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Similarly, what makes a wet down comforter so stinky? Why do they make no smell except when liquid is added?

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I don't think pheromones play into this at all. –  jonsca May 30 '12 at 8:03
    
I would say this would have to do with the proliferation of fungi... –  Gabriel Fair May 30 '12 at 12:41
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This is kind of a physical chemistry question really as it is related to the evaporation of volatile compounds rather than biochemistry specifically. –  Ben May 30 '12 at 14:56
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Thanks for the tag change. It wouldn't let me create tags and dog, fur and feathers didn't exist. (Probably good that it didn't let me create tags...) –  Tom May 31 '12 at 8:33

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up vote 9 down vote accepted

From this source,

We answered this question on the show...

We posed this question to Dr David williams from the Veterinary School at the University of Cambridge... David - First of all, what actually makes something smell? Molecules have to leave the smelly objects and get to your nose through the air and that means that these molecules must be very small and volatile. That's to say they must be easily evaporated. The chemicals that make dogs smell are mostly what we call volatile organic acids and they are produced by bacteria from the fats that are breaking down from sweat; and that's maybe why we find these body odours unpleasant. They signal a presence of bacteria and decay and death to us.

Their [dogs] skins mostly have Staphylococcal bacteria, which don't produce much in the way of a smell at all, but they've also got some yeasts too which are really pongy. But why does the smell seem worse when the dog is wet? Here, I think we have to go into some physics. The amount of evaporation of a substance is related to the concentration of the compound on a surface it’s evaporating from and the amount of compound that's in the air, just above the surface.

So how might that change when it’s wet?

Well, if the organic acids are dissolved in water on the fur of the wet dog, as the water evaporates, the concentration of those smelly acids increases, so they'll evaporate more, so there are more molecules in the air for us to smell. Diana - A bit of evaporation can effectively amplify the amount of volatile chemicals that emanate from a dog’s skin, and Dr. Williams thinks it’s the same effect that causes that damp earth smell when it rains. It may also alter how dogs interact with each other when they're wet. So, if you have a dog, watch to see if it sniffs differently at other dogs on a dry day versus a wet one...

There's a start, sounds legitimate to me...

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Excellent! And I had read somewhere that "after rain" smell is due to rain drops pummeling the ground and dusting up molds. This makes much more sense to me. Thanks! –  Tom May 31 '12 at 8:32
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The "after rain" smell is technically called "petrichor". In summary, compounds from plants emitted during dry periods get absorbed into rocks. Rain releases these compounds and the smell derives from these compounds. The wikipedia page is a good place to read more about petrichor. –  gkadam Aug 21 '12 at 15:39
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And that's why flatulence smells more in the shower. –  ZafarS Nov 7 '12 at 18:07

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