It’s time to give that big presentation.

You look around the room and see the faces of  people you need to impress staring back at you. Then you feel your own face go  pale, and your heart starts to race.

Your jaw is clenched, and for some reason,  your shoulders are tightening and raising. This is a critical moment in your career,  and your body is completely betraying you! But there's a good evolutionary reason  that you react this way under stress.

The same fight or flight impulses that are ruining   that powerpoint presentation have also  served humanity pretty well in the past. Our bodies have a hard time telling  the difference between the stress of   being chased by a bear and being  chased by a project deadline. So let's look at five weird  fight or flight responses   your body has when you're perfectly safe. [♪ INTRO] As smooth as you might think you are, it’s clear to anyone looking at you that  you’ve entered fight or flight mode.

Often, the blood will drain away from parts  of your face, and you look really pale. And I said parts of your face, because  it doesn’t drain from the whole thing. It just moves to a place  where it can be more useful.

It gets shuttled to the area around your eyes. And that helps you make quick eye movements, which you might need when, say,  planning and executing an escape. That’s really helpful when  you’re running from a grizzly.

But less so when you’re trying to keep  your cool in a stressful conversation. Because blood flowing away from most of your face  just shows the other person how stressed you are. Now I have to give a quick disclaimer here  that I’m talking about temporary, acute stress.

Chronic stress is a different thing,  and this video is not about that. A lot of the ways your body goes into fight  or flight mode are okay every now and again, and might even provide a momentary benefit to you. But if your body is constantly doing  this stuff, it can become harmful.

OK, back to going pale. To show how this happens, one  small experiment involved 32   people who were put in a fake crime interrogation. Some of the participants were told  to steal a gold necklace from the   lab while the others didn’t get that instruction.

Then they were interrogated  in front of a thermal camera. The thermal camera was supposed to  capture the fight or flight effect   of blood redistributing throughout their faces. Using an AI tool to analyze the thermal data,   the researchers could accurately guess who was  innocent and who was guilty 87% of the time!

Which means that professionals  can use the movement of your   blood away from parts of your face  as a reliable indicator of stress. But since those participants were following  instructions and didn’t necessarily feel much   heat for their crime, you might not be convinced  that this technique really reveals all that much. For the skeptics, another experiment  published in 2006 might be more compelling.

These participants were selected because they  felt really strongly about something political. They might have been pro-choice for example. And they were told that there  was a check in an envelope just   down the hall made out to an opposing  group, like a pro-life organization.

Then they could choose whether or not to steal it. Another important part of this experiment was  that they needed to convince the interrogator   of their innocence or else the organization  they didn’t like would get the money. This experiment might be  considered more consequential.

The crime was more genuine, and  there was motivation to do it. And researchers ended up being able to  identify the criminals and the innocent   participants with almost exactly the  same accuracy rate as in the other study. So both of the studies were able to use facial   blood flow changes to reliably  tell when a person is stressed.

But that’s just one physical sign of stress. You don’t need a thermal camera  to see when someone tenses up. You know when you’re so stressed that you have to  actively tell your shoulders to go down and relax?

Or you finish that project and  suddenly realize your jaw hurts   because you’ve been clenching it the whole time. Or your hand cramps up because you’ve  been gripping the pen so tight? That’s your muscles’ stress response.

If you were in a real fight or flight  situation, you’d be tensing to protect yourself. Like if you had to jump off a cliff into  the water, you’d brace yourself for impact. But when you’re writing a  paper, sure it’s stressful, but you don’t need to brace yourself that way.

It won’t get the job done any faster. It’s just a stress response  we can’t seem to shake. One study tested this effect using  electromyography, or EMG measurements.

An EMG assesses the electrical  responses from your muscles. And in this case, they were testing  the participants’ muscle responses   to the anticipation of an electric shock. That’s not quite the same kind  of stress as a presentation, but this study gives us an idea of how  your muscles respond to stress in general.

And don’t worry, these shocks  weren’t enough to do any damage. The researchers were interested in  the response to not just physical,   but also psychological stress anyway. To get both of these factors  into their study design,   they told participants they were going to  stress test them with an electrical shock… but the participants wouldn’t  know when the shock was coming.

