As any dog owner would likely anecdotally report, our pet pooches are seemingly able to sense when we are feeling tense and stressed. Now, a group of researchers at Queen’s University Belfast have figured out exactly how they are able to do this: they are able to ‘smell’ stress in our sweat and on our breath.

The finding follows on from previous studies that have shown that dogs can sniff out cancer and COVID-19 in human sweat.

To make the discovery, the team gathered together four dogs from normal domestic homes - Treo, Fingal, Soot and Winnie – and 36 volunteers. They set the volunteers a complicated maths problem designed to up their stress levels and took samples of their sweat and breath before and after they tackled the sums.

Throughout the experiment, the researchers monitored the volunteers and only took the second sample when they detected an increase in blood pressure and a raised heart rate – both clear indicators of stress.

Meanwhile, the dogs were trained to pick out specific scents from a line up.

The team then presented each of the dogs with a selection of scents featuring one of the volunteer’s relaxed sample and stressed sample to see if the dogs could distinguish between them based on scent alone. All four of the dogs were able to correctly alert the researchers to each volunteer's stress sample, even though they had never met them before.

Soot, one of the dogs tested in the study, alerting the researchers to a sweat sample.

Soot, one of the dogs tested in the study, alerting the researchers to a sweat sample. © Queen's University Belfast

“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,” said researcher Clara Wilson, a PhD student in the School of Psychology at Queen’s.

“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.”

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