Hair and Growth Cycle



  • Epidermis
    It is he surface layer (basal, spinous, granular and corneum) consists of keratinocytes, cells that produce keratin with protective function
  • Dermis
    It isa a layer rich in blood vessels, which carry nourishment to the hair and ensure the health of the scalp. In it there are the bulbs and sebaceous glands
  • Hypodermis scalp (or scalp)
    It is rich in adipocytes with the function of the biosynthesis of fats, protection and thermal isolation. Here are grafted hair follicles. This layer lying on the epicranic muscle whose contracting moves forward and makes the scalp frown.


The hair grows from the hair follicle housed in the hypodermis, and for this reason the distance between the point of emergence of the hair on the scalp and the hair can be up to a centimeter. The sebaceous gland, instead, engages in the hair follicle in the dermis, near the epidermis and close to the surface of the scalp. The union of the hair follicle with sebaceous gland creates pilosebaceous apparatus.
Healthy hair and naturally developed are composed of three parts:

  • Drum or stem – It is the outer part to the follicle, visible on the scalp, is also the dead part of the hair, formed from totally keratinized cells which have lost their vital functions, but have acquired resistance thanks to the high concentration of the exceptionally strong protein fibrous, the keratin
  • Root – It is the inner part of the follicle, not visible because it is immersed in the skin of the hair down to the dermis. It is the living part of the hair, which ensures the growth and renewal
  • Hair bulb – It is located in greater depth than the root, in the lower portion of the hair follicle, where the dermal papilla engages, rich in nerve endings and blood vessels, which gives rise to a matrix of germ cells that, reproducing, push up those previously generated. It is during the ascent of the cells towards the skin that occurs keratinization process that stiffens the hair, leads it to death giving rise to the stem

Chemistry of the hair

The analysis by mineralogramma shows that hair consist mainly of keratin and, to a lesser extent, of other three substances: melanin, lipids and minerals.

Hair growth cycle

The cycle of hair growth and regrowth is a physiological process through which the hair is renewed. In fact, during the life of a human being every hair on the scalp repeats its growth cycle many times: born, grows, dies, and reborn. For this reason, the loss of hair daily should be considered physiologic, and should always be proportionate to the particular characteristics of each one and it is influenced by many factors such as seasonality, genetic and hormonal balance.
The cycle of hair growth (or life cycle) consists of 3 phases:
Anagen Phase – Active growth phase (2-6 years)

It is the growth phase of the hair. It lasts from 2 to 4 years in man, and from 5 to 6 years in woman. In healthy hair approximately 85 to 90% of hair is in this phase. The anagen phase is an active phase because the hair never stops growing. In this phase the bulb has a very intense metabolic activity of nourishment and growth. Moreover the dermal papilla is inserted in the fundamental matrix of the hair, directly in contact with the nerve endings and blood capillaries of the dermis that provide oxygen and nutrients to the hair, supporting their rapid regrowth.

Catagen phase – Transition phase (1-2-weeks)

It is the phase of progressive suspension of vital functions of the hair. It lasts about 1-3 weeks, during which time the bulb goes up to the collar and loses its inner epithelial sheath.
The catagen phase is characterized by a rapid decrease of the cell division (mitosis), until its complete stop when the bulb detaches itself slightly from the follicle up towards the surface of the dermis. During the catagen phase hair growth is much slower and decisive. This phase is easily recognizable as hair begin to show the first signs of undernutrition: thinning of the bulb, in relation to the size of the hair shaft. At the end, the bulb is connected to the dermal papilla through a thin column of cells. Meanwhile, even the melanocytes stop their metabolic activity, while the hair reduces its vital functions until either stop completely.

Telogen phase – Resting phase (2-4 months)

It is the resting phase of the hair. It lasts 2-4 months, during which the hair is still in the hair follicle, but its vital activities are completely stopped. The hair has more oxygen and nutrients from the dermal papilla and remains weakly driven into the follicle. The hair has completed its growth phase, and the root of the hair shows a bulb shaped like a “club”, very thinned and with jagged edges. This bulb has become atrophic, and it looks like the head of a pin at the base of the hair. This situation often alarming patients who believe they have lost the part of the hair follicle, which instead has remained deeply in the skin of the hair ready, if all goes well, to start the regrowth of the hair, a new anagen phase.

Usually in healthy hair, about 9-14% is in the telogen phase, if this percentage increases to 20% is a small and incipient alopecia, while a percentage of 30% means that you are in the presence of a strong alopecia . It should be noted that usually in children, the percentage of hairs in the telogen phase does not exceed 5%, and that’s why their hair grows abundant.

RSS International Journal of Trichology

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