Introduction • Careful analysis of hair can provide important clues in an investigation. History of Hair Analysis

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Chapter 3

The Study of Hair

Scenario: Neutron Activation Analysis of Hair

• Careful analysis of hair can provide important clues in an investigation.

History of Hair Analysis

• Hair has been gathered as evidence for many years.

• Cases are not solved solely on the basis of hair analysis unless DNA analysis can be performed.

Function of Hair

• Hair has important functions for the mammals, including humans, who have hair.

• These functions include temperature regulation and protection.

Structure of Hair

• All hair has the same basic structure.

• One can compare the internal structure of a hair to that of a graphite pencil.

Types of Cuticles

The cuticle is the outer, protective layer of the hair.

• Cuticles can have different shapes depending upon the species of the mammal involved.

Types of Cortex

• The cortex is the layer between the cuticle and the medulla.

Types of Medulla

• The medulla is the center layer of the hair.

• The medulla contains pigment and may be continuous or broken in different patterns.

Types of Hair

• Although all hair has the same basic structure, differences exist between individuals.

Hair from Different Parts of the Body

• Hair that grows on one part of the human body is different from hair grown on another part of the body.

The Life Cycle of Hair

• Hair goes through several stages during its life.

• These stages are called the life cycle of hair.

Treated Hair

• When a person chemically treats his or her hair, traces of the chemicals used remain.

• These traces are not only color or structural changes but also subtle changes

that can be detected only by using a microscope.

Racial Differences

• Broad racial categorization can be made by identifying certain characteristics of hair.

Animal Hair and Human Hair

• Human hair differs from that of other animals.

• One of the more reliable ways to distinguish between a human and other animal hair is to calculate the medullary index of the hair.

Using Hair in an Investigation

• Hair can be used in an investigation.

• Investigators often make observations about the macroscopic and microscopic features of a hair.


• Microscopes (especially comparison microscopes) are important tools to the forensic investigation of hair.

• Different kinds of microscopes provide different kinds of evidence.

Testing for Substances in the Hair Shaft

• Some toxins and drugs which an individual has ingested leave traces in the hair.

• Investigators can calculate the length of time during which a person was taking drugs or ingesting other toxins.

Testing the Hair Follicle

• The hair follicle may contain DNA.

• When DNA is present, hair can be used as individual evidence since a DNA fingerprint can be obtained.

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