Dogs are well known for detecting drugs and explosives through their sense of smell, but a new study has found that they can also identify when a person is under stress by smelling their sweat and breath.
According to scientists, this ability could be useful in training assistance dogs for patients.
Researchers asked 36 people to solve difficult mathematics problems and collected samples of their sweat and breath before and after the test.
Each participant also reported how stressed they felt before and after the test. Scientists only used samples from individuals whose blood pressure and heart rate increased during the task.
The study found that dogs do not need to see or hear humans to detect stress—they can identify it purely through smell.
When the samples were presented to four dogs (named Treo, Fingal, Soot, and Winnie), they successfully distinguished the stress-related samples with high accuracy.
Clara Wilson, a PhD student at the School of Psychology at Queen’s University Belfast, Ireland, said: “This discovery shows that when humans are under stress, they release different types of odors through sweat and breath, which dogs can detect—even if they are unfamiliar with the person.”
She added: “This research shows that dogs do not need to see or hear a person to assess their level of stress.”
“This is the first study of its kind and provides evidence that dogs can detect stress through breath and sweat alone, which could be useful in training medical assistance dogs.”
“It also sheds light on the relationship between humans and dogs and improves our understanding of how dogs can interpret and interact with human psychological states.”
One of the dogs involved in the study was a two-year-old cocker spaniel named Treo, who performed exceptionally well.
His owner, Helen Parks, said: “As dog owners, we were both happy and curious that he was taking part in the study because his livelihood is based on smell. We eagerly waited for the results. He is always happy to see the scientists at Queen’s University and quickly learned how the experiment worked.”
“This research shows us even more about dogs’ ability to ‘see’ the world through their noses. We believe it has also improved Treo’s ability to understand emotions at home.”
“This study reinforces that dogs are highly sensitive and intuitive animals, and there are great benefits in using them for scent-based work because they are experts at it.”
In the study, dogs were trained to identify scent-based objects and signal scientists when they detected them.
After this, stress and non-stress samples were presented to them. The scientists did not know whether the dogs would be able to distinguish between the scents. In each test, every dog was given a relaxed sample and a stressed sample from the same person, collected just four minutes apart. All dogs correctly identified the stress-related samples.
The research was published in the journal PLOS ONE.
