Structure and composition of the hair

The anatomy of the scalp

Hair grows from the follicle. This is located at the junction of the deep dermis and the hypodermis and is called the bulb.

The blood supply is ensured by a small vessel that penetrates the hair shaft, providing the hair with all the vital elements it needs to be healthy, such as amino acids, minerals and vitamins.

Glands surround the hair shaft, the most important of which is the sebaceous gland which produces sebum, the hair's natural lubricant.

On the surface of the scalp, the pores evacuate the sweat produced by the sweat glands

Structure of the hair

Hair is composed of 95% keratin, a fibrous and helical protein (in the shape of a helix), which is part of the composition of the skin and of all the phanera (hair, nails, etc.).

Synthesized by keratinocytes, keratin is insoluble in water, thus ensuring waterproofing and protection for hair.

18 amino acids are involved in the composition of hair, such as proline, threonine, leucine or arginine, keratin is particularly rich in cysteine (variety of sulfur amino acid) which form disulfide bridges between molecules, giving its rigidity and strength to the whole

The hair structure is divided into 3 distinct parts:

- the pith (or medula): central part of the shaft, it is composed of an amorphous, soft and greasy substance.

- the cuticle: a thin, protective outer layer that contains the nourishing part essential to the development of the hair, highly keratinized, composed of scale-like cells that overlap one another, these are about 60 micrometers long and 6 micrometers wide.

- the cortex: the main component of the hair, where we find long chains of keratin that give the hair its elasticity, flexibility and resistance. The cells of the cortex are linked together by an intercellular cement rich in lipids and proteins. Each cell is made up of bundles oriented in the direction of the length of the hair: these are the macrofibrils, which are themselves made up of microfibrils, which in turn are made up of protofibrils.

The role of melanocytes and keratinocytes

The hair cortex also contains melanin. Produced by specialized cells called melanocytes, melanin is the pigment responsible for hair color.

Located near the hair bulb, melanocytes inject their pigments into the keratinocytes of the developing hair shaft.

The color thus lasts throughout the hair cycle from its genesis to its end, when the hair falls out