Why does blood make us faint?


Do you ever get dizzy and sick from the sight of blood? Every movie, TV show, or picture that contains blood, real or fake, is enough to make me sick, or in some instances collapse to the floor. I always assumed it was normal for people to faint at the sight of blood since it is normal for me, but most people do not have such a problem with it. So, what causes some people to faint when they see the red liquid, while others don’t even flinch?

First of all, it is important to see what causes fainting in the first place. This article explains what happens in the brain that triggers fainting, aka vasovagal syncope. The vagus nerve in our brains synapses onto something called the nucleus of the solitary tract, abbreviated as the NTS. Stimulating the NTS is what causes the bodily functions that lead to fainting: a drop in blood pressure, drop in heart rate, etc. The nerve stimulations are triggered by stressful events. This explains why things such as hunger, dehydration, and intense heat are such common reasons that people lose consciousness. So, where does the sight of blood play into all this? For some, that scene can register as a stressful event. Stress and intense emotion are factors that trigger the vagus nerve to synapse, and so if someone is very sensitive to gruesome scenes, the NTS will be stimulated just the same. So, it is really up to how each individual interprets the scene in front of them. Some people may just feel uneasy and turn their heads, but others can register this on a deeper level, which leads to the common phenomenon of people fainting at the sight of blood.

I do not think an experiment can or needs to be done to test this, since it really depends on the individual and how they process what they see. If we see a gruesome image in class, each student is bound to react to it differently. This cannot be due to reverse causation either, because we know that fainting is final result, not the cause. So the takeaway from this is, if you have a tendency to get woozy from seeing blood, then you should avoid some horror movies or some PowerPoint slides in class. If you do not feel any discomfort when seeing certain images, then go right ahead and look; your nervous system will be just fine.

2 thoughts on “Why does blood make us faint?

  1. Alyssa Marie Gregory

    Wow! This is new to me I thought passing out at the sight of blood was always just in Hollywood films. In your post you made lots on connections to what we have learned in class which was good! I can agree where you say that we can rule out reverse cassation. But I must pose a counter argument when you say we couldn’t really test this hypothesis. While we(us blogging students) wouldn’t have the resources to do an experiment I believe that someone with the right resources, time, and knowledge could actually test this. If we got a large group of people just like you (who faint at the sight of blood), monitor their brain and nerve activity we might actually come to a sound conclusion about what exactly it is that triggers them to faint. While myself along with the other girl who commented both say we don’t know someone who faints off the site of blood we still have to dig deeper as scientist and realize there are other opinions and people out there. with that being said here is a link with other people who say they faint at the sight of blood as well .

    Ps. if we were ever able to get an experiment these people would probably be a subject

  2. Tiffany Elizabeth Breon

    I’m not going to lie, I giggled to myself when I read “…or some PowerPoints in class…” but this topic did strike me as interesting. I’ve personally never known anyone who faints at the sight of a particular thing but I always see it in Hollywood films (and it’s usually a woman who faints at the sight of something traumatic). It’s interesting that certain things can just set off your biology like that. I have a similar problem, except I do not know what sets it off. I have these random episodes of vertigo that cause me to sometimes have to grab something while I’m walking to prevent from falling. I know vertigo is usually caused by sudden head movements or quick motion but it doesn’t seem to happen at those times for me – it literally will happen in the middle of class sometimes. It would be interesting to know what can cause that kind of vertigo since I’ve never heard of any vertigo that happens randomly without any other symptoms. Here’s an article that talks more in-depth about lightheadedness and vertigo: http://dizzy.com/dizzines_and_equilibrium.htm

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