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.
• 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.
• 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.