Why Do Some People Faint At The Sight Of Blood?

Josh explains the science of why people faint at the sight of blood.

Fainting at the sight of blood, which is a condition called either neurocardiovascular syncope or vasovagal syncope, is actually related in some cases to what's classified as a blood injury phobia. Something like 3-4% of people have a blood injury phobia. But what's really interesting is that 15% of people faint at the sight of blood. Which means there's a lot of people out there who really have no issue with cutting themselves, but still faint dead away anyway when they see themselves bleeding. That's kind of weird.

When you faint from anxiety, which is what researchers think is going on when you faint from the sight of your own blood, your blood pressure suddenly spikes. But then, just as quickly, it decreases. And that decrease in blood pressure drains blood away from your brain, causing you to lose consciousness.

When you're anxious or when you feel like you're in danger, it's normal for your blood pressure to rise. It's part of the sympathetic nervous system's "fight or flight" response. What's unusual in this case, is the sudden decrease in blood pressure that causes you to lose consciousness.

At the center of all this oddness is the vagus nerve. It's a major nerve that connects your brain to various regions of your body that are involved in involuntary movement. Like your heart beating, your throat swallowing, that kind of stuff.

And at the other end, your vagus nerve is connected to a region of your brain called the nucleus of the solitary tract, or the NST. The NST is kind of like a toggle switch that goes back and forth between the sympathetic response (your fight or flight response) or the parasympathetic response, which is what calms you down after danger has passed.

What researchers think is going on is that the NST gets some sort of confused signal from the vagus nerve that causes it to decrease blood pressure as part of the parasympathetic response, without deactivating the increase in your heart rate. Which causes a lot of blood to suddenly be pumped away from your brain, hence making you pass out.

Another explanation is that your NST simply toggles too quickly between the sympathetic and parasympathetic responses. Like it's working its joystick, like, "What's going on?" And then you're out on the floor.

Then there's another parallel hypothesis, that because your NST is also in charge of mediating your disgust response, that there's some sort of mixture of fright and disgust that causes you to faint, because, again, the NST is confused.

However you slice it, it seems that you can lay the fainting at the sight of blood thing at the feet of the NST.

Evolutionarily speaking, passing out at the sight of your own blood doesn't make much sense. And researchers have bent over backwards to try to explain it. What they've come up with is that, possibly, when you faint at the sight of your own blood, say, after being mauled by a bear, the bear will take you as being dead and will lose interest. Pretty lame.

Another more reasonable (in my humble opinion) explanation is that this sudden decrease in blood pressure prevents us from bleeding out of some sort of wound, and that the fainting is just an unfortunate byproduct of the whole thing.

Either way, at any rate, whatever the case, once you're on the floor, which is usually what happens when you faint, the blood flow to your brain can be restored fairly quickly, because it's a lot easier for your heart to pump blood horizontally than upwards against gravity.

SOURCES:

[TheMuteGamerTV]

I don't faint. I just feel very weak

[clowncores]

I don't faint straight away I just look at it and feel really weird and I feel scared and disgusted then I faint

[ohsonnif]

Who else doesn’t feel good when they hear the word “Blood”

[_domgutz]

who else here fainted just before watching this 😆

[saketsoni]

Anyone here watching who is from those 15% people? I'm one of them!!

[mattwood]

I'm in the 15%, I'm not scared of it but for some reason I just faint anyway 😕

[sparkle]

I sometimes faint at the sight of blood, but not menstrual blood for some reason. Also, once I fainted because I was thinking about fainting 😂😂😂
It was in front of my entire class!

[xKitra]

I've never actually fainted, just to the point where my eyes are open, my vision is gone, my hearing goes away, and I have to lay down asap which helps restore the blood flow to my brain. I've gotten better over the years at trying to control it, identifying the triggers, distracting myself or leaving the situation if I can, but it still hasn't gone away. It's very annoying having to explain to a room full of people why I'm randomly laying down. Like at my new job's first aid training class. Embarrassing but its a part of me and something I need to live with.

[imgriizzly]

Had some blood tests done today. I’m feeling weak during the hole process as well but I’ve found a way to fight it off. I lay down with my headphones, put some music and read something on my phone that distracts me from the whole process. It really works for me.

[MrLongman]

For me, when someone talks about a surgery or serious injury I feel dizzy and anxious. I once lost consciousness when my friend's father was explaining me why doctors had to amputate his toe. I think that not only me that has this problem, right?

[Rexpi]

ahhh man, i wasn't fainting at the sight of the blood when i was a kid. Now when i was 11, just a little tiny blood came out of my arm I just fainted right after i saw it. now i'm 14, i still have it. And also when someone talk about blood or some lesson in school, my blood pressure goes down.

[meghanlivingstone]

I find this so interesting! I have fainted a number of times in my life due to cutting my finger and I've always wondered why.

[unknownavatar]

When I see blood I feel really weak and feel to lay down. My vision starts to turn white and then I see total dark. I hear a little noise at that point (not all the time). I feel dizzy and also kinda hungry. If I lay down for a few mins it starts going back to normal. I don't know the name of this disease but I'm kinda worried about it. It only happens when I see my own blood. But when I see others blood or cut it also happens but not so much as my own, only weak feeling or sometimes nothing. But I have to get out of there soon otherwise I don't feel good. But if I see it in the movies it never happens. Yeah if it's really brutal and gore I feel disgusted but it never happened like it happens when it's my own blood or cut.

[colesbrown]

My ears start ringing and I get sweaty. I also turn very pale.

[anarkitty]

i think its the panic combined with your body saying "GET BLOOD AWAY FROM THERE!", lowering your blood pressure.

[ShubhamKhandelwall]

even hearing about blood don't make me feel good, , seeing is very different thing. Why????

[wilesy]

I'm very squeamish, in fact so much that I almost fainted while looking at the thumbnail

[ahamed]

Who are all fainted while taking blood test ? I'm one of them and the incident happened today

[prabhakarkumarsharma]

I always faint whenever I have to give a blood test, there's something about those syringes piercing your nerves and the blood getting sucked out of your hands, the visuals of blood filling in the syringe.
I don't know what it is or why I'm so afraid or how I became like this, but it is what it is.
Today I fainted again and searched for what I can do to prevent it, and here I am.

[TheGuyNobodyReallyLikes]

Not only do I faint at the sight of my own blood or other peoples blood, I also faint after seeing my own injury or other peoples injuries that may or may not have blood in them. And I also have a fear of sharp objects such as thorns, needles or knives. If I do get poked by a needle, then if I don't faint, then either I'll vomit or have an upset stomach and would like to go to the washroom. Or I'll have a combination of those and my body will remain paralyzed for a few minutes. This also runs in my family as some members are affected by the sight or blood or injuries, while others aren't at all.