or a heart-wrenching break-up following your first love,

或是與初戀分開後的傷心欲絕，

crying may seem like a strange physical response to your emotional turmoil.

每當你情緒波動時，似乎都會出現流淚這種奇怪的生理反應。

Why do we start the waterworks when we feel really sad?

為什麼我們很傷心的時候就會開始哭？

Is there a biological advantage or purpose other than washing your face or streaking your mascara?

除了弄濕你的臉跟融化睫毛膏之外，流淚還有其他生理上的原因嗎？

Well crying does not only happen when you are emotional, there are actually three types of tears.

其實人不只有在傷心的時候會哭，實際上人的淚水有三種類型。

Basal tears are perpetually lubricating your eyes keeping them from drying out,

第一種，自然分泌的淚水。用來保持你的眼睛濕潤而不會乾燥，

while reflex tears act in response to an irritant like onions or dust.

第二種，反射性的淚水。通常是在眼睛受到刺激性物質，如洋蔥或灰塵的刺激時而分泌。

They begin a chain reaction releasing hormones from the brain which then

當眼睛受到刺激時，大腦會釋出荷爾蒙，產生一連串的反應，

trigger a tear response from the glands in the eyelids.

促使眼皮內的腺體分泌淚水。

And these tears help to get rid of the irritant.

讓淚水帶走刺激物質，減緩眼睛受到的刺激。

But tears of sadness? Strangely this leaky face phenomenon is exclusive to humans with a couple different theories as to why.

至於第三種，悲傷的淚水，則有一個有趣的事實，那就是哭泣的生理反應只發生在人類身上，至於原因為何，坊間各有幾個不同的理論。

And one is strikingly similar to the reason we blush, which we described in a previous video here.

其中一個原因與臉紅的原因相似，我們在之前的影片中有探討過。

In many cases

在許多情況下，

emotional tears are able to act as a signal to others of our genuine sadness or distress.

受情緒因素影響而產生的淚水可以被當作是一個表達我們真實悲傷或痛苦情緒的訊號，讓其他人更容易捕捉到我們發出的訊息。

That is not always easy to fake.

這個訊號通常很難偽造的。

Your tears blur your vision, essentially handicapping any aggressive or defensive actions

因為當你哭泣時，眼淚會造成你視線模糊，你變得無法從事任何攻擊或防禦行為，

sending those nearby a signal of need appeasement or attachment.

如此一來，你等於向周圍的人釋放出需要關注與愛的訊號。

From an evolutionary perspective, this increases communication with those close to you

從演化的角度來看，這會增加你與身旁的人的溝通，

and ultimately your chance of survival.

進而增加你生存的機會。

Some experiments have even taken photos of people crying

有些研究人員將人們哭泣的模樣拍攝成照片，

and made copies with the tears digitally removed.

再用電腦修掉他們的眼淚。

Not surprisingly, people rated the pictures with tears to be more sad,

不意外的，在人們的眼裡，流淚的模樣看起來比沒有流淚的模樣更傷心。

while the ones without were often confused with puzzlement, awe or other expressions.

而沒有流淚的模樣經常被誤解為其他的情緒，如苦思或畏怯等等。

But what about tears of joy? Well perhaps they are not so different,

那喜極而泣的眼淚呢？這兩者間或許沒有很大的差異，

afterall tears of happiness may still be used as social signals for how we feel,

畢竟喜極而泣也可以被當作是一個傳遞情感的社交訊號，

and are thought to strengthen bonds between people.

​​因此也被認為可以加強人與人之間的連結。

Also both emotions see activity in similar regions of the brain, such as the hypothalamus and basal ganglia

而且兩者在大腦的反應區域也是類似，如下丘腦與基底核，

which just happen to be connected to your tear glands.

這些構造正好都連結淚腺。

Another theory suggests that crying is one of your body's mechanisms to literally shed your stress.

另一種理論認為流淚是身體釋放壓力的一種機制。

Interestingly reflex tears and emotional tears have very different compositions.

有趣的是，反射性與情緒性的淚水在組成上有很大的不同。

Emotional tears have much higher levels of proteins,

情緒性的淚水含有相當高的蛋白質，

in particular some called adrenocorticotropic hormones which are linked to high stress levels.

特別是跟情緒壓力有關的蛋白質——促腎上腺皮質素。

And some say crying helps to release these stress chemicals from the body,

有些人說，流淚可以幫助排除人體的壓力物質，

but the research here is limited and not yet conclusive.

但是，目前相關的研究不多，所以不能當作確實的論據使用。

So go on, have a good cry,

無論如何，你可以好好大哭一場。

let the world know how you feel and potentially let out that stress.

讓世界知道你的感受，並抒發你的壓力。

Got a burning question you want answered?

還有想要知道的問題嗎？

Ask it in the comments, or on Facebook and Twitter. And subscribe for more weekly science videos.

在影片下方留言或是在 Facebook 和 Twitter 上留言。記得訂閱我們的頻道，以收看每週更新的影片。