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Friday, Dec 09, 2022

Explained: How dogs can sniff and tell whether you are stressed

Service dogs, which are trained to provide assistance to people experiencing anxiety, panic attack disorders and PTSD, can detect the psychological alterations associated with these conditions, solely through their odour-detection capabilities

Dogs have more than 100 million olfactory receptor sites, while the number stands at 6 million for humans. (Photo: AP)

Stress is part of everyday life for all and researchers have found that humans produce a distinct odour in stressful circumstances which dogs can detect through their sense of smell.

A newly published study by the Public Library of Science has found that dogs can differentiate between stressful and non-stressful situations by detecting this odour. One of the authors of the research and a PhD student at Queen’s University, Belfast, Clara Wilson, said: “This study has definitely proven that in people, when they have a stress response, their odour profile changes.” This finding can prove useful in training service dogs who support people experiencing post-traumatic stress disorder (PTSD) and help enhance one’s understanding of human-dog relationships.

How does the study define “stress”?

The study considers “stress” as a “physiological and psychological response to a challenging situation (i.e., a stressor) which is exacerbated when an individual does not feel confident in their ability to overcome the stressor”. The term is further categorised as “negative”, when an individual does not have adequate measures to overcome a stressful situation, and “positive”, when an individual possesses adequate resources to overcome a stressful situation. Negative stress is accompanied by an increase in heart rate and blood pressure, whereas, positive stress is often accompanied by a decrease in blood pressure levels.

The study, though refraining from conceptualising stress as an emotion in humans, highlights that negative stress elicits “relatively automatic emotional responses based on an individual’s perception of a stressor”. This response involves the same regions of the brain that are implicated in experiencing fear. Human beings, when stressed or scared, thus experience negative stress, and as demonstrated by the study, produce changes in their odour profiles.

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How do dogs detect human emotions?

While human beings mostly use their vision to assess the world, dogs are believed to use both their sight and smell to perceive and communicate with their surroundings. According to Ryan Llera and Lynn Buzhardt, doctors of Veterinary Medicine at VCA Animal Hospitals, canines have more than 100 million olfactory receptor sites, while the number stands at 6 million for humans. Moreover, the area of the brain responsible for interpreting odours in dogs is around 40 times larger than human beings.

How was the study conducted?

Given the close association of dogs with human beings, it is possible that they detect changes within humans through their sense of smell, beyond what has been found through earlier studies. Breath and sweat samples were obtained, in combination, from thirty-six participants at baseline (starting point), and after inducing them with some levels of stress (by assigning them the task of counting backwards from 9,000 in units of 17). The study was conducted over 36 sessions and in two phases.

A dog was trained in Phase One to detect the stress sample with alert behaviour, by presenting with a participant’s stress sample (obtained immediately after engaging in the stressful task) and two samples without breath and sweat.

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Phase Two involved the stress sample, the baseline sample of the same participant, and a blank sample. The dog’s performance of their alert behaviour on the stress sample was measured.

It was observed that dogs chose the stress sample in 675 out of 720 trials (a combined accuracy of 93.75%). This observation indicates that each participant’s samples were different at baseline and after stress-induction. Moreover, odour control procedures ensured that dogs did not rely on external cues to discriminate between samples. This performance suggests that the baseline and stress odours in human beings are distinguishable.

What is the relevance of this study?

The study claims that this finding is crucial to understanding the ways in which dogs may “interpret, and interact with, human psychological states”. Service dogs, which are trained to provide assistance to people experiencing anxiety, panic attack disorders and PTSD, can detect the psychological alterations associated with these conditions, solely through their odour-detection capabilities — an odour component introduced in the training of dogs can help them detect acute stress responses in their owners.

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What else can canines detect?

The finding that dogs can detect changes in odour profiles of human beings relies on the premise that human beings release volatile organic compounds that are exhaled through their breath, occupy their skin surface, and are found in urine, faeces and saliva. This is further demonstrated in the ability of dogs to detect complex medical conditions in human beings, like cancers of the lung, bladder, prostate, and breast by sniffing breath, urine and stool samples.

Claire Guest, co-founder and chief scientific officer at the charity Medical Detection Dogs, highlights that “the medical alert assistance dogs are being trained to alert people with complex health conditions when they are in danger of having a potentially life-threatening medical event by detecting changes in their odour”.

Besides their nose, Jacobson’s organ (or vomeronasal organ) serves as a unique part of the dogs’ olfactory system, dedicated to chemical communication. Its nerves, different from those that detect ordinary odours, lead directly to the brain and facilitate the detection of “undetectable” odours.

First published on: 30-09-2022 at 01:06:59 pm
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