如果你不小心在安静的会场发出了恼人的声响，如果你说了不该说的话后悔莫及，如果你看见了暗恋以久的人对你微微一笑……每每这时候我们都会脸红。为什么人会脸红？下面的文章会给您一些启示。

You can't believe the words that have just come out of your mouth. You certainly didn't mean to insult the woman in line ahead of you, but it's too late now. She's staring at you angrily. You feel a sudden jolt¹ as your heart rate increases. You have a coppery taste in your mouth, and your cheeks begin to feel warm. You, my friend, are embarrassed, and you're blushing because of it.

Blushing and embarrassment² go hand in hand. Feeling flushed is such a natural response to sudden self-consciousness that if it weren't part of an emotionally crippling experience, it could almost be overlooked. But blushing is unique, which is why scientists want to know more about blushing. While the psychology³ of blushing remains⁴ elusive⁵, we do understand the physical process involved. Here's how it works.

Blushing from embarrassment is governed by the same system that activates⁶ your fight-or-flight response: the sympathetic nervous system. This system is involuntary, meaning you don't actually have to think to carry out the processes. In contrast, moving your arm is a voluntary action; you have to think about it, no matter how fleeting⁷ the thought is. This is good, because if moving your arm was involuntary, people would end up buying a lot of stuff they don't want at auctions⁸.

When you're embarrassed, your body releases adrenaline (肾上腺素). This hormone⁹ acts as a natural stimulant¹⁰ and has an array of effects on your body that are all part of the fight-or-flight response. Adrenaline speeds up your breathing and heart rate to prepare you to run from danger. It causes your pupils to grow bigger to allow you to take in as much visual information as possible. It slows down your digestive process so that the energy can be redirected to your muscles. All of these effects account for the jolt you feel when you find yourself embarrassed.

Adrenaline also causes your blood vessels¹¹ to dilate¹² (扩大) (called vasodilation 血管舒张), in order to improve blood flow and oxygen delivery. This is the case with blushing. The veins¹³ in your face respond to a signal from the chemical transmitter adenylyl cyclase (腺嘌呤环化酶), which tells the veins to allow the adrenaline to do its magic. As a result, the veins in your face dilate, allowing more blood to flow through them than usual, creating the reddened appearance that tells others you're embarrassed. In other words, adrenaline causes more local blood flow in your cheeks.

This sounds reasonable enough, but it's interesting to note that this is an unusual response from your veins. Other types of blood vessels are responsive to adrenaline, but veins generally aren't. In other regions of your body, veins don't do much when adrenaline is released; the hormone has little or no effect on them.

Blushing from embarrassment is a unique phenomenon. There are other means by which our cheeks become flushed: Drinking alcohol or becoming sexually aroused can cause us to blush, but only being embarrassed causes the type of blushing that is triggered by adrenaline.

Some people opt¹⁴ to undergo surgery to limit their blushing response. Erythrophobia (害怕红色) is the fear of blushing and it can be enough that it could lead to a person choosing to have the tiny nerves at his or her spine¹⁵, which control blushing, snipped¹⁶. This surgery -- called endothoracic sympathectomy (交感神经阻断术) -- has been shown to limit blushing.