Dogs can detect stress in humans from their sweat and breath, researchers from the Queen's University Belfast in Northern Ireland found.
Published in peer-reviewed journal PLOS One, the study involved four dogs from Belfast and 36 people.
Researchers collected samples of sweat and breath from participants before and after they did a difficult mathematics problem. The participants self-reported their stress levels before and after the task.
Researchers noted that they only used samples where the participant's blood pressure and heart rate had increased.
The dogs were taught how to search a scent line-up and alert researchers to the correct sample. The stress and relaxed samples were then introduced but at this stage, the researchers didn't know if there was an odor difference that dogs could detect.
In every test session, each dog was given one person's relaxed and stressed samples, taken only four minutes apart. All of the dogs were able to correctly alert the researchers to each person's stress sample.
"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," researcher Clara Wilson said, adding that dogs do not need visual or audio cues to pick up on human stress.
Wilson also noted that the "first study of its kind" 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 added.
Helen Parks, the master of a two-year-old Cocker Spaniel named Treo who took part in the study, said the study made her more aware as an owner about her dog's ability to use his nose to "see" the world.
"We believe this study really developed Treo's ability to sense a change in emotion at home," Parks said. "The study reinforced for us that dogs are highly sensitive and intuitive animals and there is immense value in using what they do best—sniffing!" (ANI)
(Editor's note: Minor changes have been made in this republished article.)