Dogs can detect stress levels from our breath and sweat

Dogs can distinguish between stressed and relaxed humans based solely on their sweat and breath. The finding could be used to inform service dog training programs. When we are under stress, our bodies undergo a variety of physical changes. Our heart rate increases, we become clammy, and the chemical composition of our sweat and saliva alters. Previous research has demonstrated that dogs can detect fear, covid-19, and cancer in humans. Clara Wilson of Queen's University Belfast in the United Kingdom wanted to know if dogs could detect human stress.

To determine this, she and her team had 36 individuals perform an arduous mathematical exercise. “They had to count backwards from 9000 in chunks of 17 out loud in front of the research panel. And if they got anything wrong, we would interrupt them,” says Wilson. After three minutes, the participants were stopped.

The researchers collected samples of perspiration and breath before and after the physical activity. The volunteers did this by placing gauze on their foreheads and necks, breathing on it three times, and then placing it in a glass vial.

Dogs can detect our stress levels from our breath and sweat.

Within three hours of the exercise, the team used the vials to test four dogs trained to identify a scent match in a lineup. The dogs were given a piece of gauze from the participant taken after the task and instructed to find a match from three vials containing gauze from the participant before the task, gauze from the participant after the task, and a blank piece of gauze. In 675 out of 720 tests, or approximately 94% of the time, the dogs correctly identified the stressed sample from the lineup.

According to Juliane Brauer of the Max Planck Institute in Germany, the ability may have originated from our long history of canine companionship. “Maybe other animals can also distinguish a stressed human, but they wouldn’t care,” she says.

Wilson hopes that the discovery will inform the training of service dogs that assist individuals with panic attacks or post-traumatic stress disorder, as these dogs are currently trained primarily on visual and body posture cues. Dogs could be taught to detect changes in their owner's scent, which may be present even in the absence of visible signs of stress. Wilson then wants to investigate whether canines can detect other emotional states—including happy ones—via sweat and breath.

Journal reference: PLoS ONE, DOI: 10.1371/journal.pone.0274143