Keaton Osborn

Basic Structure

Origins of Hair

By week 22, a developing fetus has all of its hair follicles formed. At this stage of life there are about 5 million hair follicles on the body. There are a total of one million on the head, with one hundred thousand of those follicles residing on the scalp. This is the largest number of hair follicles a human will ever have, since we do not generate new hair follicles anytime during the course of our lives.

Most people will notice that the density of scalp hair is reduced as they grow from childhood to adulthood. The reason: Our scalps expand as we grow.

Medullary Index

Hair is chemically stable especially when compared to other physiological materials such as blood, semen, or any other body fluid. Because hair is strongly resistant from decomposition, its property makes hair a nearly ideal type of physical evidence. As you can see in the figures on the both side, a strand of hair has three layers: cuticle, cortex, and medulla. The outermost covering, cuticle consists of hard overlapping scales that point toward tips end. The cortex contains pigment granules that give hair its color. The medulla is a hollow tube within the hair, which may be present or absent. Depending on the hair, this hollow tube is continuous, or fragmented. The examiner compares above factors: color coarseness, granule distribution, hair diameter, and presence or absence of a medulla.

CSI Hair Analysis

Three layers of the hair shaft are used in determining how a crime was committed and who the criminal may be. The medulla, the innermost core of the hair, can be used to determine the race or ethnicity of the potential perpetrator.

The cortex is the layer over the medulla and is used to compare one hair to another. Microscopic air bubbles and pigment granules help scientists distinguish between the hair types. The outermost layer, the cuticle, can be used to determine the species (if the hair belongs to an animal) through analysis of the patterns of scales that cover the cortex.

The root is used to tell if the hair shed naturally, was pulled out, or cut off. The root is also where DNA can be found.

Britain's CSI School - Hair and Fibre - The One Show