Science Questions

Why do wet dogs smell?

Sat, 3rd Sep 2011

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Jarry D asked:

Could you please tell me why do wet dogs smell?


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 itís evaporating from and the amount of compound that's in the air, just above the surface.

So how might that change when itís 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 dogís skin, and Dr. Williams thinks itís 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...


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I don't understand the question. Don't their noses work just as well when they are dry? Geezer, Mon, 22nd Aug 2011

This is a variant of the old music hall classic...

"I say, I say. My dog's got no nose"
"Oh, How does it smell?"

Boom, boom. graham.d, Mon, 22nd Aug 2011

Well, you can't blame me for trying  Geezer, Mon, 22nd Aug 2011

Does moisture increase the emission of odors.  You can definitely smell more of the countryside after it has rained and I suspect that this might be due to bacteria that are able to use this moisture to dramatically increase their numbers.  People stink of BO after they have been sweating and again this is due to bacteria.  That's my guess anyway.

It could also be that when an animal is wet the cause of the odour is essentially diluted into the water and as it dries through evaporation the bacteria responsible for the whiff are distributed into the air making them more detectable for our little noses. 

Aaron_Thomas, Mon, 22nd Aug 2011

I think their hair are too thick so when it gets wet it smell...  urmin, Tue, 30th Aug 2011

Because dogs smell and when wet their body heat causes evaporation of water and odors. This is why I only have cats. Dowsett, Wed, 31st Aug 2011

People smell a bit when wet though too don't they? Wet hair definitely has a characteristic scent. chris, Thu, 1st Sep 2011

I was not far off the mark was I?  Aaron_Thomas, Fri, 30th Sep 2011

It amazes me that most people don't realize that particles must actually physically move through the air to your nose. So when you produce flatulence, particles from your rear end actually touch the noses of people surrounding you in order for them to smell it :) That being said, I love that fact that you noticed the use of increased surface area. In science it seems like the volume to mass ratio, or the surface area to volume ratio quite often is the reason one thing will go one way or the other. I love it! The Penguin, Fri, 21st Oct 2011

Yes, but they smell different. I mean they produce a smell like that of rotting oranges. That would be the best comparison I could make. Not that I know what rotting oranges smell like. Ryan, Sun, 18th May 2014

Today I was wondering why my dog just loves to kick my hands. It occurred to me it wasn't about the licking, is was about the smelling. The up pass gets my hand moist the down pass is the payoff, where he smells all the interesting things his saliva has uncovered. While I'm presenting my theories, here is another. I wondered what the point of the very long hairs on his ears was. I decided they must build up an electric charge then act as an ionization shield for dirt and noseeums that might get into his ears or eyes. I figure that's what all hair that does not warm is for. (Even ours.) Finally I wondered why he wags his tail when he is happy. I figure its not that he is happy, but he wants to send his scent far and wide with his tail fan. If that's correct I'll bet dogs wag their tails after marking their territory. (I have never paid attention.) Gotaudio, Sun, 23rd Nov 2014

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