Science Questions

Why do people instinctively suck on a bleeding wound?

Mon, 28th Sep 2015

Listen Now    Download as mp3 from the show Why don't spiders get stuck on their webs?

Question

Dennis W. Cooper asked:

Hi Chris,   Love your show. 

 

Here is my question:   Why do people instinctively suck on a bleeding wound, e.g., a small cut on a finger?  Since the mouth contains many germs, it would seem that a person would not want to do this?

 

Thanks,

 

Dennis Cooper Santa Barbara, California, USA

Answer

We put Dennis' question to Dr Chris Smith

mouthChris - It does sound counterintuitive, doesn’t it? Probably, there are two aspects to this. Number one is that whenever you injure any part of yourself, the reaction or the reflex response is usually to rub it better. When you rub something better, what you're doing is stimulating the nerve cells that convey low threshold stroking sensations to your brain. Those nerve cells are wired up in your spinal cord to inhibit or switch off the nerve cells that convey pain. So, by sucking on an injured body part, you're stimulating those big low threshold nerves with that stroking sensation and thereby, blocking the pain. Number two is that actually, although your mouth is full of germs, they are a fairly unique repertoire of germs that include streptococci that we call Viridans streptococci, some staphylococci, they're generally low pathogenicity bugs. They probably are not going to be bad for you in a big way. As a result, your immune system is pretty good at dealing with them and if you pushed a few of them into your wound, probably not going to do much harm. Also, when you clean the wound with your tongue or by sucking, you're going to dislodge foreign matter. You're probably going to dislodge some nastier bugs that might be in there and they’ll get swallowed and then destroyed by your stomach acid. Here’s the real sort of clincher for this argument which is that every time you clean your teeth then if you do tests on people, you can detect showers of microorganisms and their DNA going around your bloodstream because when you clean your teeth, you make little lacerations in your gums. Also, when you eat food, same story, when you floss your teeth, little holes open up in your gums, and the bugs in your mouth get into your bloodstream. In the vast majority of cases, they're harmless to you because your immune system deals with them straightaway, your spleen filters them out, never a problem. In a small minority of people, usually people who’ve got pre-existing problems with the valves in their hearts then these microorganisms can sometimes settle on the valves of your heart and they cause a condition called endocarditis. But for the vast majority of people, it is not a problem. So, there's the evidence that you're probably not carrying anything in your mouth that you're going to add to your wound and make yourself sick with it.

Multimedia

Subscribe Free

Related Content

Comments

Make a comment

Dennis W. Cooper asked the Naked Scientists: Hi Chris,   Love your show.  Why do people instinctively suck on a bleeding wound, e.g., a small cut on a finger?  Since the mouth contains many germs, it would seem that a person would not want to do this? Thanks, Dennis Cooper Santa Barbara, California, USA What do you think? Dennis W. Cooper , Wed, 20th Apr 2011

I've always wondered that too. And it isnt just a stupid human trick, since animals seem to lick their wounds as well, at least dogs and cats anyway. All I can figure is that perhaps your own mouth bacteria are less likely to be pathogenic than soil organisms. I suupose cleaning a wound with saliva might be better than nothing. There are small amounts of secreted antibodies in spit, but I don't know if its enough to have any effect. I also wonder if there's anything in saliva that makes blood clot faster. People also seem to do this, though, in response to other injuries, even when the skin isnt broken, like when you hit your finger with a hammer. Maybe it decreases the pain sensation. cheryl j, Tue, 22nd Nov 2011

evolution=2 early hunters,hungry, hunted a boar & both failed & ended up bleeding. 1 sucked his blood & the other didnt CZARCAR, Tue, 22nd Nov 2011




http://bloodjournal.hematologylibrary.org/content/early/2011/01/19/blood-2010-06-290460 RD, Tue, 22nd Nov 2011

See the whole discussion | Make a comment

Not working please enable javascript
EPSRC
Powered by UKfast
STFC
Genetics Society
ipDTL