Dogs can discriminate between human baseline and psychological stress condition odours

Abstract

Previous research suggests that dogs can detect when humans are experiencing stress. This study tested whether baseline and stress odours were distinguishable to dogs, using a double-blind, two-phase, three-alternative forced-choice procedure. Combined breath and sweat samples were obtained from participants at baseline, and after a stress-inducing (mental arithmetic) task. Participants’ stress was validated with self-report and physiological measures recorded via a Biopac MP150 system. Thirty-six participants’ samples were presented to four dogs across 36 sessions (16, 11, 7 and 2 sessions, respectively). Each session consisted of 10 Phase One training trials and 20 Phase Two discrimination trials. In Phase One, the dog was presented with a participant’s stress sample (taken immediately post-task) alongside two blanks (the sample materials without breath or sweat), and was required to identify the stress sample with an alert behaviour. In Phase Two, the dog was presented with the stress sample, the same participant’s baseline sample (taken pre-task), and a blank. Which sample (blank, baseline, or stress) the dog performed their alert behaviour on was measured. If dogs can correctly alert on the stress sample in Phase Two (when the baseline sample was present), it suggests that baseline and stress odours are distinguishable. Performance ranged from 90.00% to 96.88% accuracy with a combined accuracy of 93.75% (N trials = 720). A binomial test (where probability of success on a single trial was 0.33, and alpha was 0.05) showed that the proportion of correct trials was greater than that expected by chance (p < 0.001). Results indicate that the physiological processes associated with an acute psychological stress response produce changes in the volatile organic compounds emanating from breath and/or sweat that are detectable to dogs. These results add to our understanding of human-dog relationships and could have applications to Emotional Support and Post Traumatic Stress Disorder (PTSD) service dogs.

Can scent-detection dogs detect the stress associated with trauma cue exposure in people with trauma histories? A proof-of-concept study

“…The strong positive correlation between Ivy's performance and the donors' State Anxiety indicates her sensitivity primarily to the SAM axis volatiles. This is consistent with a prior study ( 53 ) which provided evidence of canines' ability to detect human stress volatiles released in mere three minutes (most likely from SAM, not HPA axis). In contrast, Callie may have responded to glucocorticoid-related VOC's (e.g., from cortisol release in the HPA axis).…”

“…Forty pet dogs displayed more stress-related behaviours and arousal (e.g., elevated heart rate) when sniffing pooled samples from the fear vs. joy or control (no human odour) conditions ( 52 ). A third study ( 53 ) collected breath and sweat samples from 36 humans immediately before and after a mental arithmetic task and validated their stress by blood pressure, heart rate, and self-report. The validated samples were then presented to four formerly-trained scent-detection dogs in a three alternative forced choice discrimination task (baseline and stress samples of the same donor, and a blank sample).…”

Scent detection dogs as a novel method for oestrus detection in an endangered species, the Tasmanian devil (Sarcophilus harrisii)

“…When in use, each specimen jar (without lid) containing devil faeces was placed in a separate metal scent pot with a mesh lid to allow dogs to sniff, but not access the source of, the scent. To avoid saliva contamination that could influence the dog’s choice during training, scent pots were sanitised between each dog using 70% isopropanol wipes and allowed to dry before use ( 44 , 45 ), and 2–5 used scent pots were also randomly replaced with clean, unused pots. During assessments, however, clean scent pots were used for each dog.…”

“…During assessments, however, clean scent pots were used for each dog. After each training/assessment day, scent pots were washed in a designated dishwasher (with no detergent) to remove organic material, air-dried, and then sprayed with 70% isopropanol and left to dry ( 44 , 45 ).…”

Horses discriminate human body odors between fear and joy contexts in a habituation-discrimination protocol

“…A few studies have suggested that domestic mammals can perceive our emotions through olfaction and are influenced by them. For example, cattle sniffed human sweat produced in a non-stressful context for longer than that produced in a stressful context 29 , and dogs can distinguish between human odors from baseline and psychological stress conditions 30 . Dogs also showed more stress-like behaviors 25 and interacted less with an unfamiliar human 31 , 32 after sniffing human sweat collected while watching a fear-inducing video rather than a joy-inducing video.…”