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Why does your mouth go dry when you're nervous?

Image by Jaclyn Moy

You're waiting to deliver your huge make-or-break presentation.

You look around at everyone else the room. You think about your lines. And then you realise....y
our mouth has gone dry. 


In an earlier chapter, we spoke about the reptilian part of your brain - the part that regulates your body (really without much instructions you) to allow you to physically function. When blood sugar is low, it makes you hungry so that you would go eat. When your body temperature rises too much, you start sweating. 

And when you're frightened or anxious or angry (you should be familiar with the amygdala - the same part of your brain that deals with all these emotions) - when you feel threatened by something, your reptilian brain kicks your body into what is commonly termed "fight or flight".


"Fight or flight" is a survival response. Your body starts triggering hormones and entering an elevated state of preparedness. It is getting you ready to fight or run.

We're familiar with the more obvious effects. Your blood pressure rises. Your heart-rate goes up. Your breathing gets heavier. What is happening is that the faster heart-rate and increased pressure allow more blood into your limbs should you need to take action.


But your body is even more sophisticated than that. 

It temporarily shuts down all unnecessary processes. For example, healing. Your body is capable of repairing itself from all sorts of ailments or injuries. Cuts and bruises heal by themselves. White blood cells are constantly fighting off potential threats. And you're healing from any muscular tension. But all these repairs stop when you are in fight or flight. It doesn't matter if your cut heals if you don't make it past the immediate threat. 

Another example: your digestion stops. Energy is diverted away from digesting food (not very important at this moment) to your limbs and cardiovascular system, in case you need to make a run for it, or start fighting. 

So why does your mouth go dry? Because the digestion process starts in your mouth. Saliva is the first step to breaking down food to be absorbed by the body. But in fight or flight, since digestion stops, so does the production of saliva. Hence, a dry mouth.

If you think about it, your brain and body have evolved to be pretty awesome. It understands, without you ever needing to learn this, threat priority. There's no point repairing injured parts or digesting food if you don't survive the impending threat (although we shall see that our assessment of what is threatening can be pretty bad). It automatically gathers all your resources and concentrates them to help you get through whatever that is making you frightened or anxious. Like a super chief operating officer. Pretty impressive huh?

There're important implications as we understand our body's automatic responses:

  • survival is deeply wired in us, and

  • fear is our favourite tool for survival. If we are afraid,  we tend to pick the least risky, safest, most conservative option

  • The triggering of fear is automatic and subconscious. This is the case for all emotions. You don't tell yourself to be fearful or disgusted or sad - emotions simply happen to you.

  • For example, you didn't need to tell your body to stop digestion or healing, or to dilate blood vessels and increase blood pressure. All of these happen automatically, without you telling your body to do so

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