Forensic Science
Name: TEACHER KEY
A. Hair as evidence
a. Human hair is one of the most frequently found pieces of evidence at
the scene of a violent crime. Unfortunately, hair is not the best type
of physical evidence for establishing identity. It is not possible to
show with any certainty that two hairs came from the same person or
animal. However, hair can be used to rule out certain suspects or
scenarios. It can also be used to corroborate (support) other physical
evidence if it is consistent with the rest of the evidence.
b. The average human has approximately 250,000 hairs that get
replaced in a 3 year cycle.
i. About 250 hairs are shed daily; about 100 being from the head.
ii. Blondes tend to have more head hairs then brunettes. Red heads have the least.
c. Hair is considered class evidence. Alone (without follicle cells attached), it cannot be used to identify a
specific individual.
d. In the best case, an investigator can identify a group or class of people who share similar traits who
might share a certain type of hair.
e. Hair can easily be left behind at a crime scene. It can also adhere to clothes, carpets, and many other
surfaces and be transferred to other locations. This is called secondary transfer. Secondary transfer is
particularly common with animal hair.
f. Because of its tough outer coating, hair does not easily decompose.
g. Hair analysis may be helpful to determine the following:
i. Human or animal origin
ii. the broad racial background of an individual
iii. body region from which the hair came
iv. manner in which the hair was removed
v. Chemical tests can provide a history of the use of drugs and other
toxins, indicate the presence of heavy metals, and provide an
assessment of nutritional deficiencies.
vi. When the follicle of a hair is present, DNA evidence may be obtained and it can lead to
individual identification.
h. Collecting hair as evidence
i. Recover all hair present.
ii. Use the fingers or tweezers to pick up visible strands of hair when possible. Tape lift may be
used to help collect hairs if needed. When surfaces are large, they can also be vacuumed.
iii. Place hair in paper bindles or coin envelopes which should then be folded and sealed in larger
envelopes. Label the outer sealed envelope.
iv. If hair is attached, such as in dry blood, or caught in metal or a crack of glass, do not attempt to
remove it but rather leave hair intact on the object. If the object is small, mark it, wrap it, and
seal it in an envelope. If the object is large, wrap the area containing the hair in paper to prevent
loss of hairs during shipment.
B. Function of Hair
a. All mammals have hair. Its main purpose is to regulate body temperature— to keep the body warm by
insulating it.
b. Other functions of hair:
i. decrease friction
ii. to protect against sunlight
iii. sensory
c. In many mammals, hair can be very dense, and it is then referred to as fur.
d. In humans, body hair is mostly reduced; it does not play as large a role in temperature regulation as it
does in other animals. When humans are born, they have about 5 million hair follicles, only 2 percent of
which are on the head. This is the largest number of hair follicles a human will ever have. As a human
ages, the density of hair decreases.
C. Structure of Hair
a. All hair has the same basic structure.
b. A hair consists of two parts: a follicle and a shaft.
i. Follicle is a club-shaped structure in the skin
1. Hair is produced from the follicle. Humans develop hair follicles during fetal
development, and no new follicles are produced after birth.
2. At the end of the follicle is the papilla, a network of blood vessels that supply nutrients
to feed the hair and help it grow.
3. The bulb also contains a sebaceous gland to secrete oil, erector muscles that cause hair
to stand upright, and nerve cells to respond to the environment.
ii. The hair shaft is composed of the protein keratin, which is produced in the skin. Keratin makes
hair both strong and flexible.
