Smell This!

Dogs smell things. A lot of things. A lot of the time. Their noses are very important to them.

Dog Nose

And, most dog folks would agree that the dog’s nose is a pretty amazing sense organ. Indeed, we capitalize on our dogs’ olfactory (smellin’) acuity when we train them to select scent articles in Utility training, follow a missing person’s trail, find contraband and other nasty stuff in public places, and even detect the presence of cancer in human patients. Research in recent years has shown us that the dog’s impressive smelling abilities are due to a number of pretty cool physical adaptations:

  1. LOTS OF CELLS: Dogs have hundreds of millions of olfactory receptor cells lining the inside of their nose; many times more than the number found in the human nose. This difference contributes to their ability to detect almost impossibly minute concentrations of compounds.  This large number of canine olfactory cells is enough to cause smell envy in any dull-nosed human.   
  2. BIG BRAIN: Two parts of the dog’s brain that interpret incoming information from the nose are the olfactory bulb and the olfactory cortex. Both of these areas are highly developed in dogs and are important for how dogs use the sensory information that the nose provides.
  3. SNIFF SNIFF: Dogs sniff. We don’t. Sniffing involves a disruption of the dog’s normal breathing pattern  and functions to enhance a dog’s ability to detect and differentiate smells. Here is what we currently understand about sniffing: First, as the dog inhales during a sniff, the air is diverted into several flow paths. This partitioning effectively increases the number of sensory cells within the nose that inhaled components are exposed to, increasing olfactory sensitivity. Then, during the exhale phase of the sniff, the air leaves via the dog’s “side-nostrils”, not out the front of the nose as it does with normal breathing.  (So that’s what those slits in the side of my dog’s nose are for! Who knew?). Exhaling through the “side nose” is presumed to prevent the dog’s sensory cells from being repeatedly exposed to the same compounds, thus slowing the process of scent habituation. (Consider how you no longer can smell “wet dog” after being around it for a while; that’s scent habituation).

Sniffing Dog

Choice by Smell: Recently, researchers at Barnard College’s Dog Cognition Lab asked a broad question about the dog’s olfactory ability: “How do pet dogs use their nose to make decisions and choices in their every day lives?”.  Alexandra Horowitz, Julie Hecht and Alexandra Dedrick began this series of studies  by first asking if dogs have the ability to discriminate between large and small concentrations of smells (1). This question was of interest because previous work has shown that, similar to many primate species, dogs can visually discriminate between different quantities of food (2). It follows that, since the dog’s nose is so spectacularly talented, that they would be at least equally capable of the same type of choice using their noses. Here is a summary of their recently published study:

Study Design: A group of 69 pet dogs (and their people) were recruited for the study. Following some initial pre-training, dogs were presented with two covered plates, equidistant apart. One plate held a single chunk of hotdog. The second, the motherload plate, held five chunks of hotdog.  In the first trial, dogs were given no guidance at all from their owner and were allowed to choose one of the two plates. In a second trial, designed to test for the effects of social cues, the owner showed a clear preference for the plate holding the single piece of food before their dog was allowed to make his or her selection.  (These procedures were quite involved and are described in detail in the paper).

cupcake-dogI’m pretty sure this is the BIGGEST cupcake!

Results: There are actually a number of interesting findings (and additional questions) reported in this paper. For brevity, I will focus on two that I found to be especially relevant:

  1.  First: The dogs in this study, who were pet dogs that had no previous training in any type of scent detection or scent following work, did not demonstrate an ability to discriminate a “small quantity” from a “large quantity” of food using only their sense of smell. This result is surprising, since dogs do seem to have this ability when tested using vision and considering what we know about dogs’ highly developed olfactory acuity.
  2. Second: When dogs’ owners showed a clear preference for the plate that held the smaller quantity of food, the dogs did show a significant preference  – for the plate with the smaller quantity! In other words, dogs were readily and easily influenced by the social cues provided by their owners regarding which plate to choose. This result was in agreement with the visual preference study – dogs of owners who pointed at a plate that clearly contained the smaller pile of food were more likely to choose that plate over the plate whose food runneth over!

Conclusions: The authors of this study suggest that our dogs, living in a human-centered environment, may not always be using their noses to the extent of their actual ability. Perhaps when making decisions in everyday life dogs learn to depend too heavily upon social cues from their human companions, to the extent that they ignore information from their own senses.

Take Away for Dog Folks: The results from this study led me to think about how we live with our dogs and how we may unwittingly discourage them from using their noses on a daily basis.  Maybe, by caring for our dogs so well, and making so many of their decisions for them (what to eat, when to eat, how much to eat, what plate to choose), we influence a bit too much and unintentionally inhibit one of their most amazing and enviable talents. For example, at my training school we teach “Leave it“, a command that can keep dogs safe when they decide to investigate something that may be dangerous to them. However, when we ask for this behavior, are we  unintentionally inhibiting dogs’ use of (and enjoyment of) their nose? Just a thought. Personally, I still will always teach this response to my dogs (and those of my students) because it is truly  an invaluable behavior to train for its safety and control utility. However, reading this study has encouraged me to consider a bit more carefully each of the everyday circumstances in which I use it.

