Your dog can tell when you’re feeling stressed because you smell different, new research has revealed. So strong is the stench of human worry that the dogs in the study could correctly distinguish between relaxed and stressed odors in 93.75 percent of trials, even when the person involved was a complete stranger.
Researchers recruited four dogs from Belfast in Northern Ireland. Named Treo, Fingal, Soot, and Winnie, the science puppers consisted of one cocker spaniel, one cockapoo, a lurcher-type mixed breed, and a terrier-type mix.
Sweat and breath samples were collected from 36 human participants before and after attempting a fast-paced math problem, with increases in blood pressure and heart rate providing confirmation of elevated stress levels following completion of the task. The four scholarly pooches were then trained to distinguish between baseline and stressed-out samples, identifying the latter by holding their nose close to the sample for five seconds.
Overall, the four dogs correctly discerned the smell of stress in 675 out of 720 trials, with the performance of individual dogs ranging from 90 to 96.88 percent accuracy.
“The findings show that we, as humans, produce different smells through our sweat and breath when we are stressed and dogs can tell this apart from our smell when relaxed – even if it is someone they do not know,” explained study author Clara Wilson in a statement.
According to the researchers, the dogs may have been able to detect the smell of stress hormones like cortisol. They also explain that stress leads to “the stimulation of gluconeogenesis, glycogenolysis, and lipolysis, and increased levels of renin and angiotensin II enzyme,” all of which may also be apparent to dogs.
“The research highlights that dogs do not need visual or audio cues to pick up on human stress,” adds Wilson. “This is the first study of its kind and it provides evidence that dogs can smell stress from breath and sweat alone, which could be useful when training service dogs and therapy dogs.”
“It also helps to shed more light on the human-dog relationship and adds to our understanding of how dogs may interpret and interact with human psychological states,” she said.
The researchers say that future studies may provide greater insights into “emotional contagion” whereby dogs mirror the affective state of their owners. Though the current study did not assess the dogs’ emotional responses to human stress, the authors note that the pets generally became happily excited when they detected these samples, as they came to expect a food reward for a correct alert.
Overall, they say that their findings “could have further applications to the training of anxiety and PTSD service dogs, that are, currently, predominantly trained to respond to visual cues.”
The study was published in the journal PLOS ONE.