs at 9cm from the root, you would divide by 1.3 to get the approximate time that the exposure occurred.

Neutron Activation Analysis (NAA) can be used to identify up to 14 elements in a single 2cm strand of hair. Including: antimony, argon, bromine, copper,

gold, manganese, silver, sodium, arsenic, chlorine, and zinc

The probability of 2 hairs have the same profile is very low.

Any questions?