The hair shaft, like the epidermis, is composed of cells filled with keratin and is lubricated with an oily substance (sebum) secreted by the sebaceous glands that open into the follicle.
The part of the hair emerging from the skin surface is called the hair shaft and the part within the skin is called the hair root.
The center of the hair bulb is immaginated to form the dermal papilla which is both vascularized and contains nerves. Nutrients from the food, and oxigen are absorbed by the derma papilla for generation and growth hair. The cells of the hair in contact with the dermal papilla are called the hair matrix and are responsible for the actual production of the hair.
In other words, the hair matrix absorbs nutrients and oxigen from the blood capillary entering the dermal papilla and forms hair by repeated cell division. At this level has to act all the hair lotion to have effectiveness.
The hair matrix also contain melanocytes that determine the color of the hair, by the production of these pigments is genetically controlled. Apart from albinos, all normal subjects have melanin hair pigmentation, whatever the color. The actual shade of color in each or individual depends not only on which melanin is present but also its quantity and the site, number and shape of pigment granules in the hair cortex. Melanin is throught to acts as an energy sink and free radical scavenger, preventing the transport of deleterious species into the keratin matrix.
A hair originates from a group of cells in the epidermis which penetrate the dermis to form the hair bulb. These cells multiply and move into the inside of the hair follicle. Then, pushing their way to the surface, they get keratinized.
What is keratinization?
Keratinization is a metabolic process which causes the cell to loose its nucleus, that is to die, and to become rich in keratin. Keratin is a very hard, resistant protein existing also in the nails and, to a lesser extent, in the cells of the horny layer. Thus, the entire hair, except for the bulb, consists of dead cells. Upon sectioning the shaft of a hair, the following three parts can be distinguished from within it:
From the point of view of hair beauty, the cuticle with its flakes plays a major role.
When intact, the cuticle makes the hair shiny and pleasantly-
In fact, if the cuticle's flakes are flat and regularly arranged, the hair appears shiny and healthy. Conversely, if the cuticle's flakes are "detached", partly damaged or unevenly "worn", the hair is dull, stiff and tends to stick together. The cortex, located at an intermediate position, is the thickest layer in a hair. It consists of bands of keratin cells and pigment granules, which give the hair its colour. This is the layer on which the chemical treatments changing the hair's colour and waviness act and on which the suplhurated amino acids making the hair strong and soft accumulate.
The medulla, the innermost layer, consists of cells arranged in highly regular rows. These cells too contain keratin filaments and pigment granules. In very thin, soft and weak hair this layer either is very thin or may be absent.