They, like many other historical and fictive individuals, are bald, in some cases by their own choice.

他們跟許多歷史和虛構的人物一樣，都是禿頭，有些則是自己選擇要剃光頭髮。

For centuries, a shining dome has been a symbol of intelligence, but despite this, many balding people still wish their hair would return.

好幾世紀以來，光亮的頭頂已成為聰明的象徵，儘管如此，許多禿頭的人們依然希望他們的頭髮可以長回來。

Scientists have long pondered, "Why do some people lose their hair, and how can we bring it back?"

科學家仔細思考很久，「為什麼有些人會掉髮？我們該如何讓頭髮長回來？」

The full-headed among us have about 100,000 to 150,000 hairs on our scalps, and scientists have discovered two things about this dense thicket.

正常人頭皮上的髮量介於 10 萬到 15 萬根之間，科學家已經發現這茂盛叢林的兩件事情。

Firstly, the sprouting hair we see is mostly made up of keratin, the protein leftover from dead cells that are forced upwards as new cells grow beneath them.

第一，我們看到生長中的頭髮大部分都是角蛋白所產生，一種從死掉的細胞殘留下來的蛋白質，被底下新的細胞強迫向上推擠。

Secondly, the structures that drive hair growth are called hair follicles, a network of complex organs that forms before we're born, and grows hair in an everlasting cycle.

第二，驅使頭髮生長的構造稱為毛囊，一個在我們出生之前就形成的複雜網絡器官，讓頭髮生長進入無止盡的循環。

This cycle has three main phases.

這個循環有三個主要階段。

The first is anagen, the growth phase, which up to 90% of your hair follicles are experiencing right now, causing them to push up hair at a rate of one centimeter per month.

第一個是生長期，90% 以上的毛囊正在經歷此階段，讓毛囊以每個月 1 公分的速度向上推擠頭髮。

Anagen can last for two to seven years, depending on your genes.

生長期根據你的基因，可以長達 2 到 7 年。

After this productive period, signals within the skin instruct some follicles to enter a new phase known as catagen, or the regressing stage, causing hair follicles to shrink to a fraction of their original length.

在這生產期之後，皮膚底下的信號下達指令讓部分毛囊開始進入新的階段，也就是退形期，或退化期，導致毛囊從原本的長度些微縮短。

Catagen lasts for about two to three weeks and cuts blood supply to the follicle, creating a club hair, meaning it's ready to be shed.

退形期長達大約 2 到 3 星期，阻斷血液供給毛囊，形成杵状毛，也就是說可以準備脫落了。

Finally, hairs enter telogen, the resting phase, which lasts for ten to twelve weeks, and affects about 5-15% of your scalp follicles.

最後，頭髮進入毛髮休止期，時間長達 10 到 12 週，大約影響 5 至 15% 的頭皮毛囊。

During telogen, up to 200 club hairs can be shed in a day, which is quite normal.

在休止期期間，大約一天 200 根以上的杵状毛會掉落，這是正常現象。

Then, the growth cycle begins anew.

之後生長週期再度開始。

But not all heads are hairy, and, in fact, some of them grow increasingly patchy over time in response to bodily changes.

但並不是每個人都是頭頂茂盛，事實上，因為身體上的變化，有些頭髮隨著時間開始生長不均。

95% of baldness in men can be attributed to male pattern baldness.

95% 禿頭的男人都是雄性禿。

Baldness is inherited, and in people with this condition, follicles become incredibly sensitive to the effects of dihydrotestosterone, a hormonal product made from testosterone.

禿頭可以遺傳，有如此情況的人，毛囊對二氫睪固酮非常敏感，這是一種從睪丸產生的賀爾蒙。

DHT causes shrinkage in these overly sensitive follicles, making hair shorter and wispier.

二氫睪固酮導致敏感的毛囊萎縮，讓頭髮又短又纖細。

But loss isn't sudden.

但掉髮並不是突然發生。

It happens gradually, along a metric known as the Norwood Scale, which describes the severity of hair loss.

而是慢慢地，有一個說明各種掉髮階段的分級法，也就是諾伍德規模。

First, hair recedes along the temples, then hair on the crown begins to thin in a circular pattern.

首先，頭髮延著太陽穴逐漸減少，之後頭頂上的頭髮開始稀疏，形成圓形狀。

At the highest rating on the scale, these balding areas meet and expand dramatically, eventually leaving only a ring of sparse hair around the temples and the back of the head.

達到最高級的規模時，這些禿頭的區塊戲劇性的接合擴展，最後只留下太陽穴以及後腦勺附近稀疏的頭髮。

Genetics isn't all that drives hair loss.

基因並不是掉髮的主因。

Long periods of stress can release signals that shock follicles and force them into the resting phase prematurely.

長期在壓力之下也會釋放信號衝擊毛囊，迫使他們提早進入休止期。

Some women experience this after childbirth.

有些女人在生產後經歷掉髮階段。

Follicles might also lose the ability to go into anagen, the growth phase.

毛囊也可能喪失能力進入生長期。

People going through chemotherapy treatment temporarily experience this.

接受化療的人們也會短暫經歷此階段。

But while balding may look permanent, scientific investigation has revealed the opposite.

即使禿頭看似永久，科學研究發現不一樣的結果。

Below the skin's surface, the roots that give rise to our hair actually remain alive.

在表皮底下，給予我們頭髮生長的根部依然活躍著。

Using this knowledge, scientists have developed drugs that shorten the resting phase, and force follicles into anagen.

透過運用這理論，科學家已經發明藥物可以簡短休止期的時間，強迫毛囊進入生長期。

Other drugs combat male pattern baldness by blocking the conversion of testosterone to DHT so that it doesn't affect those sensitive follicles.

其他藥物透過阻止睪丸激素轉換成二氫睪固酮來對付雄性禿，好讓他們不會影響敏感的毛囊。

Stem cells also play a role in regulating the growth cycle, and so scientists are investigating whether they can manipulate the activity of these cells to encourage follicles to start producing hair again.

幹細胞也是控制生長週期的主要角色，所以科學家正在研究是否可以控制這些細胞的活動，來刺激毛囊開始再次生長頭髮。

And in the meantime, while scientists hone their hair-reviving methods, anyone going bald, or considering baldness, can remember that they're in great company.

與此同時，當科學家不斷尋找讓頭髮再生的方法，任何禿頭的人或擔心禿頭的人，記得你不是孤單一個人。