很多偉人都是禿頂，要麼是自然脫髮，要麼是自己剃光。那為什麼有些人會脫髮？又如何讓頭髮長回來呢？
實際上，我們的毛囊與皮脂腺對於雄性激素是非常敏感的。皮脂腺受到雄性激素的影響就會變得肥大，分泌出大量油脂，就造成了我們常說的「脂溢性脫髮」。
一般來說，前額、頭頂的毛囊對雙氫睪酮的受體活性會比較高，會優先與雙氫睪酮結合，然後就優先陣亡了，雄性激素脫髮與基因遺傳有關，而女性脫髮往往是因為壓力等後天因素。
視頻來源：騰訊
中英文字幕
What do Charles Darwin, Michael Jordan, and Yoda have in common? They, like many other historical and fictive individuals, are bald, in some cases by their own choice. For centuries, a shining dome has been a symbol of intelligence, but despite this, many balding people still wish their hair would return.
查爾斯·達爾文、麥可·喬丹和尤達有什麼共同點？ 他們就像許許多多歷史人物和 虛構人物一樣——都禿頂， 有的時候是他們自己選擇要禿頂的。 從古至今，閃亮的圓頭頂都是智慧的象徵， 但是儘管如此， 很多禿頂的人還是希望他們的頭髮還能長回來。
Scientists have long pondered, "Why do some people lose their hair, and how can we bring it back?" 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.
科學家們思考良久， 「為什麼有些人脫髮， 我們又能怎樣再讓頭髮長出來呢？」長滿頭髮的人的頭皮上大概有10萬到15萬根頭髮， 對於這片厚厚的灌木叢， 科學家有了兩個新發現。
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. 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.
首先，我們看到的長出的頭髮中 有很大一部分是由角質組成的。 角質就是因為新細胞在它們之下生長而被向上推的 死細胞中剩餘的蛋白質。其次， 使頭發生長的結構叫發囊。 發囊是複雜器官組成的一個網絡 它在我們出生之前就形成了， 並且使頭髮不斷生長。
This cycle has three main phases. 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. Anagen can last for two to seven years, depending on your genes.
這個周期有3個階段， 第一個階段是毛髮生長初期，即生長階段。 多達90%的發囊正處於毛髮生長初期， 使他們以每月1釐米的速度把頭髮向上推。 根據基因的不同， 毛髮生長初期可以持續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. 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.
在這段高產時期之後， 皮膚裡的信號命令一些發囊進入一個新的階段。 這個階段叫做毛髮生長中期， 或者倒退期。 倒退期使發囊縮小至他們原來長度的一小段， 這個階段持續2到3周， 並且切斷毛囊的供血，使其形成一個杵狀毛， 這意味著頭髮已經準備好要脫落了。
Finally, hairs enter telogen, the resting phase, which lasts for ten to twelve weeks, and affects about 5-15% of your scalp follicles. During telogen, up to 200 club hairs can be shed in a day, which is quite normal. Then, the growth cycle begins anew.
最後，頭髮進入毛髮生長終期，即休止期， 休止期持續10至12周， 並且影響到你5%到15%的頭皮毛囊。 在毛髮生長終期， 多達200根杵狀毛會在一天之內脫落， 這是十分正常的。 然後，生長周期又重新開始。
But not all heads are hairy, and, in fact, some of them grow increasingly patchy over time in response to bodily changes. 95% of baldness in men can be attributed to male pattern baldness. Baldness is inherited, and in people with this condition, follicles become incredibly sensitive to the effects of dihydrotestosterone, a hormonal product made from testosterone.
但是， 不是所有的頭都是長滿頭髮的， 實際上， 隨著時間的推移， 有些人逐漸長出了斑狀 這是對身體變化做出的反應。 男性中95%的脫髮是由於男性型禿。 禿頂是遺傳的， 有男性型禿的人， 他們的發囊會變得對 二氫睪酮 異常敏感， 二氫睪酮 是從睪酮中產生的激素。
DHT causes shrinkage in these overly sensitive follicles, making hair shorter and wispier. But loss isn't sudden. It happens gradually, along a metric known as the Norwood Scale, which describes the severity of hair loss. First, hair recedes along the temples, then hair on the crown begins to thin in a circular pattern.
二氫睪酮（DHT）導致這些過於敏感的毛囊縮小， 使頭髮變得又短又細。 但是脫髮不是忽然發生的。它根據一個度量標準逐漸發生， 這個度量叫諾伍德分型， 它描述脫髮的嚴重程度。 首先，頭髮沿著太陽穴脫落， 然後， 頭頂上的頭髮一圈一圈地變稀疏。
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. Genetics isn't all that drives hair loss. Long periods of stress can release signals that shock follicles and force them into the resting phase prematurely.
在這個分型的最高級， 這些禿頂的部分相互連接然後大幅擴張， 最後只剩下太陽穴周邊一圈稀少的頭髮， 和後腦勺的頭髮。基因不是導致脫髮的唯一原因。 長期的壓力會釋放刺激毛囊的信號， 並且使他們提早進入休止期。
Some women experience this after childbirth. Follicles might also lose the ability to go into anagen, the growth phase. People going through chemotherapy treatment temporarily experience this. But while balding may look permanent, scientific investigation has revealed the opposite.
一些產後婦女會經歷這個階段。 發囊也有可能失去能力， 無法進入毛髮生長初期，即生長期。 接受化療的人會暫時經歷這個階段。 但是，脫髮也許看起來是永久性的， 科學研究揭示了與其相悖的一面。
Below the skin's surface, the roots that give rise to our hair actually remain alive. Using this knowledge, scientists have developed drugs that shorten the resting phase, and force follicles into anagen.
在表皮下， 使我們頭發生長的髮根實際上保持著活性。 運用這個知識， 科學家們發明了可以縮短休止期的藥物， 從而迫使發囊進入毛髮生長初期。
Other drugs combat male pattern baldness by blocking the conversion of testosterone to DHT so that it doesn't affect those sensitive follicles. 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.
其他治療男性型禿頂的藥物， 通過限制睪酮轉變成二氫睪酮的方法來實現 這樣，敏感的發囊就不會受到影響。幹細胞也起到調整生長周期的作用， 所以，科學家們正在研究他們 是否可以控制這些細胞的活動， 從而促使這些毛囊從新開始長出頭髮。
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.
同時， 當科學家在研究頭髮再生的方法時， 禿頂的人或者正在考慮剃光頭的人， 可以記得他們有那些聰明禿頂的人相伴。
視頻、演講稿均來源於TED官網