• The middle layer: the cortex is the most important and thickest part of the hair shaft. It itself is composed of several layers of pigmented keratin cells that are held together by intercellular cement, which ensures the strong cohesion of the hair cells and the impermeability of the hair. Making up 80% of the hair, the cortex gives it its structure and color.
• The outer layer: the cuticle. The hair is protected by the cuticle, which is made up of protective scales that interlock with each other, like tiles on a roof. They are sheathed by a thin layer of sebum, which ensures the shine of the hair shaft. The scales act as transparent protection and give the hair its shine and silkiness.
The cell renewal of the scalp takes 14 days. However, it can be accelerated in event of inflammation.
The physiological roles of the scalp
The scalp plays 2 major roles.
It houses the hair follicles from which the hair is born and which ensure its growth.
It acts as a real physical protective barrier.
The location of the hair follicles
The scalp differs from the skin of the body in the abundance of hair follicles it contains, the size of the hairs, and the number and volume of sebaceous and sweat glands. It also has a rich nervous and vascular network, which is necessary to supply the substances that are essential for the growth of strong hair.
It is a true reservoir of hair follicles, which are housed in very large quantities in the superficial layer. On average, there are between 100,000 and 150,000.
At the base of the hair follicle is a multitude of small blood vessels called the microcirculation. Their function is to transport blood to the hair bulbs to supply them with nutrients and oxygen, which are essential for the growth of strong, healthy and bouncy hair.
It is this narrow passage that allows the bulb cells, the keratinocytes, to continuously produce the components of the hair fiber.