Study demonstrates dogs can detect the smell of human stress

Having been domesticated many thousands of years ago, dogs have evolved to become highly attuned to human behavior, but a study has taken this concept into new terrain. The authors conducted experiments to explore whether canines can detect increasing levels of stress in people through their incredible sense of smell, with the results indicating that indeed they can, even if it's someone they are unfamiliar with.

Led by scientists at Queen’s University Belfast, the study is described as the first of its kind and saw four pet dogs enlisted and trained to distinguish between different odors. Thirty six human participants were then subjected to arithmetic tasks designed to induce a stressful state, and were made to wipe gauze on the back of their necks and breathe onto it, both before and after the test.

This produced “stressed” samples for the dogs to try and distinguish from “relaxed” ones, along with perfectly clean ones for controls. In a preliminary experiment, the dogs were first rewarded for distinguishing the stressed samples from the clean ones. The relaxed samples were then introduced, with the dogs made to discriminate between them over the course of 720 trials.

Impressively, the dogs correctly chose the stress sample 94% of the time. The scientists consider this “firm evidence” that stressful states can lead to particular odors, and that dogs can distinguish those odors from the ones we emit when we’re relaxed.

“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 study author Clara Wilson.

The scientists do note that the study didn't test whether dogs perceive stress as positive or negative, and that in real-life scenarios they likely gauge this through other cues, such as our tone of voice or breathing. They do, however, imagine the knowledge proving valuable in the training of service dogs that currently rely largely on visual cues.

“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,” said Wilson. “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.”

The research was published in the journal PLOS One.

Source: Queen’s University Belfast, The Conversation