爲什麼鼻子每次只堵一邊?

Though you may not pay attention to it unless you're sick, you're always breathing more heavily from one nostril than the other.

除非生病了，否則你可能並不會注意到，你的一個鼻孔總是比另外一個呼吸更費力。

During the day, the sides switch and the other nostril goes into 'work mode', but why?

一天之中，兩邊的鼻孔可能會交換，另一側的鼻孔進入“工作模式”。但這是爲什麼呢？

This process is automated by the aptly named autonomic nervous system, which is the same system that controls many things your body does all by itself such as digestion and heart rate.

這一過程由自主神經系統自動控制，這個系統也控制着你身體自動運轉的許多方面，比如消化和心率。

For your nose, this system controls your 'nasal cycle', so that each nostril operates effectively.

對你的鼻子而言，這一系統控制着你的“鼻子循環”，便於每個鼻孔有效工作。

The nasal cycle happens, according to the US National Library of Medicine, several times during the day, and is only brought to your attention if your nose is clogged up more than usual.

據《美國國家醫學圖書館》透露，鼻子循環一天會出現好幾次。只有當你的鼻子比平時更堵的時候，你纔會注意到這一點。

In order to open one side of your nose and close the other, your body inflates tissue with blood in your nose.

爲了打開一邊的鼻孔、關閉另一邊，你的身體會讓鼻子裏的組織充血膨脹。

"Increased blood flow causes congestion in one nostril for about 3 to 6 hours before switching to the other side. There is also increased congestion when one is lying down, which can be especially noticeable when the head is turned to one side," Jennifer Shu reports for CNN.

據美國有線新聞網的詹妮弗-舒報道：“血流增加會導致一邊的鼻孔堵塞3-6個小時，之後纔會轉移到另一邊。人們躺下來的時候，鼻孔堵塞程度也會增加。人們將頭轉向一邊的時候，這一點會格外明顯。”

It's believed that this cycle helps round out your sense of smell. As Matt Soniak reports for MentalFloss, some smells are better picked up by fast moving air through your nose, while others take more time and are detected better with slow-moving air.

據稱，這種循環有助於豐富人們的嗅覺。據MentalFloss網站的馬特-索尼亞克報道說，某些氣味能更好地被鼻孔中快速氣流捕捉到，而其它氣味需要更多時間被慢速氣流捕捉到。

If one side of your nose is wide open and the other is slightly closed, you get all of the smells.

如果一個鼻孔張得很大，而另外一個鼻孔略微閉合，那麼你就能夠聞到所有的氣味了。

The process also gives each side of your nose a break, since a constant stream of heavily flowing air can dry it out and kill off the small hairs that protect you from foreign contaminants.

這一過程也能讓你的兩個鼻孔稍微休息一下，因爲如果不斷有大量空氣流過鼻孔，會導致鼻孔乾燥並損害鼻毛，鼻毛能夠保護你不受外來污染物傷害。

When you get sick, the whole process can become unbearable, because the one nostril that is effectively 'turned off' feels way, way more clogged than the other, Soniak says.

索尼亞克說，當你生病的時候，這一過程會變得令人難以忍受，畢竟其中一個有效“關閉”的鼻孔會讓你感覺比另一側更堵。

Basically, the clogged-up feeling is just amplified by the cold.

基本上，感冒會使鼻子堵塞的感覺放大。

So the next time you feel like you're only breathing from one side of your nose, remember that it's a natural, automatic system working to keep you smelling properly, and to make sure your nose doesn't get dried out by a constant onslaught of dirty air.

下次，你感覺自己只能用一側鼻孔呼吸的時候，請記住這是一件很正常的事。你的自主系統正在幫助你恰當地聞到氣味，並確保你的鼻子不會因爲不斷呼吸骯髒的空氣而變得乾燥。