Hair and Fibers

Hair Morphology

The most basic components of hair are keratin, a very strong protein that is resistant to decomposition, and melanin, a pigment.

The keratins form groups that interact and interconnect to form very stable fibrils. It is this property of hair that makes it such a prime example of physical evidence.

Hair is produced from a structure called the hair follicle. Humans develop hair follicles during fetal development, and no new follicles are produced after birth.

The Function and The Function and Structure of Hair Structure of Hair

Hair on mammals helps to regulate body temperature, decrease friction, and protect against sunlight.

Hair consists of (a) a hair shaft produced by (b) a follicle embedded in the skin.

A hair has three layers (illustrated above): the inner medulla, the cortex, and the outer cuticle.

Types of Cuticle and Cortex

The Outer 2 Layers

The Cuticle is the outermost layer made of over-lapping scales that protect the inner layers of the hair. The Cortex is the thickest layer containing most of the pigment giving hair its color. The distribution of pigment in the cortex

varies from person to person. Pigment, commonly, is denser nearer the

cuticle.

Hair Cuticle

The cuticle is a translucent outer layer of the hair shaft consisting of scales that cover the shaft. Cuticular scales always point from the proximal or root end of the hair to the distal or tip end of the hair.

Types of Medulla

The medulla (the inner section) can be hollow or filled, absent, fragmented, continuous, doubled, pigmented, or un- pigmented.

Medulla

The medulla is a central core of cells that may be present in the hair. Human

Animal

Deer

Types of HairTypes of Hair

Buckled Blunt Double Medulla The cross section of a hair can be circular, triangular,

irregular, or flattened influencing the curl of the hair. The texture of a hair can be coarse or fine. Different regions of the body on which hair can vary

are (1) head, (2) eyebrows and lashes, (3) mustache and beard, (4) underarms, (5) overall body (auxiliary hair), and (6) pubic.

The Life Cycle of Hair

Hair proceeds through 3 stages as it develops:

1. During the long anagen stage, hair actively grows. The cells around the follicle rapidly divide and deposit materials in the hair.

2. In the catagen stage, the hair grows and changes.

3. Hair is in the telogen stage when the follicle becomes dormant. During this stage, hairs easily can be lost.

Growth Cycles of Hair

Anagen – Growing phase– Average growth about 2” per month– 90% of hair is growing at one time– Grows for a period of 2-6 years– Duration of hair life affected by gender, age, type of

hair, heredity, nutrition, & health

Growth Cycles of Hair

– Scalp hairs grows faster on women than men.– Grows faster between 15-30 and slows sharply after age 50

Catagen – Transition phase– Ends the growth phase and lasts only one to two weeks– Follicle canal shrinks & detaches from the dermal papilla– Hair bulb disappears and the shrunken root end forms a

rounded bulb– Less than 1% of the scalp hair is in the catagen phase at any

one time

Growth Cycles of Hair

Telogen – Resting phase– After catagen, the follicle begins a three to six

month phase of resting– About 10% of hair is in telogen phase at one time– After telogen, the cycle begins again– Entire growth cycle repeats itself every four to five

years

Electronmicrograph showing new hairs emerging from the hair follicles of the scalp

Treated Hair

Forensic investigators sometimes can link hair from a location with an individual. – Bleaching disturbs the scales on the cuticle and removes

pigment leaving hair brittle and a yellowish color.– Dyeing colors the cuticle and the cortex of the hair shaft.

Because of this and because hair grows daily, a person’s treated hairs will have specific char- acteristics in common with her or his lost hairs.

Slight Lifting Normal cuticle

Racial Differences

Hair examiners have identified some physical characteristics that generally can be associated with broad, racial groups.

These characteristics, however, will not apply to all individuals in these groups.

In addition, at times, it will be impossible to assign specific hairs to any of these groups be-cause their characteristics are poorly defined or hard to measure.

Caucasian

African-American

Mongoloid

Animal Hair and Human Hair

Core: the medulla -- Thickest layer: the cortex -- Outermost: the cuticle

Pigmentation in animal hair is denser toward the medulla. In Humans it tends to be denser toward the cuticle. Unlike human hair, animal hair abruptly can change colors in banded patterns.

The medullary index is different. In animals the medulla is much thicker than it is in humans.

Animal Hair and Human Hair

Spinous Coronal ImbricateThe outermost layer of the hair shaft (the cuticle), is typically different in animals and humans. – The cuticle scales in animals tend to resemble petals

(spinous) or they give the appearance of a stack of crowns (coronal).

– The cuticle scales in humans commonly are flattened and narrow (imbricate).

Bat Hair and Mink Hair

Human Hair

The imbricate or flattened scales type consists of overlapping scales with narrow margins.

They are commonly found in human hairs

Using Hair in an Using Hair in an Investigation Investigation

Macroscopic investigation can indicate length, color, and curliness.

Microscopic investigation can indicate fine detail in hair structure. – Phase contrast microscopy, for example, can show

the presence of dye or other treatments. – Electron microscopes can provide more detail of the

surface or interior of the sample. In the sample above, note the overlapping scales and the pigment granules in the cortex.

Hair Forensics: Collection

Hairs can be recovered from items using a number of different techniques.

Some of the methods used to collect hairs from clothing and bedding items are scraping, shaking, taping, and picking.

Debris from large carpeted surfaces might be vacuumed into a filtered canister.

If the specific location of a hair on a clothing item is important, it might be necessary to pick off the hair or tape the item and record where the hair was removed.

Hair Forensics: Which Hairs?

