What is a hair?

Un cheveu, c’est quoi ?

What is a hair?

Hair (from the hair family) is a long stalk of keratin covered with several layers of scales over most of its surface.

Only the base of the hair, the root, is alive; the rest, the hair shaft, which is the visible part composed of the cuticle, the cortex and the medulla, is biologically dead. This rod is planted in the skin, it is here that the hair grows, at the level of the hair follicle, wrapping the hair like a sheath.

At the bottom of the hair, there is the bulb. It is located in a fatty layer called the hypodermis. It is here that the hair draws its nutritional needs through blood vessels.

There are also nerve endings that signal pain to the brain if you pull your hair too hard.

What is hair made of?

- Beneath the scales is the cortex made up of long keratin cells.

- Keratin cells are composed of small fibers, called MACROFIBRILL.

It is between these MACROFIBRILLE that we find the pigments, which are responsible for the color of your hair.

- MACROFIBRILLS are themselves composed of even smaller fibers called MICROFIBRILLS.

- MICROFIBRILLS are themselves composed of PROTOFIBRILLS.

- Finally, these PROTOFIBRILLES are each composed of 4 strands of keratin twisted two by two.

It is keratin that allows the hair to be both flexible and resistant.

Why can a hair appear more or less soft and shiny?

When light hits a flat surface, it “bounces”. It is said to be reflected in a single direction (called specular).

On the other hand, if the surface is not flat, the light bounces less well or not at all, we say that it is diffused and it is then in all directions.

What our eyes perceive is the return of light which has been reflected or re-scattered on the surface of matter. If light is scattered, less light will reach our eyes.

What covers the surface of the hair are the scales. If the scales are correctly arranged on the surface, in a uniform way and that they are correctly interlocked with each other, they will remain well flattened and the surface will be smooth. Then the light will be correctly reflected.

The result is healthy, smooth and shiny hair.

On the contrary, if the scales are raised or laid out less evenly, then the surface will be less flat. In this case, the light will be diffused instead. Result: the hair will appear duller and coarser.

It is therefore the scales that are largely responsible for the visual appearance of your hair.

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