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.
Šta imaju zajedničko Čarls Darvin, Majkl Džordan i Joda? Poput mnogih drugih istorijskih i stvarnih ličnosti, oni su ćelavi, u nekim slučajevima je to lični izbor. Glava koja se presijava, vekovima je bila simbol inteligencije, ali uprkos ovome, mnogi ćelavi ljudi bi ipak želeli da im se vrati kosa. Naučnici su se dugo pitali, zašto neki ljudi gube kosu i kako se ona može vratiti. Oni među nama sa punom grivom imaju oko 100 000 do 150 0000 dlaka na glavi i naučnici su otkrili dve stvari u vezi sa ovim gustim šipražjem. Prvo, kosa koja niče i koju vidimo većinom se sastoji od keratina, proteina koji ostaje od mrtvih ćelija koje se guraju nagore dok nove ćelije rastu pod njima. Drugo, strukture koje vode rast dlake nazivaju se folikulima kose i predstavljaju mrežu složenih organa koji se formiraju pre našeg rođenja i uz koje kosa raste u neprekidnom ciklusu. Ovaj ciklus ima tri glavne faze. Prva je anagen, faza rasta, kroz koju trenutno prolazi do 90% vaših folikula kose i od koje kosa raste nagore brzinom od jednog centimetra mesečno. Anagen može trajati od dve do sedam godina u zavisnosti od vaših gena. Nakon ovog produktivnog perioda, signali unutar kože navode neke folikule na početak nove faze koja se zove katagen, ili faza regresije, pri čemu se folikuli kose skupljaju na mali deo svoje prvobitne veličine. Katagen traje oko dve do tri nedelje i prekida dovod krvi do folikula, stvarajući mrtvu dlaku koja je spremna da opadne. Konačno, dlaka ulazi u telogen, ili fazu odmaranja, koja traje od deset do dvanaest nedelja i pogađa oko 5 do 15% vaših folikula kože glave. Tokom telogena, i do 200 mrtvih dlaka može da opadne za jedan dan, što je prilično normalno. Ciklus rasta onda počinje iznova. Ali nisu sve glave dlakave, i neke od njih zapravo postaju sve više proćelave tokom vremena kao odgovor na promene u telu. 95% ćelavosti kod muškaraca može se pripisati muškom tipu ćelavosti. Ćelavost je nasledna, i kod ljudi sa ovom boljkom, folikuli postaju izuzetno osetljivi na efekte dihidrotestosterona, hormonskog proizvoda koji nastaje od testosterona. DHT izaziva smanjivanje kod ovih preosetljivih folikula, od čega kosa postaje kraća i pramenastija. Ali gubitak nije iznenadan. Dešava se postepeno, po šablonu poznatom kao Norvudova skala, koja opisuje ozbiljnost gubitka kose. Kosa se prvo povlači kod slepoočnica, a onda počinje da se proređuje kosa na temenu u kružnoj putanji. Na najvišem stupnju skale, ove površine koje ćelave susreću se i dramatično šire, ostavljajući na kraju samo prsten retke kose oko slepoočnica i na zadnjem delu glave. Genetika nije jedina odgovorna za ćelavost. Dugi periodi stresa mogu da pošalju signale koji šokiraju folikule i nateraju ih da pre vremena stupe u fazu odmaranja. Neke žene ovo doživljavaju nakon porođaja. Folikuli takođe mogu izgubiti sposobnost da stupe u fazu rasta, anagen. Ovo se privremeno događa ljudima koji prolaze kroz hemoterapiju. Ali iako ćelavost izgleda trajna, naučna istraživanja su otkrila da je situacija suprotna. Ispod površine kože, koreni iz kojih naša kosa raste zapravo ostaju živi. Koristeći ovo znanje, naučnici su razvili lekove koji skraćuju fazu odmora i folikule teraju u anagen. Drugi lekovi se bore protiv muškog tipa ćelavosti tako što blokiraju prelaz iz testosterona u DHT tako da on ne pogađa te osetljive folikule. Stem ćelije takođe igraju ulogu u upravljanju ciklusom rasta i naučnici istražuju da li uz pomoć njih mogu da manipulišu aktivnošću ovih ćelija kako bi podstakli folikule da ponovo proizvode kosu. U međuvremenu, dok naučnici usavršavaju metode za vraćanje kose u život, svako ko ćelavi ili razmatra tu mogućnost može da se seti da je u sjajnom društvu.