- Down a little bit. - OK. - Yeah. Oh, yeah, that's it. Don't stop.

- 下面一點。- 好。對了。喔對，就是這樣。不要停。

Hey, guys, Tara here with an answer to one of life's greatest mysteries: Why is scratching an itch always make it worse?

嗨各位，我是 Tara，今天將要為大家解答一件生活中的奧秘：為什麼我們抓癢時會越抓越癢呢？

Every one of us has been bitten by a mosquito at some point.

我們每個人都一定有被蚊子咬的經驗。

It actually happened to a friend of mine last week,

我的一個朋友就在上週被蚊子咬了，

and he ended up scratching it so hard he created an open wound, the size of a dime which is disgusting.

他抓得太用力，最後變成了一個破皮的大傷口，像一個硬幣一樣大，非常噁心。

But we've all been there, well, some of us.

但我們都有過這樣的經驗，有些人啦。

Most of us get a bug bite, we scratch it for a while and then in a few days it goes way, and we never think about it again.

我們大部分的人被蟲咬後，抓一下，然後過幾天包就會消失，而我們再也不會想起它。

But believe it or not, there are millions of people out there who suffer from chronic itching.

但不論你相不相信，世界上有幾百萬人深受慢性搔癢症所苦。

Conditions like eczema and even cancer or kidney failure can worsen it, and in many cases it can have a serious impact on someone's life.

症狀像是濕疹，癌症或腎衰竭甚至會讓你癢得更嚴重，在許多案例中，癢甚至會影響到一個人的生活。

Well, it boils down to serotonin.

這是因為血清素的關係。

Serotonin is a neurotransmitter that regulates tons of different functions in your body.

血清素是一種神經遞質，負責調節許多身體中不同的功能。

Your mood, your memory, your sleep, your appetite, even blood clotting.

你的情緒、記憶、睡眠、胃口，甚至是凝血功能。

It produces feelings about happiness and well-being but it also controls pain, and that's where the itching part comes in.

血清素也會製造快樂和幸福的感覺，但它同時也控制了痛覺，這也是「癢」的來源。

Chu Fang Chen, as a researcher at Washington University, and he's been conducting studies over the years to see what produces the urge to itch.

華盛頓大學的學者 Chu Fang Chen，已經研究造成癢的原因許多年。

His most recent one involved mice who were genetically engineered to produce no serotonin.

他最新的實驗對象是基因改造的老鼠，牠們體內沒有血清素。

And he found that when those mice were injected with a chemical to induce itching, they had almost no urge to scratch.

他發現當這些老鼠被注射引發搔癢感的化學物時，他們幾乎不會有抓癢的動作。

Meaning that the urge to scratch an itch begins as soon as serotonin leaves your brain and reaches the irritated spot,

這代表一旦血清素離開大腦到達患部，你就會產生抓癢的欲望，

so whenever we scratch an itch we're actually doing so because the pain of scratching temporarily overrides the itchy feeling.

所以我們在抓癢時就是這麼回事因為抓癢造成的疼痛感會覆蓋過癢的感覺。

The problem is that that pain causes your brain to release more serotonin, which intensifies the itch even more.

問題是這種痛覺會讓你的腦釋放更多的血清素， 血清素會加劇你癢的感覺，所以這基本上是個循環。

So it's essentially a feedback loop where you're constantly scratching harder and harder to get rid of the itchy feeling, but all you're doing is really making it even more itchy.

當你一直抓癢，越抓越用力，想要擺脫癢的感覺時，你在做的只是讓它越來越癢。

It make sense but it does bring up another interesting question: Why does serotonin cause an itchy sensation to begin with?

這也引發另一個有趣的問題：為甚麼血清素帶來的感覺會被稱為「癢」呢？

Well, according to Chen, it has to do with GRPR neurons, which are a group of brain cells known to increase itchy sensations.

根據 Chen 的說法，這跟一組腦細胞 GRPR 神經元有關，GRPR 神經元會造成癢的感覺。

A serotonin starts rushing to the part of your body that's irritated,

當血清素開始衝向患部時，

its wires basically get crossed, and it activates those GRPR neurons which intensifies the itch even more.

線路被連接起來，刺激 GRPR 神經元，加劇癢的感覺。

Chen believes that people who suffer from chronic itching could find relief once a therapy is developed to block the receptor that cause the serotonin to activate those neurons.

Chen 相信只要能夠發展出攔阻神經元傳遞血清素到感覺器官的治療方法，長期受癢所苦的人就可以得到解脫。

Until then, the best solution seems to be lots of anti-itching cream and other mittens, the softer the better.

在此之前，最好的治療方法似乎只有抗癢霜、防抓手套，軟一點的更好。

My suggestion, not his.

這是我的建議啦，不是 Chen 的。

What do you guys think? Have you ever scratch the itch so hard that made you bleed?

你們覺得呢？你有沒有因為抓癢抓到流血的經驗？

And how did that work out for you?

這對你造成怎麼樣的影響呢？

Feel free to share your experiences with us in the comments down below.

請在下方留言，跟我們分享你的經驗吧。

And as always, thank you guys for watching.

照慣例，謝謝你們的收看。