1. The hair shaft is made up of three layers:
a. Cuticle- transparent outer layer of the hair; protects the hair.
i. made of scales that overlap one another and point toward the tip end
b. Cortex – middle layer; largest part of the hair shaft, contains pigment granules
i. There are two main pigments found in human hair:
1. Eumelanin- gives color to brown or black hair
2. Pheomelanin- produces the color in blonde or red hair
ii. Small sacs of air called cortical fusi are also found in this region,
especially closer to the root, and tend of be different shapes and sizes.
iii. The cortex provides hair with strength, elasticity and determines the
texture and quality of hair.
c. Medulla- Central core of the hair. It can be a hollow tube, or filled with cells.
i. Forensic investigators classify hair into five different groups depending
on the appearance of the medulla.
ii. Human hairs generally have no medulla or one that is fragmented,
however a continuous medulla is frequently found in the hairs of Native
Americans and Asians.
iii. Animal hairs show a wide variety of medulla patterns.
2. A good analogy for the structure of a hair shaft is
the structure of a pencil
a. medulla being the lead
b. cortex being the wood
c. cuticle being the paint
Good example
of a microscope
drawing of hair:
(however you should
use colored pencil)
D. Differences in Hair
a. Hair can vary in shape, length, diameter, texture, and color.
b. The cross section of the hair may be circular, triangular, irregular, or flattened, influencing the curl of
the hair.
c. The texture of hair can be coarse as it is in whiskers or fine as it is in younger children.
d. Some furs are a mixture as in dog coats, which often have two layers: one fine and one coarse.
e. Hair color varies depending on the distribution of pigment granules and on hair dyes that might have
been used.
f. These attributes can all be used for identification or exclusion in forensic investigations
Hairs “could have a common origin”
Hairs “do not have a common origin”
g. In humans, hair varies from person to person.
h. Different hairs from one location on a person can vary.
i. Not all hairs on someone’s head are exactly the same.
i. Example- a suspect may have a few gray hairs among brown hairs in a sample taken from his
head.
j. Because inconsistencies occur within each body region, 50 hairs are usually collected from a suspect’s
head. Typically, 25 hairs are collected from the pubic region.
i. The recommended method for collecting head hairs is to start by having the person from whom
they are being collected bend over a large sheet of clean paper, rubbing or massaging their
hands through the hair so that loose hair will fall out on the paper. More should then be
gathered by plucking them from representative areas all over the head. A total of 50-100 hairs
are desired. Do not cut the hair.
E. Hair from Different Parts of the Body
a. Hair varies from region to region on the body of the same person.
Female
b. Forensic scientists distinguish six types of hair on the human body:
vs. Male
i. Head hair
ii. Eyebrows and eyelashes
Body
iii. Beard and mustache hair
Hair
iv. Underarm hair
v. Auxiliary or body hair
vi. Pubic hair
c. Each hair type has its own shape and characteristics.
d. Hair from head and pubic region are the most common hairs found at crime scenes.
e. Hair from other animals are also frequently found (pets, farm animals, fur from clothing)
F. The Life Cycle of Hair
a. Hair goes through several stages during its life.
i. Anagen stage
1. Period of active growth when the cells around the follicle are rapidly dividing and
depositing materials
2. Lasts approximately 1,000 days; Approx. 85% of all human hair is in this stage
ii. Catagen stage
1. Transitional or regressive stage that lasts a few weeks; hair growth slows.
2. Accounts for about 2% of all hair growth and development
iii. Telogen stage
1. During this final resting stage, the hair follicle is dormant and hairs are easily lost.
2. About 12% of all hairs are in this stage. Lasts a few months.
b. Distal Tips
i. The appearance of the tip of the hair shaft is an important comparative characteristic.
ii. If sufficient sample is available, it may be possible to identify the type of treatment and estimate
the length of time since the last cutting.
Uncut
Scissors
(freshly cut)
Razor
Clippers
Tip is tapered,
round, split, or
frayed.
Tip is partially
compressed.
Tip has a long
tail on one side
of the cut.
Reveals broken
and partially cut
shafts.
Distal tip
hair shapes
iii. Tips usually take on a rounded form in 2-3 weeks.
