Why do some people get faint at the sight of blood, but others don't?

I was getting my morning coffee this morning at the little coffee bar in our office building and one of the coffee clerks accidentally cut her hand. Didn’t look like amajor cut, but it was bleeding a bit.

But then one of the other coffee clerks said “oh my knees are wobbling.” we alllokked sureprised, because it was just a bit of blood, but looking at her face it was clear that she was feeling faint. The one who cut herself wen into the backroom together a bandage, and the other one gradually got her colour back.

So, why do some people get faint at the sight of a little blood, while for others it’s just “hmm, you should put a band-aid on that - but can I get my coffee please?”

How about this. Over hundreds of thousands of years, animals who tear off one of their legs will survive better if something lowers their blood pressure or makes them lie down on the ground. The ones who stand up and watch the squirty blood will tend to have less progeny, on average.

I imagine that “blood/fainting” genes get passed around just as much as “sharp branch stabbing towards crotch” genes, and “chewing on pieces of rock” genes.

Hmmm. I’d expect that the same evolutionary forces would create responses in the opposite sex which make you seem more attractive if you faint at the sight of blood, etc. The “blood fainters” and “easily creeped out” have strong defenses and do better in the long run, so anyone attracted to them as mates would also do better. Similar to genetically-programmed sexual attraction caused by male’s big muscles, winning fights, able to afford expensive clothes etc. :slight_smile:

There’s a specific condition about this, it was on an episode of House MD. Maybe somebody can point to the exact terminology.

That doesn’t explain why some people do and others don’t.

There’s hemophobia (which oddly would literally be the opposite of hemophilia). More broadly there’s blood-injection-injury phobia. These can lead to vaso-vagal syncope.

It goes back a long ways - the Talmud mentions it as a factor that would disqualify someone from being a soldier. I have no idea what causes it, but it’s not due to sanitized modern living, at least.

My father is like this. He’s sensitive to all discussions of anything vaguely medical, also. Back when I was a biologist, he wouldn’t let me discuss my experiments over the dinner table, even though I worked exclusively with tissue culture, ie cells that grow in dishes.

This doesn’t answer your question, but it’s a related question itself –

When I was in high school I volunteered at an animal hospital, and one day I was in the examination room with the vet, a vet-in-training (a veterinary resident?), and a poor bull terrier that had cut its paw and needed stitches. I ended up having to assist the vet in holding the dog on the table, because the vet-in-training had almost fainted from the sight of the blood.

Which led me to wonder, does that sort of response to blood come and go? I can’t imagine that was her first exposure to a bleeding animal, so I wondered how she could have come so far in her training and just then realize the sight of blood made her sick.

My sister no longer allows her husband (the state trooper/CSI) and I to talk about his FBI splatter school (yes, there is such a course) experience at the dinner table. She cites one too many occasions where we put her off her feed. Deliberately, she swears up and down. :eek: :smiley:

I do apparently have an usually-strong stomach for a woman. When I was a reporter, I sat in on two autopsies – one fresh and one about a week old in 90-degree temperatures - saw the aftermath of people cut in half by a train, obliterated by a dump-truck, burned to a crisp after a house fire, and electrocuted. Not very pretty, yet I never turned a hair at any of them.

Back in the day, I didn’t dare show any weakness, I guess. I’d have gotten absolutely no respect from the cops and firemen I had to deal with if I had. I’m glad for my experiences but I would also never want to repeat them in this or any other lifetime.

I should mention that the same sister who got queasy over our blood-splatter tales at her dinner table also saw her daughter’s front teeth get knocked back in her throat, yet held it together to keep the daughter from panicking and her safely to the ER and stay and watch while the ER doc reached in and pulled the teeth back into place. You never know what you can tolerate until you have to.

It depends on whose blood, too. I get sick at the sight of my own blood cause it’s not supposed to be happening, but other people’s blood doesn’t bother me as much.

Warning: Wild Ass Guess Ahead

Back when I was doing a lot of traveling, I was getting a lot of shots. These shots always produced the same affect in me, I would lose all colour, begin to sweat profusely, then swoon. It always ended the same way, me lying on the bench with a microbioligist standing over me telling my husband not to worry, I’d be okay in a minute. And it always passed after a couple of minutes. I remember being told something about a Vega nerve (sp), and that if it made me feel any better I probably wouldn’t die, quite as quickly, if I was bitten by a poisonous snake? To be fair, I was in no condition to really pay attention to whatever it was that they were saying, I just wanted out of there.

So my WAG is that it’s related to the same nerve reaction.

(Personally, I was always convinced that this happened to me because I, at 100 lbs, was getting the same amount of typhoid, or whatever, as the 200 lb man beside me in the waiting room!)

