Scientific Area

Life cycle of hair

CATEGORIe AREA scentifica

Scientific collaboration between Professor Marco Toscani and Dr. Pasquale Fino, Chair of Plastic, Reconstructive and Aesthetic Surgery, Umberto I Health Center – “Sapienza” University of Rome.

The life cycle of hair and its subsequent growth occur at a speed of 1-1.5 cm per month. Hair is a living element that follows a follicle cycle with an average duration of 2-6 years. In humans, unlike other mammals that are subject to a periodic change, this cyclic evolution is not synchronous (therefore each hair is independent from the others). A physiological loss of hair up to a maximum of 100 per day is considered normal. Hair grows cyclically following three phases: A growth phase called the anagen phase, a regression phase called the catagen phase and a resting phase called the telogen phase.

Fasi del ciclo del capello
Il ciclo del capello

With regards to the different lengths of the various phases of the hair growth cycle and in normal conditions, hair in the anagen phase represents 80-90% of the total, that in the catagen phase 1% and that in the telogen phase 10-20%.

There are six sub-phases in the anagen phase. The first five sub-phases last for a very short period of time and consist of the proliferative phase, while the sixth phase is the longest, and is characterized by a phase of differentiation. The duration of the anagen phase differs between men and women. It is recognized that for men it usually lasts 2-4 years, while for women 3-6 years.
The catagen phase represents the moment in which the follicle starts to diminish and slowly ceases mitosis. It has a duration of around 7-21 days. It is difficult to find hair in a trichogram during the catagen phase.
The telogen phase is the resting phase of the follicle and lasts about 3 months, during which the follicular sac that contains the hair bulb climbs towards the epidermis. This climb occurs at the cost of the lower segment of the follicle. In this phase, the bulb assumes its typical clubbed aspect due to the retraction of all the follicular sheaths. Once the climb is complete, the bulb is projected externally and upon the first pull (while shampooing or brushing), it leaves the follicular seat, where the anagen cycle for new hair has probably already started.

In humans, the hair cycle of the various follicles of the scalp is more asynchronous compared to that of mammals that undergo a periodic change. Nevertheless, during the course of the year, in humans we can observe two periods in which hair falls out in the telogen phase. This occurs in the spring and more visibly in the fall. This rhythm seems to obey and submit to the various natural cyclic phenomena, such as the length of the day and the change in temperature in the various days of the year.

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The acronym PRPHT stands for “Platelet Rich Plasma Hair Therapy”. It is a therapeutic medical technique that falls within the field of “regenerative medicine”; it is based on the principle that stem cells, which have been demonstrated to be present in the hair bulb, are equipped with growth factor receptors.

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Its volume varies from person to person. This is why some individuals are born with thin hair, while others are born with thick hair.

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Scalp pain and irritation (or trichodynia) are pathological conditions that affect both women (in a greater percentage) and men (in a lower percentage). The pain felt on the scalp, spontaneous or caused by treatment, and in particular around the roots of the hair, may be more or less intense, alternating at times between periods of disappearance, associated with burning, tingling or itching.

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Psychogenic alopecia (psychological baldness)

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Hair types and morphology

Some parameters and characteristics should be taken into consideration when assessing hair types and morphologies: shape, density and appearance. The appearance of hair, in the form of lanugo, occurs during the fourth month of pregnancy.

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