G. Treated Hair
a. When a person chemically treats his or her hair, traces of the chemicals used remain. Some of these
changes are subtle and can be detected only by using a microscope.
b. Bleaching hair removes pigment granules and gives hair a yellowish tint. It also makes hair brittle and
can disturb the scales on the cuticle.
c. Artificial bleaching shows a sharp demarcation along the hair, while bleaching from the sun leaves a
more gradual mark.
d. Dyeing hair changes the color of the hair shaft. An experienced forensic examiner can immediately
recognize the color as unnatural. In addition, the cuticle and cortex both take on the color of the dye.
e. If an entire hair is recovered in an investigation, it is possible to estimate when the hair was last colortreated. The region near the root of the hair will be colored naturally.
f. Human hair grows at a rate of about 1.3 cm per month (approximately 0.44 mm per day). Measuring the
length of hair that is naturally colored and dividing by 1.3 cm provides an estimate of the number of
months since the hair was colored.
i. For example, if the unbleached root region measured 2.5 cm, then 2.5 cm divided by 1.3 cm per
month equals approximately 1.9 months or about 7 weeks. This information can be used to
identify hairs from different locations as belonging to an individual.
H. Racial Differences
a. Broad racial categorization can be made by identifying certain characteristics of hair.
I.
Animal Hair and Human Hair
a. Human hair differs from that of other animals.
b. One of the more reliable ways to distinguish between a human and other animal hair is to calculate the
medullary index of the hair.
i. Diameter of the medulla divided by the diameter of the entire hair is known as the medullary
index. If the medullary index is 0.5 or greater, the hair came from an animal. If the medullary
index is 0.33 or less, the hair is from a human.
c. Characteristics of the cuticle may be important in distinguishing between hairs of different species.
i. Cuticle scales differ between species of animals; three basic scale structures include:
coronal (crown-like)

Found in hairs of very fine diameter
and resemble a stack of paper cups
 Coronal scales are commonly found in
the hairs of small rodents and bats but
rarely in human hairs
J. Microscopy
Imbricate (flattened)


Overlapping scales
with narrow margins
They are commonly
found in human hairs
and many animal hairs
Spinous (petal-like)



Triangular in shape and protrude
from the hair shaft
Found on the fur hairs of mink, seals,
cats, and some other animals.
They are never found in human hairs
a. Hair viewed for forensic investigations is studied both macroscopically and microscopically.
i. Length, color, and curliness are macroscopic characteristics.
ii. Microscopic characteristics include the pattern of the medulla, pigmentation of the cortex, and
types of scales on the cuticle.
b. Different kinds of microscopes provide different kinds of evidence.
i. Comparison microscopes are especially important tools to
the forensic investigation of hair.
ii. A fluorescence microscope is equipped with filters to detect
fluoresced light, indicating the presence of a dye or other
treatment.
iii. Electron microscopes provide incredible detail of the surface
or interior of the sample, magnifying the object 50,000 times
or more.
K. Testing for Substances in the Hair Shaft
a. Because hair grows out of the skin, chemicals that the skin absorbs and some toxins and drugs which an
individual ingests can leave traces in the hair.
b. In order to test hair, it must first be dissolved in an organic solvent that breaks down the keratin and
releases any substances that have been incorporated into the hair. A forensic chemist can then perform
chemical tests for the presence of various substances to provide evidence of poisoning or drug use.
c. Investigators can calculate the length of time during which a person was taking drugs or ingesting other
toxins by testing different parts of the hair.
d. Neutron activation analysis (NAA) is another useful technique that can identify up to 14 different
elements in a single two-centimeter-long strand of human hair. The probability of the hairs of two
individuals having the same concentration of these different elements is about one in a million.
L. Testing the Hair Follicle
a. If hair is forcibly removed from a victim or suspect, the entire hair follicle (called a follicular tag) may be
present. If so, blood and tissue attached to the follicle may be analyzed for blood type and DNA.
b. DNA analysis of the hair follicle provides identification with a high degree of confidence, whereas
analysis of the hair shaft usually provides class evidence only.