Perte de cheveux chez l'homme. Quelles en sont les causes ?

The most common type of male pattern baldness is androgenetic alopecia, which accounts for 95% of baldness cases. It can also appear in women with some variations and in a smaller – although not negligible – percentage. Unlike other types of hair loss, androgenetic alopecia is not associated with inflammation or scarring.

Unlike other types of hair loss, androgenetic alopecia is not associated with inflammation or scarring.

Both the onset and progression of the condition is gradual and manifests cyclically with periods of ups and downs, while it consists of both a reduction in the density and quantity of hair.

Initially thinning occurs in the forehead area progressing to the front, top and top of the scalp. The occipital (back) and parietal (side) regions are mostly unaffected.

• An adult has approximately 100,000 to 150,000 hairs which are renewed at a different rate based on the hair growth cycle which includes three phases:

  Ι. Phase of Development or Regeneration (Anagen Phase)

  ΙΙ. Catagen Phase

  IΙΙ.Telogen Phase

  During the first phase which lasts 2 to 6 years the follicles are located deep in the skin producing thick, brightly colored hairs that grow at a constant rate every day. Normally at any given time the largest percentage of hair – about 85%, is in the above phase.

  The second phase is an intermediate stage in which the hair prepares for apoptosis by shrinking the hair follicles. About 1 to 2% of the hair is in this stage which lasts 2 weeks.

  The last phase lasts about 3 to 4 months. Hair stops growing until it eventually falls out.

  Based on the cycle above, a daily loss of 100 to 150 hairs is considered normal. In the event that this is greater and for a prolonged period of time, we can talk about hair loss.

Androgenetic alopecia is caused by a genetically determined increased sensitivity of the hair root to the hormone dihydrotestosterone (DHT) that worsens with aging

We can therefore talk about three main causes associated with this particular type of hair loss, which are considered in combination and not individually.

Genetic predisposition is a strong factor in the occurrence of androgenic alopecia, but it is not absolute that every person who has this predisposition will eventually develop the condition.

Although the exact way in which it is inherited is not known, it is certain that the gene responsible for the occurrence of this type of hair loss is inherited from the mother’s side.

In practice, this means that although the predisposition can be inherited from both parents, this is certain only if there is a history on the mother’s side.

In any case, however, what is certain is that even if a person with a genetic predisposition eventually develops hair loss, the time of occurrence and the rate of progression can vary greatly.

Androgenic alopecia occurs due to the effect of the hormone dihydrotestosterone (DHT), a derivative of testosterone, on hair follicles. As a result of the above action, the duration of the regeneration phase is reduced from 2 – 6 years to months, even weeks.

This leads to the degeneration of hair follicles which gradually shrink resulting in the production of finer, shorter and lighter colored hairs.

It should be noted at this point that it seems that high levels of testosterone or other androgens are not a factor capable of causing hair loss, except in combination with high levels of 5-α reductase – a regulator of DHT production and sensitivity to the effect of androgens, a factor which is inherited.

From the above it becomes clear that the combination of androgens and hereditary predisposition ultimately leads to the appearance of androgenic alopecia.

Naturally, with the process of biological maturation, hairs weaken and hair growth decreases.

Its effect on the creation of hair loss consists in the time during which sensitive hair follicles are exposed to the degenerative action of androgens.

Androgenic alopecia is therefore not a normal result of the aging process which, however, acts catalytically when the two factors coexist.