HALIFAX, Nova Scotia — Post-traumatic stress disorder, or PTSD, is a mental health condition that can develop after a person experiences or witnesses a traumatic event, such as combat, assault, or a natural disaster. People with PTSD often struggle with intrusive memories, hypervigilance, avoidance of trauma reminders, and negative changes in mood and thinking. These symptoms can be debilitating, interfering with relationships, work, and overall quality of life. While traditional treatments like therapy and medication can be effective, some people with PTSD turn to an unexpected source of support: service dogs.
These specially trained dogs are paired with individuals to help them manage their symptoms and improve their daily functioning. One way service dogs may assist their handlers is by alerting them to early signs of distress, such as a racing heart or trembling hands, before an episode of anxiety or a flashback fully takes hold.
But what if dogs could detect the onset of these episodes even earlier, before physical symptoms appear? A groundbreaking new study by researchers at Dalhousie University in Canada suggests that this may indeed be possible – through the power of scent.
The study, published in the journal Frontiers In Allergy, investigated whether dogs could be trained to discriminate between breath samples collected from individuals with trauma histories during two different states: a relatively relaxed state (baseline) and a state of induced stress designed to mimic the distress experienced during a PTSD episode.
The researchers recruited 26 participants who reported experiencing at least one traumatic event in their lives. They collected breath samples from these participants at baseline and again while they were exposed to cues related to their personal traumatic experiences, either through an interview or while undergoing brain imaging.
Two dogs, Ivy and Callie, were then trained to distinguish between the baseline and stress breath samples. In a series of experiments, the dogs were presented with breath samples and asked to indicate which one corresponded to the stress condition.
Remarkably, both dogs were able to correctly identify the stress samples with high accuracy. In the first experiment, where dogs were presented with both a baseline and stress sample from the same participant and asked to choose the stress sample, Ivy and Callie performed with approximately 90% accuracy. This suggests that the participants’ breath indeed changed in detectable ways when they were experiencing distress.
In the second experiment, the dogs were presented with only one sample at a time and had to indicate “yes” or “no” as to whether it was a stress sample. Despite the increased difficulty of this task, Ivy and Callie still performed significantly above chance, demonstrating their ability to generalize the scent of stress across different individuals.
Interestingly, the dogs’ performance did not depend on whether the participant had been diagnosed with PTSD or on the severity of their symptoms. Rather, it was most strongly related to the participant’s self-reported level of distress during the stress condition. This suggests that the dogs were indeed detecting signals associated with the acute stress response, rather than a scent profile specific to PTSD.
So what could these signals be? The researchers speculate that the dogs may have been picking up on volatile organic compounds (VOCs) released during the activation of the body’s stress response systems. When a person experiences stress, their body releases a cascade of hormones like adrenaline and cortisol, which can alter the composition of their breath.
Different stress hormones are released at different stages of the stress response. Adrenaline, for example, is released almost immediately, while cortisol levels may not peak until 10-30 minutes later. The fact that Ivy’s performance was strongly correlated with participants’ self-reported anxiety (which is associated with a rapid adrenaline response) suggests that she may have been particularly sensitive to early-phase stress signals. Callie, on the other hand, showed sensitivity to participants’ levels of self-conscious emotions like shame, which have been linked to cortisol release, suggesting she may have been detecting later-phase stress VOCs.
“Although both dogs performed at very high accuracy, they seemed to have a slightly different idea of what they considered a ‘stressed’ breath sample,” said study first author Laura Kiiroja, of Dalhousie University, in a media release. “We speculated that Ivy was attuned to sympathetic-adreno-medullar axis hormones (like adrenaline) and Callie was oriented to the hypothalamo-pituitary-adrenal axis hormones (like cortisol). This is important knowledge for training service dogs, as alerting to early-onset PTSD symptoms requires sensitivity to sympathetic-adreno-medullar axis hormones.”
The idea that dogs can smell stress is not new. Previous studies have shown that dogs can distinguish between sweat samples collected from people during stressful and non-stressful situations. However, this is the first study to demonstrate that dogs can detect stress VOCs in breath, and the first to link this ability to real-world experiences of distress in people with trauma histories.
If replicated, these findings could have important implications for the training and use of service dogs for PTSD. By teaching dogs to recognize the earliest possible indicators of distress, it may be possible to intervene and prevent the escalation of symptoms before they become overwhelming. This could give handlers more time to employ coping strategies and potentially avoid or minimize the impact of flashbacks, panic attacks, or other acute episodes.
Of course, much more research is needed before this approach can be widely implemented. Future studies will need to confirm these results with larger samples, more rigorous methods for verifying participants’ stress levels, and more diverse groups of participants. It will also be important to determine the optimal training methods and performance criteria for stress-detection dogs.
Nevertheless, this study provides an exciting proof-of-concept for a novel way that dogs may be able to support the wellbeing of people with PTSD. It also underscores the incredible sensitivity and trainability of dogs’ noses, and their immense capacity to help us navigate the challenges of being human. As we continue to unravel the mysteries of the human-canine bond, it’s clear that our furry companions still have much to teach us – and much comfort and aid to offer.