The physiological processes related to an acute psychological stress response produce changes in human breath and sweat that dogs can detect with an accuracy of 93.75%, in keeping with a recent study published this week within the open-access journal PLOS ONE by Clara Wilson of Queen’s University Belfast, UK, and colleagues.

Odors emitted by the body constitute chemical signals which have evolved for communication, primarily inside species. Given dogs’ remarkable sense of smell, their close domestication history with humans, and their use to support human psychological conditions resembling anxiety, panic attacks and post-traumatic stress disorder (PTSD), researchers wondered whether dogs might be sensing chemical signals to reply to their owners’ psychological states.

In the brand new study, the researchers collected samples of breath and sweat from non-smokers who had not recently eaten or drank. Samples were collected each before and after a fast-paced arithmetic task, together with self-reported stress levels ​and objective physiological measures: heart rate (HR) and blood pressure (BP). Samples from 36 participants who reported a rise in stress due to the task, and experienced a rise ​in HR and BP ​through the task, were shown to ​trained dogs inside three hours of being collected. 4 dogs of various ​breeds and breed-mixes had been trained, using a clicker in addition to kibble, to match odors in a discrimination task. At testing, dogs were asked to seek out the participant’s stress sample (taken at the top of the duty) while the identical person’s relaxed sample (taken only minutes before, prior to the duty starting) was also within 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 probability (p<0.001). The primary time they were exposed to a participant's​ stressed and relaxed samples, the dogs appropriately ​alerted to the stress sample 94.44% of the time. Individual dogs ranged in performance from 90% to 96.88% accuracy.

The authors conclude that dogs can detect ​an odor related to the change in Volatile Organic Compounds produced by humans in response to emphasize, a finding that ​tells us more in regards to the human-dog relationship and will have applications to the training of hysteria and PTSD service dogs which are currently trained to reply predominantly to visual cues.

The authors add: “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 in a position to detect this variation in odor.”

Source:

Journal reference:

Wilson C, Campbell K, Petzel Z, Reeve C (2022) Dogs can discriminate between human baseline and psychological stress condition odours. PLoS ONE. https://doi.org/10.1371/journal.pone.0274143