Yes, dogs can smell your stress

As any dog owner will attest, dogs can seem eerily attuned to human behavior. When humans yell or pick a fight, dogs often respond with anger and fear. Similarly, people with a sedentary lifestyle may have seemingly sedentary pets: a 2021 study found a correlation between dog obesity and human obesity.

This article first appeared in Salon.

Now, a new study sheds light on the peculiar ways that dogs seem to be able to pick up on human vibes. Specifically, researchers found that when you are stressed, your body produces a distinct odor — and our canine friends can smell it.

This likely is not a surprise for dog owners. Scientists have already demonstrated that dogs feel love for their owners, lead rich interior lives and can even cry tears of joy. Yet even though scientists know that dogs feel complex emotions, the research is still murky on whether they can literally smell a person's emotions. A research team including scientists from Queen's University Belfast and Newcastle University set out to shed light on the subject.

"While we as humans are very visual, this finding reminds us that there may be things that dogs are able to pick up on that we aren't even consciously aware of."

"Dogs possess an incredible sense of smell, which enables them to detect diseases and health conditions from odor alone," Dr. Clara Wilson from Queen's University Belfast told Salon by email. "Whether these capabilities extend to detecting odors associated with psychological states has been explored far less."

To test their hypothesis, the researchers found pet dogs who had no previous scent training so they could teach them scent discrimination using odors that had known differences with each other. After 16 of the dogs displayed indifference to the "scent games," the team narrowed their pool down to four individual dogs. Those dogs were then exposed to combined breath and sweat samples from humans — first when those people were in a relaxed state, and then when they were in a state of stress from doing difficult arithmetic problems. Each person acted as their own control.

The results spoke for themselves.

"From the very first time the dogs were exposed to the baseline and stress samples, they communicated that these samples smelled different," Wilson told Salon. "In 94% of 720 trials they correctly chose the stress sample."

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This study has significant implications, but there are limitations to its effectiveness. As Wilson noted, the study does not provide any indication as to whether the dogs connected the difference in the stress samples with actual negative emotional states; all it establishes is that they could detect the odor differences. In fact, while dogs are uniquely attuned to human stress, it is almost certain that they use a number of cues to ascertain their companions' emotional states.

The significance of the study, however, rests in how it underscores the deep connection between humans and dogs — as well as the different ways in which they process reality.

"Establishing that dogs can detect an odor associated with human stress provides deeper knowledge of the human-dog relationship and how they interact with the world around them," Wilson told Salon. "While we as humans are very visual, this finding reminds us that there may be things that dogs are able to pick up on that we aren't even consciously aware of, and I think that gives us a really great snippet of insight into how dogs' may be perceiving the world around them through their noses."

Salon also reached out to Dr. James A. Serpell, Professor of Ethics & Animal Welfare at the University of Pennsylvania School of Veterinary Medicine, who was not involved in the study. Serpell began by pointing out that because the study took place in a strictly controlled environment, it is unclear whether the results would hold when applied in the real world. At the same time, Serpell argued that the study has potential value.

"It might also argue for the use of dogs in airports, etc., to detect potential terrorists just on the basis of their odor—the so-called 'scent of fear.'"

"The findings tend to reinforce anecdotal evidence that some dogs are sensitive to people's moods and mental states, and might support the use of dogs therapeutically for people with conditions such as PTSD, etc.," Serpell wrote to Salon. "It might also argue for the use of dogs in airports, etc., to detect potential terrorists just on the basis of their odor—the so-called 'scent of fear.'"

More research will be needed to dig into these details — a fact that Wilson pointed out to Salon.

"As a within-subject design, we are confident that the odor change that the dogs detected was caused by the onset of stress," Wilson explained, adding that this means odor is obviously important to how humans and dogs interact, perhaps even more so than scientists previously believed. "We can move forward with future studies that may want to address this more naturalistic setting with confidence that odor is likely an important component that we might not have prioritized when considering this interaction beforehand."

In a previous interview with Salon about dogs, Dr. Catherine Reeve of Queen's University Belfast's School of Psychology (who also participated in the study) noted that dogs use their incredibly strong sense of smell to understand and communicate with each other.

"When sniffing one another, dogs are getting all the information they need about other dogs' sexual status, health status, age, etc.," Reeve told Salon.