Do you know your hair?

Whether long or short, we have always attributed great importance to our hair, considering it an integral part of our style and our idea of beauty. Over the centuries, fashion and taste have evolved, colors and hairstyles have changed from time to time, but hair has always remained the center of our attention. There are many reasons why hair is such an important feature for any culture, to be found in psychology and anthropology. Today we are not going to investigate the mystery of this fascination of ours, but another “mystery”, so to speak, that can be revealed by science: what is hair really made of?
Let’s find out!

We will start by saying that hair is inert matter, this means that it is a non-living skin attachment, therefore it is not able to repair itself and not endowed with its own vital functions. The root of the hair is the living part, it is where the birth of the hair takes place, but the shaft is “dead matter”.

How is hair structured?

The structure of the hair is concentric: let’s imagine it as a very tiny tree trunk. Cutting it longitudinally, we will discover three sections, one inside the other. We will shortly see what they are.

We can divide a hair by its length into two parts, the root and the stem. The root is the active part of the hair, the one that we do not see because it is inserted in the hair follicle on the skin. The terminal part of the root is called the bulb.

The visible part of the hair, the one that we can touch and comb, is called the stem. The structure of the stem seen under the microscope is composed of three concentric layers:

• an outer part called the cuticle, formed by keratin scales overlapping in layers;
• the area under the cuticle is called cortex or cortical area, and it is the one that gives color to the hair, which will be more or less dark according to how much melanin will be contained in it;
• the innermost area, called medullary, whose function is still unclear and it is not even present in all hairs.

Keratin, the substance of the hair

IThe hair is made up almost completely by keratin. It is a protein with a high molecular weight, which makes it very resistant. Contrary to what you might believe, thin hair has thicker outer cuticles than thicker hair. What precisely makes them thinner is the fact that they have a finer cortex. The cortex is the most important part of the hair shaft, it is composed of fusiform cells, which give the hair its elongated shape, rich in keratin and melanin grains, the pigment on which the color of the hair depends. Holding everything together is a matrix composed of lipids and proteins.

Melanin, which, as we said, gives color to the hair, is produced by melanocytes which are located inside the root of the hair, and can be of two types: eumelanin, which produces a brown/black color, or pheomelanin, which produces a yellow/red color. Their combination can create endless shades of hair color.

What about white hair? They are due to the arrest of the melanocytes functioning inside the bulb: they simply cease to produce pigment, and the cortex of the hair remains devoid of color.

How does hair grow?

Hair does not grow continuously, as one might think, but follows a cycle. The period of growth, called anagen, is followed by a period of slowdown, catagen, which is followed by the phase of death and fall of the hair, called telogen. After telogen, a new hair begins to form inside the bulb. Each hair on our head is in a different phase of its life cycle than the neighboring hairs: if this were not the case, we would periodically witness the appearance of empty patches or the simultaneous fall and regrowth of all the hairs.

And finally, a few numbers

A single head is made up of an average of 100,000 to 150,000 hairs. Every day we physiologically lose 50 to 100 hairs.
On average, the rate of hair growth is about 18 cm per year, so if you’re entertaining the idea of cutting your much-desired bangs, or giving in to a nice pixie cut, you can now calculate the time it will take for your hair to return to exactly its current length.