Head hairs and pubic hairs exhibit a greater range of microscopic characteristics than other human hairs; therefore, head and pubic hairs are routinely forensically compared.

Twenty-five randomly selected head hairs are generally considered adequate to represent the range of hair characteristics of that individual.

It is recommended that the same number of hairs be collected from the pubic region.

Things to consider when viewing hair

Length: Length is considered, although hairs may have been cut between the time of deposition of the questioned specimen and the collection of a known sample. In addition, there may be a significant difference in the lengths of the shortest and longest hairs on an individual's head.

Tip: The tip can be cut, broken, split, abraded (rounded), or finely pointed as illustrated by An individual's grooming, hygiene, health, and nutrition can affect these features.

Glass-Cut or Broken Hair Tip

Cut Hair Tip

Worn Razor-Cut Tip

Scissor Cut

Razor Cut

Broken Hair

Burned Hair

Testing for Substances in the Hair Shaft

1. Chemicals that the skin absorbs often can be detected by analysis of the hair shaft.

2. A forensic scientist can perform chemical tests for the presence of various substances.

3. The hair shaft can be examined in sections to establish a timeline for exposure to toxins.

4. Neutron Activation Analysis (NAA) can determine concentrations of substances in the sample.

Testing the Hair Follicle

Microscopic assessment of the follicle is performed first because it is cost effective and quick. – If a microscopic match is found, the follicle can

be blood tested and perhaps show the blood type.

– If a microscopic match is found, the follicle can be DNA analyzed to provide identification with a high degree of confidence.

What is this?

LICE

Fiber

Introduction and How Forensic Introduction and How Forensic Scientists Use FibersScientists Use Fibers

Fibers often fall off and are picked up during normal activities.

Very small fibers easily shed from most textiles and can become trace evidence.

In an investigation, collection of fibers within 24 hours is critical.

Fiber evaluation can show such things as the type of fiber, its color, the possibility of violence, location of suspects, and point of origin.

Sampling and Testing Sampling and Testing

Weaving spun fibers (yarns) together produces clothing and many textiles.

Shedding from an article of clothing or a textile is the most common form of fiber transfer.

Natural fibers require only an ordinary microscope to find characteristic shapes and markings.

Infrared spectroscopy can reveal something of the chemical structure of other fibers that, otherwise, may look very much alike.

Sampling Sampling and Testingand Testing

If a large quantity of fibers is found, some can be subjected to destructive tests such as burning them in a flame (see analysis key above) or dissolving them in various liquids.

Crimes can be solved in this way by comparing fibers found on different suspects with those found at the crime scene.

Fiber Classification —Natural Fibers

woven wool textile Animal fibers (made of proteins): Wool from sheep, cashmere and mohair from goats,

angora from rabbits, and hair from alpacas, llamas, and camels are commonly used in textiles.

Shimmering silk from caterpillar cocoons is longer and not as easily shed.

Fiber Classification —Natural Fibers

Plant fibers (made of the polymer cellulose): can absorb water. are insoluble in water. are very resistant to damage from harsh

chemicals. can only be dissolved by strong acids. can be common at crime scenes because

they become brittle over time.

Fiber Classification

—Natural Fibers

Plant fibers: Cotton from seedpods is the plant fiber most

commonly used in textiles (shown above). Coir from coconuts is durable. Hemp, jute, and flax from stems grow in bundles. Manila and sisal from leaves deteriorate more quickly. Mineral Fibers: Fiberglass is a fibrous form of glass. Asbestos is a naturally occurring mineral with a

crystalline structure.

Fiber Classification —Synthetic (artificially produced) Fibers

Until the nineteenth century only plant and animal fibers were used to make clothes and textiles.

Half the products produced today are artificially produced.

Artificially produced fibers include rayon, acetate, nylon, acrylics, and polyesters.

Fiber Classification —Synthetic (artificially produced) Fibers

Regenerated Fibers (derived from cellulose):

Rayon is the most common of this type of fiber. It can imitate natural fibers, but it is stronger.

Celenese® is cellulose chemically combined with acetate and is often found in carpets.

Polyamide nylon is cellulose combined with three acetate units, is breathable, lightweight, and used in performance clothing.

Fiber Classification —Synthetic (artificially produced) Fibers

Synthetic Polymer Fibers: Petroleum is the basis for these fibers, and they have very different characteristics from other fibers. Monomers in large vats are joined together to form polymers. The fibers produced are spun together into yarns.

They have no internal structures, and under magnification they show regular diameters.

Fiber Classification—Synthetic (artificially produced) Fibers

spandex nylon

Examples of synthetic polymer fibers: Polyester—found in “polar fleece,” wrinkle-resistant, and

not easily broken down by light or concentrated acid; added to natural fibers for strength.

Nylon—easily broken down by light and concentrated acid; otherwise similar to polyester.

Acrylic—inexpensive, tends to “ball” easily, and used as an artificial wool or fur.

Olefins—high performance, quick drying, and resistant to wear.

Comparison of Natural and Synthetic Fibers

Visual Diagnostics of Some Common Textile Fibers under Magnification

Yarns, fabrics, and textiles

Fibers can be twisted (spun) into yarn of any length, thick or thin, loose, or tight. A blend can be made to meet different needs such as resistance to wrinkling.

Fibers can be woven into fabrics or textiles. – Threads are arranged side by side (the warp). – More threads (the weft) then are woven back

and forth crosswise in one of a number of different patterns through the warp.

Yarns, fabrics, and textiles

Weave Patterns