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Topic 2: The Layers of the Hair
Medulla
Hair
is composed of three principal layers, each with its specific purpose. If
you were to examine a cross section of a hair shaft under a microscope,
you would see the innermost or center portion of the hair shaft, the medulla.
The medulla is also called the pith or marrow of the hair. It is composed
of round cells, two to five rows across. Thick or coarse hair usually
contains a medulla. Fine hair for the most part lacks a medulla, as does
naturally blonde hair. The purpose of the medulla has not yet been determined.
Cortex
The
cortex of the hair is composed of fibrous protein core of elongated cells
that are bonded tightly together. The cortex contains melanin pigment
and is responsible for giving the hair its strength, elasticity and tenacity. It
is responsible for approximately 90 percent of the total weight of the
hair. This is the layer of the hair where chemical changes take place
when changing the color, permanently waving, or relaxing the hair.
Cuticle
The
cuticle of the hair is the outermost layer. It is composed of a transparent,
scale-like single layer of overlapping cells. The function of these
overlapping, shingle-like scales is to protect the cortex. The cuticle
is the protective barrier for the cortex and the medulla. Products
with a high pH cause the cuticle layer to swell and allow liquids to penetrate
into the cortex. Products with a low pH will cause the cuticle to shrink
and harden.
Glossary
of Terms
Cortex
- the second layer of the hair
Cuticle
- the very thin outer layer of the skin or hair
Medulla
- the marrow in the various bone cavities; the pith of the hair
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