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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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.
達爾文、喬登和尤達有何共通點呢? 就像許多歷史上和小說裡的 人物 -他們都是禿頭的! 少數的案例是自身的抉擇 好幾百年來光滑的禿頂 一直是智慧的象徵 不過儘管如此許多正在禿頭的人 還是希望頭髮會長回來 科學家們已經苦思許久 「為什麼有些人會沒了頭髮? 以及該如何把頭髮長回來?」 一頭茂盛的髮量在頭皮上約有 100,000 到 150,000 根頭髮 而關於這茂密的髮林 科學家們發現了兩件事 首先我們所看到不斷長出的 頭髮主要是由「角蛋白」所構成 從死去的細胞而來的蛋白質剩料 當新細胞在其下方生長時受力向上冒出 第二、驅使頭髮生長的構造叫「毛囊 」 早在我們出生前所形成之 複雜網絡的身體部位 並且在永不止息的循環下長頭髮 這循環有三個主要的階段 第一階段是「生長期」 你們多達 90% 的毛囊 正在歷經這個階段 造成它們將頭髮以每個月 1 公分的速率往上推出 生長期取決於你的基因 能夠持續 2 到 7 年 在這個生意盎然的階段之後 皮膚內的訊息會指示部份毛囊 進入叫做「衰退期」的新階段 造成毛囊萎縮成原先長度的一小部分 衰退期會維持大概 2 至 3 個星期 以及阻斷毛囊的血液供應 產生「杵狀髮」 這表示著它做好準備要被脫落掉了 最後頭髮進入了「休止期」 這會維持 10 至 12 個星期 並且影響到大約 5 到 15% 的頭皮毛囊 在休止期一天能夠脫落 多達 200 根頭髮 這樣是稀鬆平常的事 接著生長循環又重新來過 不過並非每個人的頭全都毛髮茂密 而且事實上有些人長期下來 因應身理上的變化 頭髮長得越來越稀少 男性中 95% 的禿髮可以 被歸成「雄性禿」 禿頭是遺傳的 有這種情形的人身上 毛囊對二氫睪固酮 - DHT 的作用 變得益加敏感的 那是一種從睪固酮素產生的賀爾蒙產物 DHT 導致這些過度敏感的毛囊縮水 使得頭髮更短、更細弱 但是掉髮不是一夕產生的 它依循著諾伍德量表逐步地發生 該量表指出掉髮的嚴重程度 首先、髮線延著太陽穴消退 接著頭頂的頭髮以圓形樣態開始變稀疏 在量表上的最高分級來說 這些光禿的區域驚人地相遇、擴展開 最終只剩下頭頂外圍和後腦稀少的頭髮 基因並不是驅使頭髮消失一切的原因 長期的壓力能夠釋放出打擊毛囊的訊息 並迫使它們永遠地進入休止期 有些婦女在產後會經歷這種狀況 毛囊也可能失去進入生長期的能力 接受化療的人會短暫性地經歷這種情形 但是當禿頭也許看來是改變不了了 科學研究卻呈現出相反的一回事 在皮膚表皮下方長出頭髮的髮根 事實上還持續活著 運用這項知識科學家們 開發出藥物來縮短休止期 並且迫使毛囊進入生長期 其他打擊雄性禿的藥品 透過阻斷睪固酮轉變成 DHT 所以它不會影響到那些敏感的毛囊 幹細胞在管控生長週期上 也扮演了重要的角色 所以科學家們正在研究 到底能否操控幹細胞的活動 來促使毛囊再次啟動長出頭髮嗎? 當科學家還在增益他們的 頭髮回春辦法時 際此同時任何正在禿頭 或是認為是禿頭的人 能記好來「同病相憐者大有人在!」