Dogs Smell Human Fear and Mirror Our Mood When They Do

A recent study shows what many have “known” about the power of a dog's nose
By Mark Bekoff, November 2017

A dog's nose knows.

A dog's nose is a work of art, an organ that's evolved to be an incredibly sensitive to a wide variety of odors. Dogs put their noses in all sorts of places, many of which we find disgusting or offensive but that's what it's like to be a dog and we have to accept that's how they sense their world. Not allowing dogs to sniff can be seen as a form of sensory deprivation that robs them of vital information they need to navigate their surroundings including odors from the mouth, ears, and other areas of the body including those very special private parts of other dogs, other animals, humans, and yes, pee, poop, and a wide variety of stinky stuff they crave and savor and we find utterly revolting. 

It always surprises me when I talk with people about dog behavior and what they think is well known and supported by scientific research. One phrase I often hear goes something like, "Dogs smell our moods, especially fear, and they too get leery and uneasy." I catch myself sometimes saying this to people, but I realize that we don't really "know" this from any sort of scientific research. However, a good deal of citizen science has clearly alerted me and others that this could be something real.

It's always good when our intuitions are supported by research, and a new study conducted by Biagio D’Aniello and his colleagues published in the journal Animal Cognition called "Interspecies transmission of emotional information via chemosignals: from humans to dogs (Canis lupus familiaris)" confirms what many have "known," namely that dogs do smell human fear using chemosignals and they too get scared. The original research report isn't available online, but an apt summary and a complete list of references are provided. 

Dr. D’Aniello and his team studied Golden retrievers and Labradors and were interested if human body odors, called chemosignals, produced in the armpits of happy and fearfulmale humans, could be detected by the dogs and how the different odors affected the dogs. During the experiment, the dog's human ("owner"), a strange human, and an odor dispenser were present in a room where the dogs could move around freely. The three sweaty odors represented fear, happiness, and a control situation in which there was no sweat. The researchers studied how the dogs interacted with their owner, the stranger, and the sweat dispenser and monitored the dog's heart rate. 

Their results can be summarized as follows: "There were fewer and shorter owner directed behaviors and stranger directed behaviors when they were in the 'happy odor condition' compared to the fear odor and control conditions. In the fear odor condition, they displayed more stressful behaviors. The heart rate data in the control and happy conditions were significantly lower than in the fear condition. Our findings suggest that interspecies emotional communication is facilitated by chemosignals."

I hope that the complete research paper will soon be available online, but a very useful summary of this research project is provided by Jake Buehler in an essay published in New Scientist titled "Dogs really can smell your fear, and then they get scared too." He writes, "Dogs exposed to fear smells showed more signs of stress than those exposed to happy or neutral smells. They also had higher heart rates, and sought more reassurance from their owners and made less social contact with strangers." 

All in all, the results of this study add to data that show that dogs and humans communicate very well using different senses (for further discussion please see "Dogs Are More Expressive When We're Looking at Them," "Do Dogs Really Manipulate Us? Beware Misleading Headlines," and links therein). What I really like about Dr. D’Aniello's stay is its simplicity. I can well imagine people trying to do a similar study at home or on a walk or at a dog park. This would be a good way to further connect with the dog(s) with whom one shares their home and heart. It could also be enriching to the dog, and the results also could show how different dogs respond to various odors given their unique personality. The dogs with whom I shared my home showed distinctly different responses to different odors. Such "citizen science" can motivate further systematic and more controlled research. 

Let dogs sniff and let's not hijack one of their vital connections to the world at large

I'm very pleased to learn that what many have already "known" is well supported by systematic research. I wonder, and sometimes worry, as do many others, how the use of different smelly "dog" and "human" products such as shampoos, soaps, and deodorants mask what dogs are able to sniff in their surroundings and also mask what we're feeling. Mr. Buehler notes that it's possible for humans to hijack their dog's emotions. 

I'm sure many others, as have I, have seen a dog respond to novel and unnatural odors by keenly sniffing them and seemingly wonder what in the world is going on, or by avoiding them all together. I well remember one of the dogs with whom I lived, Jethro, seeing and then running up to his close friend Zeke, and when Jethro was about five feet away from the dog he knew was Zeke, he suddenly and rapidly stopped using all four feet as brakes, cocked his head from side-to-side and lifted his nose as if to say something like, "I know you're Zeke but you don't smell like him." Jethro seemed to be utterly confused. It turns out Zeke had had a bath that morning (much-needed indeed after rolling in some stinky goopy stuff) and Jethro just had to be sure Zeke was Zeke and all was okay. 

Being smell-blind can be aversive to dogs. My recommendation is to let dogs sniff and let's not hijack one of their vital connections to the world at large. Let them sniff to their nose's content when they're tethered on a leash or when they're walking and hanging out with friends and others and running freely. As mentioned, not allowing dogs to exercise their nose and other senses could be a form of sensory deprivation that robs them of information they need to figure out what's happening in their world. Being smell-blind can indeed be stressful to dogs because they need odors and other information to assess what's happening around them. 

Please stay tuned for more research on the cognitive and emotional lives of dogs and other animals. It's an exciting time to do this sort of research and to learn more about what they're thinking and feeling, how they sense and process information coming in from other animals and their environment, and what's going on in their heads and in their hearts.

Learning more about the cognitive and emotional lives of dogs is good for them and good for us. This information can be used to foster respect for who they are as individuals and to develop and to maintain strong and enduring social bonds, a win-win for all. 

This was originally published in Psychology Today and used with permission.

Marc Bekoff is a professor in the Department of Ecology and Evolutionary Biology, University of Colorado, Boulder. All of this material is discussed in his book, The Emotional Lives of Animals: A Leading Scientist Explores Animal Joy, Sorrow, and Empathy ñ and Why They Matter (New World Library 2007). He blogs for Psychology Today.