Consider also the currently popular K-9 Nose Work classes. Almost uniformly, reports about these scent work games are that dogs, (all dogs, regardless of their level of previous training, age, or athletic ability) LOVE, LOVE, LOVE  K-9 Nose Work and the success that they experience when encouraged to use their nose and search independently. Perhaps these classes are unleashing some of that latent “nose power” that all dogs have and that they may not always be encouraged to use when living in a typical anthropocentric (human-centered) world. So, Kudos to all of you who encourage your dogs to smell, sniff, find (safe) stuff, and who play nose games with your dogs, teach them to track, or simply regularly encourage them to “SMELL THIS!”

Big Nose


  1.  Horowitz A, Hecht J, Dedrick A: Smelling more or less: Investigating the olfactory experience of the domestic dog, Learning and Motivation 2013; 44:201-217.
  2. Prato-Previde E, Marshall-Pescini S, Valsecchi P: Is your choice my choice? The owner’s effect on pet dogs’ (Canis lupus familiaris) performance in a food choice task. Animal Cognition 2008; 11:167-174.

Excerpted from Linda Case’s book “Beware the Straw Man: The Science Dog Explores Dog Training & Fiction

Beware Straw Man Cover

13 thoughts on “Smell This!

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  4. I’m really enjoying your blog, it’s great to have sicence explained to us laymen, so thanks. I’ve always wondered about the vision vs scent preference in dogs. I understand and agree that dogs have amazing scenting abilities but in my own experience I’ve seen dogs ignore what their nose’s were telling them and believe what their eyes were saying.


    • Hi Mary! I agree and this is something that I think is truly fascinating. I do wonder how much of their reliance upon their eyes comes from living with humans and learning from us about pointing (visual) at things, using hand signals, etc. I will look for more studies about this phenomenon as the “Smell This” piece generated a lot of interest. Keep an eye on Julie Hecht’s work and her blog in Scientific American!


  5. Great article. The downside (or upside if you are a practicing veterinarian) of this “Hoover” activity is the ability to suck up particles, pieces of grass, etc. that may take days of sneezing to eliminate. Here in California we constantly remove foxtails that get lodged in the nose due to Fido’s nasal fixation.
    Love your blog.


    • Hi Ken, Thanks! And, a great point about dogs inhaling things that should not be inhaled during our dogs’ nasal wanderings. Here in the Midwest we do not have foxtails (thank goodness, as I hear they are awful), but instead worry about Blastomycosis. I especially worry when I see my dogs snorting around disturbed soil or if we have had a lot of recent rain…..(over-protective mom in me….). It is such a challenge to strike a good balance between providing good care and keeping our dogs safe, while still allowing them to have fulfilling, dog-centric lives, isn’t it? Linda


  6. You might wish to mention the vomernasal organ–a well-developed scent organ located underneath the nasal septum. Vestigial or non-existent in humans, the VNO is well-developed in dogs. (Adams & Weikamp, Jour. Anat., 1984).

    The VNO senses non-volatile scent sources (the scent is not airborne). Some researchers believe that the VNO is especially related to behavior that results from pheromones, particularly sexual and aggressive behavior.

    I suppose this accounts for some canine behavior: licking stuff. It brings the scent information to the VNA.


  7. I always allow Max plenty of time to smell things on our walk. When I say “okay, go sniff” he knows it means I will follow his lead (as long as he is not pulling on the leash). So we do some heeling (very little), some loose-leash walking where I decide which way we go, and lots of “sniffing” on our walks. We usually walk about an hour at a pretty leisurely pace 🙂


    • Love this! We encourage our students also to do this with their dogs (and many seem surprised as they are indoctrinated into thinking that dogs should never deviate from heel when out walking). Ian Dunbar uses the phrase “life rewards”, which can be a nice way to do it. Alternatively, perhaps we should just look at it as allowing our dogs to be dogs, rather than having it be part of training! It sounds like you have a lovely balance with your Max! Linda


  8. So interesting, thanks for summing up the recent olfactory study as well! I play dog cognition games using scent and sight, similar to what they did in the trial, and I’ve found the same thing, that he’s not using his nose, he’s using us or his vision. Usually his vision overrides us (ie we show him how we loaded one upside cup with heaps of treats and the other cup with one treat) when we tell him to get that cup with one treat, he’ll go to the other that he knows has more food. He seems to rely on vision, then us, then his nose, in that order…… I completely agree, what are we doing to them when they aren’t living by their noses anymore?!


    • Hi Erin, Interesting that you see the same patterns with your boy. I have loved reading about what many folks do with their own dogs to encourage independent use of their senses – and how much the dogs truly love it! I find it especially interesting that visual cues appear to dominate in many dogs and wonder if that is influenced to some degree by social learning from living in our human-centered world with us. Thanks for writing and for following! Linda


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