Can dogs tell when you’re stressed? New study reveals how they use sense of smell to ‘see’ the world

Dogs have been used to detect drugs and explosive devices for decades, but a new study has suggested they can also sniff out stress from human sweat and breath.

Researchers collected samples of sweat and breath from 36 people before and after they undertook a difficult maths problem.

Each of the participants reported their stress levels before and after the task, and researchers only used samples where the person’s blood pressure and heart rate had increased.

When presented with samples, all four dogs taking part - Treo, Fingal, Soot and Winnie - correctly identified the stress specimens.

The skill could be useful when training service dogs and therapy dogs, according to the scientists.

Clara Wilson, a PhD student in the School of Psychology at Queen’s University Belfast, said: “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.

“The research highlights that dogs do not need visual or audio cues to pick up on human stress.

“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.”

In the study - published in the Plos One journal - the dogs were taught how to search a scent line-up and alert researchers to the correct sample.

Stress and relaxed samples were then introduced, but at this stage the researchers did not know if there was an odour difference the dogs could detect.

In each test session, each dog was given one person’s relaxed and stressed samples, taken only four minutes apart, with all of the dogs able to correctly alert the researchers to each person’s stress sample.

One of the dogs that took part in the study was Treo, a two-year-old cocker spaniel.

His owner, Helen Parks, said: “As the owner of a dog that thrives on sniffing, we were delighted and curious to see Treo take part in the study.

“We couldn’t wait to hear the results each week when we collected him.”

Ms Parks added that the study “made us more aware of a dog’s ability to use their nose to ‘see’ the world” and that it “really developed Treo’s ability to sense a change in emotion at home”.

She 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.”