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.
CSI Hair Analysis
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.