A dog’s snoot may be well-suited to sniffing out stress in humans, new research out Wednesday suggests. The small study found that dogs could be trained to recognize the odors of stressed people and to distinguish these signals from those collected during non-stressful times. The findings only further highlight the unique relationship between humans and canines, the researchers say, and may even have implications for training service and other kinds of working dogs.
Scientists at the Queen’s University Belfast in Ireland recruited four dogs and 36 humans for the experiment. They collected samples of sweat and breath from the human volunteers under two different conditions: A “baseline” condition and a “stressed” condition, caused by the humans having to solve a hard math problem. To ensure the authenticity of the stressed odor samples, the researchers only used those collected when people’s blood pressure and heart rate had gone up.
For the second part of the study, the team introduced the dogs to the stressed samples, training them to communicate when they sniffed one out. Then they had the dogs exposed to a person’s baseline and stressed samples at the same time, along with a blank sample containing no human odor. Across all the guessing sessions, the dogs were highly accurate at telling apart a person’s stressed odors from the others, with a combined 93.5% accuracy rate for all four dogs. The findings are published in PLOS One.
Other studies have suggested that dogs can tell the difference between people’s varying emotional states, including stress. But according to study author Clara Wilson, these studies have largely relied on looking at how dogs respond to visual or auditory cues of stress, or in studying dogs’ biological responses to seeing human stress, such as changing levels of cortisol (cortisol being a important stress-related hormone in both dogs and humans). But their findings not only indicate that our odors can subtly shift when stressed but also that dogs can notice this shift.
“The take-home message of this study is that our bodies’ psychological stress response changes the smell of our breath and sweat, and that dogs can detect this change,” Wilson, a PhD student in the School of Psychology at Queen’s, told Gizmodo in an email.
Many dog owners will swear that their dogs are highly attuned to their emotions and that they will often respond accordingly to provide comfort in times of stress. These findings don’t directly show that dogs can comprehend the meaning of a person’s emotionally charged body odor, Wilson points out. But there is other evidence suggesting that dogs will regularly mirror the emotions of their humans, a form of basic empathy known as emotional contagion. And if that’s true, then our body funk could play a role in why dogs can read us so well.
“While our study does not allow insight into their conceptual understanding of this odor, it adds supporting evidence that odor may have been a contributing factor in relation to the previous study findings assessing emotional contagion between dogs and humans,” Wilson said.
Wilson also argues that these findings could have practical applications for how we train service dogs and other dogs that have to work closely with humans.
“Knowing that there is a detectable odor component to stress may raise discussion into the value of olfactory-based training (e.g., taking samples from a person when relaxed and experiencing stress) and positively reinforcing the dog to attend or perform attention-seeking behaviors in response to this odor,” she said. But any such training methods need to be tested out in real-world settings before they became accepted practice, she added.
Many of the team’s researchers have since moved onto other universities, so a direct follow-up to this study is unlikely any time soon. But Wilson will continue researching how dogs—including working dogs—smell the world around them, so she does hope to someday return to the topic. And she says that there’s plenty left for future studies to explore.
“While training ‘sniffer dogs’ on human biological samples in a laboratory has previously mostly been in relation to diseases and health conditions, it is exciting to see that this paradigm can be adapted to also let dogs communicate directly with us as to whether they can smell other parts of the human experience, such as psychological processes,” she said.