Hair

The hair has its root at the epidermis level in a kind of containing bag, the hair root, into which the sebaceous gland debouches. Hair cells are reproduced at the hair root level, the only living part of the hair, nourished by the papilla. The formed cells are pushed up by the subsequent reproduction and while moving away from the vital source, they gradually undergo a transformation process, until they become, in the shaft that sticks out of the skin, a structure consisting of keratin, a hardened protein substance.

The shaft is formed by three layers: the outer part, called cuticle, formed by numerous cells laying side by side and overlapping each other like roof tiles or fish scales, acting as a protective barrier. These scales must be closed, so that the hair is stronger and bright.

Under the scalp there is the consistent intermediate layer called cortex, consisting of tapered cells that are very close to each other, which form long fibers containing melanin granules, a substance that determines the characteristic hair color.

Finally there is the inner layer, the thin and cylinder-shaped marrow, formed by round cells and often separated by microscopic air bubbles.

Life Cycle

From a physiological point of view, a hair has an extraordinary long lifetime, as in average it lives 4 years with a growth of 1-2 cm a month. However, not all the hair develops and grows at the same time, because the cells of the hair roots have a cyclic activity characterized by 3 phases: periods of development, defined as Anagen phase, during which we can see the hair growth; periods of relative root involution, defined as Catagen phase, where the growth stops, and ending with rest periods of the hair root cycle defined as Telogen phases which prelude the physiological hair loss and a new Anagen phase of growth.

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