We do not lose our hair overnight! It is simply that over time, or more prematurely, it grows more finely and in smaller and smaller quantities until it finally disappears.

  A phenomenon with many causes


The progressive loss of hair is called alopecia . Baldness is its ultimate form. The word "alopecia " comes from the Greek "alopex" which means "fox", this animal being liable to lose its fur through a disease. But hair is not fur and alopecia is not in any case a disease!

While the deeper underlying causes of alopecia are still poorly understood, certain phenomena associated with it have been discovered. Thus, a link has been established between the appearance of alopecia and the hair follicle connective tissue sheath becoming rigid. The hardening of this sheath slows the development of the hair follicle during the anagen phase. Thus the hair lacks vigour and thins. Cycle after cycle, the follicle becomes smaller and finally, miniaturised, it only produces a simple down (vellus hair ) ?.

As the phenomenon of alopecia progresses, hairs in the telogen phase are therefore replaced less and less and the proportion of anagen phase hair decreases, causing progressive lowering of hair density.

Whether in a man or a woman, this slow progressive decrease of hair density, frequently starting from about the age of 50, is an absolutely natural phenomenon linked to the ageing process.

However, in men particularly, hair loss can sometimes begin its development much earlier. It involves various factors.

  The hormonal factor
While several hormones seem to control hair growth, it is certain that the male hormones, the androgens , play a primordial role in the appearance of alopecia. These hormones, in particular testosterone, tend in fact to atrophy the hair follicles. We can therefore understand why the premature so called androgen-genetic form of alopecia affects men infinitely more than women: in the latter, the female hormones, the oestrogens , protect the follicle from the action of androgens.
An illustration of this female protection is given by the phenomenon well known to young mothers: the abundant loss of hair several months after giving birth. Rejoicing in the delightful name of effluvium post-partum , this phenomenon is easily explained. During pregnancy the high oestrogen levels in the woman's body prevent the hair from moving into the telogen phase. For 9 months, they remain locked in the growth phase. During the re-establishment of hormonal balance which occurs after giving birth, all these hairs enter the telogen phase which ends 2 or 3 months later by their being shed en masse. The usual cycle then restarts and the head of hair rapidly recovers its ordinary appearance.
In women, it is only after the menopause that a form of diffuse hair loss is likely to occur, due to the sharp decline in oestrogen levels. This alopecia can be avoided by hormone substitution therapy.

Finally, to underline the complexity of hormonal phenomena, it should be pointed out that while androgens hinder the growth of hair, they encourage on the other hand the growth of the beard. Thus areas hardly 10 centimetres apart can show opposite responses to the same hormone.

  The genetic factor
Whether considered through heredity or from the ethnic point of view, genetics play an important role in alopecia.

The fact that fathers and sons are very often bald tends to show that alopecia is genetically programmed. However, the complexity of the phenomenon makes it doubtful whether a specific alopecia gene exists and it seems unlikely that a single gene is the cause. On the other hand, as with the shape of the hair or its speed of growth, the propensity towards alopecia varies depending on the ethnic origin of the individual. As Hamilton showed as early as the 1940s, Asiatic heads of hair are less prone to it than others. On the other hand, despite the relative absence of data concerning African hair, this seems to be on an equal standing with Caucasian hair as regards alopecia. Here again it is an aspect related to genetics even if other considerations, such as nutrition, enter the picture.

  The local factor
Hamilton's diagrams clearly show that different areas of the scalp exhibit different behaviour relative to alopecia. It begins first of all at the sides of the forehead, in the regions known as temporal-frontal gulfs, before reaching the summit of the skull, the vertex . On the other hand, the neck and the temples are extremely resistant and total baldness is extremely rare. Most frequently an appearance like a monk's tonsure occurs; we speak then of "Hippocratic baldness" in honour of Hippocrates who also had this final crown of hair.

  Aggravation factors
Certain factors can have an effect on alopecia, either by encouraging its appearance or by accelerating its progression. Others are the cause of temporary alopecia.
This is the case for chemotherapy. This treatment consists of preventing the proliferation of cancerous cells from the diseased organ. To achieve this, substances are used which block cell division, mitosis , the rate of which is very high in cancerous cells. Hair has the highest rate of mitosis within the human body. As a consequence, it is the first victim of chemotherapy: as its growth is prevented, it falls out in large quantities. On stopping treatment, it grows again and carries on its usual cycle.

Radiotherapy and taking certain drugs can also provoke temporary alopecia which ceases at the end of the treatment.
The same applies to dietary or vitamin deficiencies. The altered head of hair recovers its normal appearance as and when dietary equilibrium is re-established.

Finally, for reasons which are still obscure, stress can sometimes be the origin of a sudden disappearance of hair over an area of several cm2. This phenomenon, called alopecia areata, is generally of short duration and hair grows again spontaneously a few months later.

It can be seen that the numerous factors affecting alopecia makes its study difficult. However, the outlook is optimistic because of new tools available to scientists today.
Thus the Su.Vi.Max epidemiological study has already provided valuable statistical data on the subject. In addition, the perfection of a follicular model is allowing a better understanding of the appearance and evolution of alopecia. Finally, the possibility of making a hair grow in vitro provides a new approach to hair growth.





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