That way, they could get pre-stress, immediately  after stress, and post-stress muscle reactions. They found that just waiting for the shock  to happen led to increased muscle tension, with participants’ pre-stimulus muscle  tension higher than at baseline. Then when the shock finally  came there was an immediate   spike in tension, followed by a decrease.

So basically, it’s not just the pain that causes  muscle tension, but also the anticipation of it. And even though you might tighten up from  both physical and psychological stress, this study was just describing  a physical tensing response. The next item on our list shows how intense  the emotional response from stress can be.

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And if you can join them responsibly, we would  love to have you at patreon.com/SciShow. If you feel emotionally sensitive  during stressful situations, that’s clearly not helping you  accomplish whatever is stressing you out. Crying in an interview won’t get you the job and   yelling at your coworker won’t help the  team work together to finish a project.

But sometimes, our emotions get the best of us. This happens because the emotional  regulation center of your brain, a region called the amygdala, is one of the main  areas controlling how you respond to stress. When you suddenly find yourself in that  kind of situation, your amygdala responds by sending fast-acting chemical signals to other   parts of your body to boost  its overall excitability.

This makes you more vigilant  and able to respond to threats. The side effect of activating your  emotion center is, well, emotion. One study published in 2022 investigated  how the amygdala communicates with other   parts of the brain during stressful situations.

Specifically, a math test. Many of us dread the idea  of any kind of math test. But this one was made even more stressful  by time limits to answer each question, pressure to get them right or  else the data wouldn’t be used, and disappointed feedback from the experimenters  when a participant missed a question.

That is my own personal hell... During that stress nightmare, the participants  had functional magnetic resonance imaging,   or fMRI, readings to see what  was going on in their amygdalas. The main conclusion was that the parts  of the brain keeping your amygdala in   check aren’t communicating with it as  much when a stressful event happens, and that might be why you  respond to it so emotionally.

This builds on an earlier  study that found that the   amygdala is more responsive yet less  selective in stressful situations. Since you’re in fight or flight mode, the default  is that everything is important to respond to. That adaptation to increase vigilance with the  side effect of lowered emotional inhibitions might help you notice a jaguar emerging from the  shadows, but it could ruin your office banter.

And emotions aren’t the only thing  stress can make you lose control over. Sometimes, it makes it hard to  control things as basic as breathing. When you’re about to knock on your boss’s door, you might feel your heart start to race  and begin breathing faster than you’d like.

While that’s not going to improve  your conversation with your boss, it can be helpful in other  fight or flight situations. It’s all in service of getting more oxygen  to your cells so they can use energy. You don’t need that much  energy to chat with your boss,   but you might if you’re running from a predator.

It’s another example of your body doing  a thing that was once very useful. But enough about physiological  changes that kind of make sense. Let’s get to the weirdest  stress response of them all.

Whenever you’re in a tense situation, you may  find yourself indulging in more snacks than usual. After completing a big project,   you might look around to find a  room covered in crumbs and wrappers. That can’t be a positive stress response.

In fact, it confused researchers  who study this stuff for years. Because “Fight or Flight” is supposed  to be the opposite of “Rest and Digest”. In these situations, your appetite should be   suppressed so your body can  focus on the task at hand.

And one of the chemicals that suppresses appetite  is adrenaline, which is released during stress. But the thing is … some people do the opposite and  up their junk food intake when they’re stressed. It’s me, I’m people.

Since it’s an excellent way to not gain an  advantage in a fight or flight situation, scientists called this the  “stress-eating paradox.” And in 2022, a study helped solve this mystery. It concluded that stress eating is  related to how your heart rate changes. It turns out that not everyone has the  same heart rate response to stress.

Generally, your heart rate  increases when you’re tense. But for some people, it  increases more than for others. And if your heart rate increases at  the low response end of the spectrum,   then you’re more prone to stress eat.

Especially the starchy stuff. Let’s be real, how many times  have you stress-eaten tilapia? No, you go for the salt and vinegar chips.

It appears that appetite suppression might   not kick in unless your heart  rate response is big enough. Until then, you have the  opposite reaction and stress eat. So everyone responds to  stress a little differently.

But regardless of what your body does, some  of it probably seems pretty unhelpful today. Your fight or flight responses can get triggered   by psychological stressors that  aren’t at all life threatening. But remember: they’ve served us well  in the past, and still do on occasion.

And now that you know where these weird responses  come from, you don’t have to stress about them. [♪ OUTRO]