Is That...Stress Your Dog Smells?

If you’ve ever tried to hide treats from your dog, you know they can sniff out chicken, steak, hot dogs, peanut butter, and even a small bit of cookie stuck in the fold of your sweater. Trying to hide anything with an odor from our dogs is pointless. Turns out, one of those things is our stress, and yes, dogs can smell that, too. 

Clara Wilson, an assistance and working dog researcher at Animal Behaviour Centre, School of Psychology in Belfast, United Kingdom, is the lead author of the recent study, “Dogs can discriminate between human baseline and psychological stress condition odours” in the journal PLOS ONE. She shared in an email: “We wanted to answer a definitive question: Can dogs tell the difference between two samples [of breath and sweat] from the same person before and after becoming stressed?”

She has a background in bio-detection dogs — the ones trained to search samples for human health conditions including cancer, Parkinson’s disease and COVID-19 — but notes: “Whether dogs’ capabilities extend to detecting odors associated with psychological states has been explored far less.” 

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For the sake of science, the 36 people who volunteered to participate in the experiment wiped gauze over the back of their neck, put that gauze into a glass vial, and then exhaled into the vial before sealing it. Next, the experimenters purposefully stressed out the participants, who then put another sample of their sweat and breath into a different vial. 

The source of the stress? Doing math in public. Specifically, they were asked to count down out loud, from 9,000, by increments of 17, for three minutes without the use of pen and paper. If they gave a correct answer, nobody said anything, but they were called out for making a mistake. Bringing back memories of timed math tests and making you sweat? Thought so.

The dogs in the study were pet dogs trained by the researchers to give an alert behavior in response to the scent they were supposed to find. The alert behavior — freezing above the correct sample or sitting down in front of it — allowed the dogs to communicate their ability to tell the odors apart. Wilson shares that she “became very close to the study dogs,” who were pet dogs volunteered by their owners from the local community.

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The dogs had to choose the odor sample given by a person after experiencing stress from a set of samples that also included the baseline sample from that same person, and a “blank” which was a vile containing the kind of gauze used to collect the samples. Based on chance alone — if the dogs were simply guessing — they should have identified the correct odor 33.33 percent of the time. In the experiment, they identified the correct sample 93.75 percent of the time. That means they can distinguish the odor of a person when they are feeling fine from the odor of that same person when they are stressed. 

Wilson told The Wildest: “I was still surprised the first time the dogs were shown the pre- and post-math task samples and confidently discriminated between them. I truly didn’t know if the dogs would interpret these smells as the same, as they had been taken from the same person within four minutes of each other, so it was fascinating to see how accurate the dogs were at discriminating between these odors when the only difference was that a psychological stress response had occurred.”

It’s wild to think that dogs can detect the difference in our body chemistry in stressed and unstressed conditions. “Confirming an odor component to psychological stress may raise further discussion into scent-based training for PTSD or psychiatric service dogs, who are currently often trained to respond to visual signs of distress,” Wilson says.

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It makes sense to train dogs to offer soothing behaviors in response to odors associated with stress. Possibilities include asking for pets, offering physical contact, initiating play, or asking to go for a walk. According to Wilson, training service dogs to respond to odor “could also enhance the reaction time of the alert, if the dog is able to respond to the initial onset of the stress response, as opposed to visual signs of distress that may come minutes later.” 

Wilson believes “more research is needed on dogs’ ability to discriminate between different emotions, such as stress, fear, and excitement.” Luckily, she will continue to have the best partner she could ask for as she continues her work. “I have a very sweet Red Fox Labrador called Eddie, who is four years old. He loves to do scent games and is a good sport when I want to try out new training ideas or concepts for future discrimination paradigms at home.“