According to a new scientific study dogs can smell when humans are under stress. Dogs likely pick up on contextual cues from stressed family members (rushing around, loud voices, crying, etc.) but now researchers have discovered they can also smell the stress on their human family members.
In the study, dogs were presented with different human sweat and breath samples — some of the samples came from individuals who just attempted math problems in front of an audience (stressed), and others came from the same group of people before the math challenge (presumably unstressed). More specifically, the samples were taken just four minutes apart from humans who had to count backward from 9,000, using in units of 17, and who had to do so in front of two researchers. Heart rate and blood pressure measurements were also taken, and participants also filled out questionnaires asking about their stress after the fact. (source)
“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 behavior. 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 behavior on was measured.” (source)
“If dogs can correctly alert on the stress sample in Phase Two (when the baseline sample was present), it suggests that baseline and stress odors 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”. (source)
Summary of results: Four of the dogs involved in the study could sniff out the stressed math solver samples, likely picking up the subtle changes stress can have on sweat compounds. Bottom line: in 94% of 720 trials, the dogs were able to correctly alert the researchers to the stress sample.
“…We have shown using a laboratory study that there is a confirmed odor component that is likely contributing to dogs’ ability to sense when we are stressed.”
– Clara Wilson, animal psychologist
Journal reference: Wilson, C., Campbell, K., Petzel, Z. & Reeve, C. Dogs can discriminate between human baseline and psychological stress condition odors. PLoS ONE, 17(9): e0274143. September 28, 2022. https://doi.org/10.1371/journal.pone.0274143