Science Questions

Why do the farts of others smell worse?

Mon, 14th Apr 2014

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Peter Steadman asked:

Why does someone's air biscuit, or the technical term for flatulence, why does that smell bad from someone else when it's not so bad when you smell your own?


Hannah - Well, I would say that my farts really are quite stinky even to myself The Human Noseand I asked my boyfriend about this and he agreed. But he said that his own farts, he found curiously pleasant - was his expression.

Chris - Is everyone universally in agreement here in the studio?

Hannah - Not about my farts, about your own.

Helen - I think itís particularly bad if itís someone elseís because itís more the thought really that itís not come out of yourself, your own body. And maybe, is it a similar thing to other sorts of bodily fluids like Ė I don't know Ė mothers get very used to their childrenís puke and poo, and all sorts of things because they kind of have to. But if it was another childís puke and poo, Iíd presume they wouldn't be quite so pleased of getting close to it.

Hannah - There have been scientific studies on farts and also, babyís poo. In a blind study, mothers find their own childrenís poo more pleasant smelling than other childrenís poo and the same can be said of peopleís farts. So, just imagining the smell of your own farts, people rate it as okay, but if you're asked to imagine the smell of anyone elseís fart then yeah, they think itís disgusting and itís possibly...

Chris - I was going to say, one theory I heard of this is that one person pointed out to me that one possibility is that the gases that you're going to release don't just come out of you, out of your rear end. Effectively, those volatile chemicals go into your bloodstream a bit and that means they get carried up to the receptors in your nose via your bloodstream and they desensitise the receptors in your nose a little bit. You effectively get used to the smells you're going to make and this means that because you've been smelling it already, it doesnít smell quite as offensive to you because itís less new to you compared with someone else whoís having to put up with it for the first time. Ramsey...

Ramsey - Similarly Chris, I believe that our sense of smell is relative. So, we get used to smells in other words. So, when you come home from holiday and you open your door to your house and you sort of think, ďOh, it smells a bit musty. I'm going to go and open some windows.Ē It might not actually be a musty house at all. That is the smell of your home. You just normally get used to it and I think we all probably know people who we think smell a lot like their dogs, or generally, smell a bit funny in general and you kind of think, how does this person not notice they're a bit smelly. Well, we all get used to our own smells and itís because itís a relative sense that we have.


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I was looking back over my life, treating it like an ethnographic study. Then I remembered two smell related experiences from the same source, that maybe shared with other peoples experiences on the matter.

They where:
Ė I can remember smelling a eggy odour in class whilst at school (long, long time ago).
It was really strong and overwhelming, it made me feel 'sick'. I found it repulsive.

-I latter found out that it was a stink-bomb, and a friend let one off again. This time armed with the knowledge of its source. I found the smell did not effect me in the same way. I was laughing and not covering my air-ways feeling sick.

These two experiences, though personal, demonstrate to me that knowledge is important to how a person reacts to olfactory perception in this case, but, possibly any sense stimuli.

Has any one else shared this experience?

I'm guessing that it is probably due to not being able to catch nasties from your self. But, its odd we have developed multiple, polar like, reactions to a singular stimuli.

repulsion is in no doubt about survival, the things that repulse us are normally hazardous in a biological way. i.e they carry dangerous germs. So people with out this reaction would of died. Thus, the preset repulsion reaction made it through natural selection.

Its amazing how powerful the influence is of our background knowledge on a emotional response to a perceived object.
fore example, Some ignorant kids are happy to eat worms in the garden. But, with a little bit of knowledge just the thought of eating worms would make some people feel nauseous. or,  that's my bodily waste, it's got my germs, therefore relatively safe to me so no need for repulsion.

I'm unsure how much of this would be naturalistic and how much is learned.

-At least this means that the trip to dump city to deposit a load does not end up being a traumatic, daily for some, repulsive experience. Peter Steadman, Fri, 11th Apr 2014

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