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遺傳性落髮 HEREDITARY HAIR LOSS

 

隨著遺傳性脫髮(雄激素性落髮/雄性禿),將保有毛髮的毛囊破壞引起落髮。由於遺傳性超敏反應,他們對雄激素睾丸激素反應敏感,因此毛髮生長期相當短。

男性遺傳性脫髮首先在太陽穴上顯現(M型禿),並經常持續頭頂上的禿頂(地中海型禿)。婦女受影響的表現方式大部分會沿著分髮線開始稀疏。

遺傳性脫髮的進展

雄性激素性脫髮(雄性禿)起因為雄性激素濃度及 5-α 還原酶 (5-alpha reductase)。 這種遺傳脫髮的第一個跡象是在青春期之後,常見在20到30歲之間發生。

起初,頭髮沿著髮際線退縮,然後在頭頂上變得越來越稀疏。

有些人,患部會遍及整個整個頭部。然而,很多的人只會保留兩側以及後枕部的頭髮。

然而,在極少數情況下,婦女也會因遺傳原因而失去頭髮(這也是雄性禿)。

所以,發生遺傳性脫髮的女性和男性(雄性禿)並不是因為較高的雄性激素(睪固酮)濃度而引起(雄性禿)。

雄激素脫髮(雄性禿)的一個關鍵因素就是頭髮根源對類固醇激素二氫睾固酮(DHT)特別敏感的反應。

 

各種因素的相互作用

在雄性激素性脫髮(雄性禿)的情況下發生的原因有三個主要的因素所引起:

1. 年齡

正如隨著年齡的增長(老化),生物體的抵抗力一般會降低,頭髮的彈性也會在多年的時間內減少。那些具有遺傳傾向的人也會隨著年齡的增長而損失更多的頭髮。嚴格來說,這不是脫髮,而是減少新毛髮的增長。在老年人身上,男性和女性的體內自身的生長因子,如 IGF-1(胰島素樣生長因子),KGF(角質形成細胞生長因子)和 VEGF(血管內皮生長因子)都會下降。因此,由於缺乏生長因子刺激,因此沒有如年輕時頭髮健康的新陳代謝。

2. 激素

作為身體中的傳遞物質,激素具有許多功能。它們影響毛髮循環的持續時間和毛囊的分裂活性。

即使早在20歲,生長激素 HGH 的生成也就會下降。每十年減少 14%。隨著較少的生長激素的釋放,新髮的結構和密度也相應減少。

年齡相關的脫髮通常只發生在停經後的女性身上,因為雌性激素的減少而產生的掉髮,二氫睾固酮(DHT)對毛囊的破壞作用可能變得突出。因此,除了男人之外,婦女也可能受荷爾蒙脫髮的影響,使原本健康的頭髮看起來越來越細而失去光澤。

雄性激素脫髮(雄性禿)的人,無論是男性還是女性;發生原因都是取決於 DHT (二氫睾固酮),這是身體自身化學變化過程由雄性激素睾固酮形成的。

3. 5-α還原酶 ( 5-alpha reductase )

雄性激素睾固酮通過 5-α 還原酶 ( 5-alpha reductase ) 轉化為二氫睾固酮(DHT)。反過來,具有遺傳性脫髮的人的毛囊對 DHT 非常敏感地反應。 DHT 會損害和削弱髮根。

5-α 還原酶 ( 5-alpha reductase ) 有兩種類型:

5-α 還原酶 ( 5-alpha reductase ) 第I型(5AR1)僅在頭皮前面

5-α 還原酶 ( 5-alpha reductase ) 第II型(5AR2)在整個頭皮

 

如果不積極治療DHT引起的異常落髮,則毛囊會逐漸萎縮,結果也會改變頭髮結構:不再是以前強壯的頭髮,新生長的頭髮會變得細小、無光澤的(細毛)。在顯微鏡下,可以很清楚的看見毛囊萎縮的情況,明顯可見細胞外部萎縮的痕跡。