I am keenly waiting for someone who knows to give us the straight dope on this!

Another WAG: we evolved a tendency for a certain small but nonzero fraction of our population to faint at the sight of blood, so that entire tribes in battle would not become extinct in one battle. There would be a small fraction that survived because they automatically “played dead”.

Similarly, color blindness seems to be an important occasional gene, because a band of observers is likelier to spot more valuable targets if some of them see differently. For this reason (I hear) bombing crews were supposed to include one color blind guy.

I’m just the opposite. My own blood doesn’t seem to bother me much, but when someone else in my family is bleeding, I just about pass out. Especially when it was one of the kids - and when they were smaller, it was usually one of the kids.

I remember one time when the ER guy was stitching up my youngest when she was about five (she took a header on a tricycle and the ground took it out on her chin - no big deal, really). He looked up at one point, saw my face and said “Sir, I want you to sit on that chair over there and put your head way down to your knees. Now stay like that. I don’t need two patients in here.”

Ur doing it wrong

I’ll see you and raise. I don’t mind the sight of my own blood at all under most normal circumstances. I don’t like it when it’s taken deliberately into ampules or donation bags, though. And it’s not the needles; shots don’t bug me in the slightest. It’s not even that I dislike it; my body reacts badly and I tend to faint.

I’d make a WAG that fainting at the sight of blood might be a way to escape an otherwise certain death. There are lots of stories where a person has survived a massacre by playing dead, often in a pile of actual dead people. These things may have happened not infrequently in early early human history, as well. So, the apparently excessive, harmful reaction to seeing blood gets passed on through generations. Then again, it may be just a meaningless quirk in the human genome and such a slight disadvantage there’s never been any evolutionary pressure to weed it out.

I’d suggest that there is probably a gene (or combination of genes) that lowers one’s blood pressure at the sight of blood (it might be your blood!).

This gene has probably saved some people’s lives in the past, and therefore some people have it now. The fact that some people don’t have this gene, means that it’s clearly not critical to surviving.

I know that when I was younger I had this brilliant idea to paint one of my rooms blood red. It looked great on the colour card!. But as I was painting I realized that I might have a bit of a problem… I had to go out and buy some non-red paint to immediately paint over it.

It’s not a consistent phobia.

My wife is a final-year medical student. She is generally fine with blood. She’s done shifts in A&E with accident victims, and while it’s never pleasant, she’s got no problem with the blood and gore. She’ll happily hold a patient’s nearly-severed arm, or assist with an open-cavity surgery etc.

But if I or our daughter cut ourselves my wife cannot cope at all. When our daughter was learning to walk last year, she tripped and banged her nose. Tiny little nosebleed, barely a trickle of blood. But my wife completely lost it - shaking hands, weak knees, barely coherent.

Likewise when I cut my finger on a broken glass in the sink - wife couldn’t bear to look at it, but I was fine and slapped on a plaster.

So in my wife’s case there’s defintely a contextual aspect to it - when it’s someone she cares about it’s much worse than someone she doesn’t know.

ETA: Similar to **Anaamika **and Balthisar’s points, only the other way around.

I had a good friend who got woozy whenever she saw blood. We were at a party once and this kid got cut in a fight – damn near lost his ear. I have a very strong stomach and rushed to administer first aid on the kid. But first I had to get her out of sight of the guy before she passed out on me.

I could never quite square that up with the fact that she was confronted with her own blood approximately once a month. Does she change tampons without looking? I’m curious to ask the ladies: how do you deal with your period if the sight of blood makes you faint?

I have a friend who is very strange in this area. She’s about as squeamish as a thoracic surgeon, but if she has so much as a single tube of blood drawn, she faints. Her father, who was also not in the least squeamish, was the same way. There’s no emotion involved; it appears to be a purely physiological reaction. Yet as far as I know, if she cuts herself and bleeds, even pretty heavily, she doesn’t faint. (As far as I know, she’s never severed a major blood vessel, so I don’t know whether or not she’d faint them.)

I suffer from this. It’s called vasovagal syncope. The sight of certain “triggers”, and it varies from person to person but often involves blood, causes blood to pool in my legs and I sometimes lose consciousness. If I sit or lay down quickly and elevate my feet I can often avoid passing out, but I sometimes get sick to my stomach instead.

It doesn’t happen very often in my case, and is probably linked to a gene (my mother and grandfather suffered from it although my dad and brother don’t) that has managed to survive through the generations.

Here’s more than you probably wanted to know about it…

Have pity on people who suffer from this… it can be quite debilitating at times.

Because some people are wimps. :smiley:

Four of my family members are or were EMTs. Conversation at the Thanksgiving dinner table inevitably got kind of gamey.