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.

Hair loss (telogen defluvium)

With the term Telogen Defluvium we mean a modest, not excessive, loss of hair in the telogen phase, but which tends to often be irreversible, with the precise characteristics of hair in decay or involution. The hair that falls out is usually short and fine, with bulbs that are undeveloped and reduced in size.

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Female hair loss

Female hair loss is a common form of non-scarring hair loss, characterized by the progressive loss of hair in the forehead and crown regions, resulting in visible thinning. Unlike male hair loss, female hair loss in the affected areas is usually incomplete and the occipital area is generally spared.

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Cuneiform hair or dwarf hair

This is very short hair, between 1 cm and a maximum of 2 cm in length, which usually has insufficient pigmentation. This hair has a base structure that is quite large, almost like normal hair. It then tends to get smaller towards the end, thus taking on the form of a very pointed cone.
This hair has a strong tendency to fall out.

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Androgenetic alopecia (pattern hair loss) or baldness

Androgenetic alopecia is the most common type of hair loss and affects the majority of white men, with varying degrees of seriousness. It is less frequent in other ethnic groups. Often it can be associated with a family history of baldness, but the absence of other affected family members does not exclude the diagnosis. The condition is characterized by progressive hair loss in the crown area, the front hairline and the temporal area.

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Grey hair

In the trichological field, with the passing of age hair whitening is seen to follow the greying process of the hair on the scalp (called grey hair). Hair becomes grey (white) following a natural biological aging process of the melanocytes, which are the cells tasked with coloring hair.
In the majority of people, the first grey hairs appear around 35/40 years of age in women and around 30/35 in men.

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Hair loss (telogen effluvium)

The term Telogen Effluvium was introduced for the first time by Kligman (*) in 1961 to introduce an acute hair loss of benign origin that follows an intense and short period of stress of different types. Subsequently, Rebora (**) introduced the concept of chronic Telogen Effluvium.

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