在對 DHT 具有遺傳性超敏反應的人,毛髮生長期(生長階段)縮短,從而也減少了頭髮的最大可實現生長長度。一個禿頭的男人可能毛囊少於整頭充滿頭髮的男人,但由於縮短的生長階段,使得頭髮幾乎看不見。頭部兩側和後枕區域的頭皮通常對 DHT 較不敏感,因此這些毛髮適合作為因為遺傳性脫髮引起的頭髮移植治療捐贈區。

HEREDITARY HAIR LOSS

 English

Androgenetic alopecia in menwomen
With hereditary hair loss (androgenetic alopecia) the hair follicles which hold the hairs in the scalp are damaged. They respond highly sensitively to the male sex hormone testosterone owing to hereditary hypersensitivity. The hair growth phase is considerably shorter. Hereditary hair loss in men is apparent first at the temples and frequently continues with bald patches on the top of the head. Women who are affected have thinner hair along their parting. 

Progression of hereditary hair loss

Androgenetic alopecia is dependent on male androgen hormone levels. The first signs of this genetic predisposition are visible after puberty, between the ages of 20 and 30. First of all the hair recedes along the hairline, then it becomes increasingly thinner on the top of the head. With some men, baldness spreads over the whole head. However, many people keep their hair at the sides and at the neck.
In rare cases, however, women also lose hair for hereditary reasons. Neither women nor men with congenital hair loss usually display higher testosterone levels, however. A crucial factor for hair loss is rather the fact that the hair roots react particularly sensitively to the steroid hormone dihydrotestosterone (DHT).

The interplay of various factors

In the case of androgenetic alopecia, three factors thus play a major role:

1. Age
Just as resistance of the organism decreases in general as you grow older, the resilience of the hair also reduces over the course of the years. Those with a genetic predisposition also lose more hair as they grow older. Strictly speaking, this isn’t hair loss, but a reduced growth of new hairs. Both in women and men, production of the body’s own growth factors such as IGF-1 (insulin-like growth factor), KGF (keratinocyte growth factor) and VEGF (vascular endothelial growth factor) decreases when you are older. Hairs that have fallen out are therefore not replaced due to a lack of growth stimulation.

2. Hormones
As messenger substances in the body, hormones have numerous functions. They influence the duration of the hair cycle and division activity of the hair follicles.

Even as early as the age of 20, production of the growth hormone HGH decreases. Every ten years production reduces by another 14 per cent. As fewer growth hormones are released, the structure and density of new hair also reduces accordingly.

Age-related hair loss usually only occurs in women after the menopause. Production of female sex hormones reduces and the damaging effect of dihydrotestosterone on the hair follicles can become prominent. Women can therefore also be affected by hormonal hair loss, in addition to men. Previously healthy hairs seem thin and lustless.

People who suffer from hereditary hair loss - whether men or women - have inherited hair root sensitivity to the hormone DHT (dihydrotestosterone), which is formed as a result of the body’s own chemical process from the male sex hormone testosterone.

3. Enzyme 5-alpha reductase
The male sex hormone testosterone is converted into dihydrotestosterone (DHT) by the enzyme 5-alpha reductase. In turn, the hair follicles of people with hereditary hair loss respond extremely sensitively to DHT. DHT damages and weakens the hair roots. There are two types of the enzyme 5-alpha reductase:
5-alpha reductase I (5AR1) only at the front of the scalp
5-alpha reductase II (5AR2) in the entire scalp
If hair loss as a result of DHT is not treated, the hair roots shrink further and further. The hair structure changes as a result, too: instead of the previously strong, full-pigmented hair (terminal hairs), only downy, thin, colourless hairs grow (vellus hair). Under the microscope it is clear how the roots reduce in size until they are a vestige of the outer part of the cell.
In the case of people with hereditary hypersensitivity to DHT, the hair growth phase (anagen phase) shortens and thus also reduces the maximum achievable length of the hair. A bald man may not have fewer hair follicles than a man with a full head of hair, but the hairs are hardly visible due to the shortened growth phase. The scalp on the rear of the head and in the neck area is usually less sensitive to DHT. For this reason, these hairs are suitable, for example, for hair transplants owing to hereditary hair loss.