Dog can smell the changes in our breath and sweat that occur when we’re stressed, according to new research by scientists from Newcastle University and Queen’s University Belfast.
Odors emitted by the body constitute chemical signals that have evolved for communication, primarily within species.
A sense of smell of dogs and other canines provides critical information, essential for being aware of potential predators, locating food, identifying conspecifics, and enabling recognition of familial members.
Research on chemical signals has extended to explore inter-specific communication, such as that between mice and humans, cows and humans, horses and humans, and canines and humans.
Given domestic dogs’ remarkable sense of smell, and their close domestication history with humans, it is possible that they are detecting odors associated with changes within the human body beyond those that have already been established.
The use of dogs to support human psychological conditions such as anxiety, panic attacks and post traumatic stress disorder (PTSD) is growing in popularity, with waiting lists for PTSD service dogs being months-to-years long in some instances.
Such dogs have been reported to improve an individual’s quality of life, social connections, and reduce the number of panic attacks or PTSD symptoms, with the tasks of ‘calming’ and ‘interrupting anxiety’ reported as the most helpful part of their behavioral repertoire.
However, empirical evidence for what mechanisms dogs may be utilizing to respond to their owner’s psychological experience is currently lacking.
“Our 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 lead author Clara Wilson, a Ph.D. student in the School of Psychology at Queen’s University Belfast.
In the study, Wilson and colleagues collected samples of breath and sweat from non-smokers who had not recently eaten or drank.
Samples were collected both before and after a fast-paced arithmetic task, along with self-reported stress levels and objective physiological measures: heart rate (HR) and blood pressure (BP).
Samples from 36 participants who reported an increase in stress because of the task, and experienced an increase in HR and BP during the task, were shown to trained dogs within three hours of being collected.
Four dogs of different breeds and breed-mixes — Treo, Fingal, Soot and Winnie — had been trained, using a clicker as well as kibble, to match odors in a discrimination task.
At testing, dogs were asked to find the participant’s stress sample (taken at the end of the task) while the same person’s relaxed sample (taken only minutes before, prior to the task starting) was also in the sample line-up.
Overall, dogs could detect and perform their alert behavior on the sample taken during stress in 675 out of 720 trials, or 93.75% of the time, much greater than expected by chance.
The first time they were exposed to a participant’s stressed and relaxed samples, the dogs correctly alerted to the stress sample 94.44% of the time. Individual dogs ranged in performance from 90% to 96.88% accuracy.
“Dogs can detect an odor associated with the change in volatile organic compounds produced by humans in response to stress, a finding that tells us more about the human-dog relationship and could have applications to the training of anxiety and PTSD service dogs that are currently trained to respond predominantly to visual cues,” the authors said.
“This study demonstrates that dogs can discriminate between the breath and sweat taken from humans before and after a stress-inducing task.”
“This finding tells us that an acute, negative, psychological stress response alters the odor profile of our breath/sweat, and that dogs are able to detect this change in odor.”
The study was published in the journal PLoS ONE.
C. Wilson et al. 2022. Dogs can discriminate between human baseline and psychological stress condition odours. PLoS ONE 17 (9): e0274143; doi: 10.1371/journal.pone.0274143
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