Dogs Can Smell When Humans Are Stressed
Dogs can sniff out whether a human is stressed or relaxed, new research suggests, and that sensory feedback appears to influence canine emotions and choices.
The dog doesn't even have to know the human well to interpret odor in this way, the British researchers noted.
“Dog owners know how attuned their pets are to their emotions, but here we show that even the odor of a stressed, unfamiliar human affects a dog’s emotional state, perception of rewards and ability to learn," said study author Dr. Nicola Rooney. She's a senior lecturer in wildlife and conservation at Bristol Veterinary School in Bristol, England.
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"Working dog handlers often describe stress traveling down the lead, but we’ve also shown it can also travel through the air," she said in a University of Bristol news release.
Her team published its findings July 22 in the journal
Scientific Reports.
As the Bristol team noted, research has long pointed to scent as an important but perhaps under-appreciated form of emotional communication between people.
Rooney's group wondered if dogs, with olfactory senses that are so much more sophisticated than humans, might catch human emotions through smell, as well, and act accordingly.
They constructed an elaborate experiment to find out. First, they trained dogs in a simple task: If a bowl was placed in one location, it invariably contained food. But if it was placed in a separate location, no food was present.
For obvious reasons, the dogs soon became more eager to trot over to bowls in the "have" spot than the "have not" location.
But what if the bowl was placed between these locations?
If the pooch ambled quickly over to this ambiguous, mid-range bowl, the researchers considered that the dog was in an "optimistic" frame of mind ("maybe there's food in that bowl!").
If the dog was more hesitant about heading towards the bowl, that reflected a more "pessimistic" attitude ("The bowl's in the wrong spot, probably no food there").
Next, the 18 dogs recruited for the experiment were exposed to sweat and breath samples from humans who'd been in either a stressed or relaxed state of mind (a math test versus listening to soothing music).
When dogs smelled the "stressed" human odors, they were visibly less eager to head towards the ambiguously placed bowl, suggesting an emotional downturn towards pessimism, the researchers said.
"This ‘pessimistic’ response reflects a negative emotional state and could possibly be a way for the dog to conserve energy and avoid disappointment," the researchers reasoned.
However, this "downer" effect was not seen when the dogs were exposed to a "relaxed" odor sample from a human.
According to Rooney, the new findings have real-world applications.
"Understanding how human stress affects dogs' well-being is an important consideration for dogs in kennels and when training companion dogs and dogs for working roles such as assistance dogs," she said.
