Cuticle: The scales of the cuticle may vary in how many there are per unit of measure, how
much they overlap, their overall shape, and how much they protrude from the surface. The
thickness of the cuticle may vary as well, and the cuticles of some species' hairs may contain
pigment. Characteristics of the cuticle may be important in distinguishing between hairs of
different species but are often not useful in distinguishing between different people.
Medulla: The medulla may vary in thickness, continuity (one continuous structure or broken
into pieces), and opacity (how much light is able to pass through it). It may also be absent. Like
the cuticle, the medulla can be important for distinguishing between hairs of different species,
but often does not lend much important information to the differentiation between hairs from
Cortex: The cortex varies in thickness, texture, and color and distribution of pigments. The
cortex is perhaps the most important component in determining from which individual a
human hair may have come.
Microscopic examination can also reveal the condition and shape of the root and tip.
III. The Biology of Hair
Hair is an outgrowth of the skin and is produced from a structure called the hair follicle.
Humans develop hair follicles during fetal development, and no new follicles are produced after
birth. Hair is composed of the protein keratin. Keratin is also the primary component of finger
and toe nails.
Hair color is mostly the result of pigments -- chemical compounds which reflect certain
wavelengths of visible light. There are two main pigments found in human hair, eumelanin,
which gives color to brown or black hair and pheomelanin, which produces the color in blonde
or red hair. Hair color may also be influenced by the optical effects of light reflecting and
bouncing off the surfaces of the different hair layers.