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: manifestation, causes and prevention

A shedding of hair is considered physiologically normal when hair loss is limited to around one hundred hairs per day. During an individual’s life hair grows, falls out and regrows around twenty times. Each cycle, especially for females, may last up to six years and if hair loss is found within this time frame, it is considered absolutely physiological.

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Sebaceous glands

The sebaceous glands are glands that secrete sebum, an oily, acidic substance with a pH of 3.5. They are connected laterally to the hair follicle. Sebaceous glands are found with a density of approximately 100/cm2 throughout all areas of the skin. In the human body, they are located across the entire surface of the skin, except for the palms of the hands and the soles of the feet.

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Dry hair

Both men and women of any age may have dry hair. This situation is endured not only as an aesthetic problem, but in time may represent a problem concerning hair health. Dry hair often appears weak, fragile and tends to become brittle and to break.
Dry hair often has split ends and other forms of damage to the shaft.

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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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Split ends

The phenomenon of split ends, also called trichoptilosis, is a hair problem that depends on an alteration of the hair shaft with concurrent modification and deterioration of the structure, form and physiology of the hair.

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