Many people have dogs as pets because it’s a well-known fact that they help relieve stress. Nothing compares to the feeling of coming home to a loving, furry friend after a hectic workday. As emotional creatures, dogs can understand subtle changes in how humans feel. They’re insanely attuned to humans since domestication allowed them to connect with people on a much deeper level. According to a new study from Queen’s University Belfast, they can detect human stress hormones using their noses.

The study, which appeared in the journal PLOS ONE, discovered that dogs use their sense of smell to differentiate between a relaxed and stressed human. The study included four dogs from Belfast — Fingal, Soot, Treo, and Winnie — along with 36 people.

How Researchers Tracked Dog Responses to the Human Stress Hormone

Researchers collected sweat and breath samples from volunteers before and after they did a math problem. They took the samples just four minutes apart during an exercise where people had to count backward from 9,000 in increments of 17.

If the participant responded correctly, the researchers didn’t give feedback and expected them to continue. The team only interjected when a participant gave an incorrect answer, in which case they provided it.

Participants self-reported their stress levels on a questionnaire before and after the activity. However, the scientists only used samples from people with elevated blood pressure and heart rate. Then, they trained the dogs to ensure they could distinguish between a “stress” sample and a “baseline” sample.

Next, the researchers presented the samples to the dogs, some of which came from people who had just finished math problems. The other samples came from the same participants before they attempted the equations.

To test the dogs’ accuracy, the team placed three items in a container: a new piece of gauze, a sample from a stressed person, and one from the same person when relaxed.

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Study Shows Dogs Use Their Noses To Identify Stress

Incredibly, the dogs accurately identified the stressed sample in 675 out of 720 trials, or roughly 94%.

Clara Wilson, a Ph.D. student in the School of Psychology at Queen’s, explained: “The findings show that we, as humans, produce different smells through our sweat and breath when we are stressed and dogs can tell this apart from our smell when relaxed — even if it is someone they do not know.”

The team said that dogs could sense physiological changes in our sweat and breath triggered by stress hormones. One of the main chemicals that dogs can sniff out is volatile organic compounds (VOCs). We emit these compounds daily through breath, sweat, skin, urine, and feces. Having a healthy amount of VOCs in the body keeps it functioning well.

However, a high VOC level can indicate heightened stress and anxiety, and dogs often detect these changes. Excess VOCs cause the body odor to change, and since dogs primarily use the sense of smell, they pick up on it quickly. Researchers said that even untrained pet dogs might notice odor changes when a human feels stressed.

The findings don’t reveal whether the dogs perceived the stress samples as indicative of a negative emotional state. In most settings, dogs probably utilize other senses and environmental cues to assess a situation. For instance, they might read the emotions on their owners’ faces or listen to their voices. The study does prove that dogs can detect a stress odor in the given samples, though.

Since dogs can identify an odor linked to human stress, it proves the importance of our relationships with canines. The researchers believe the findings could lead to future scent-based training for PTSD or psychiatric service dogs.

People With Service Dogs May Benefit From the Findings

Psychiatric service dogs assist their owners in performing everyday tasks that otherwise might be too challenging. In addition to providing emotional and mental support, service dogs can:

  • reduce anxiety through tactile stimulation
  • nudge/paw at their owner to bring them back to the present
  • interrupt undesirable behaviors
  • provide constant body contact and deep pressure stimulation
  • block contact with others
  • bring medication
  • assist with balance
  • fetch a phone or device

While medical alert service dogs undergo scent training, only some service dogs receive this training. The findings will likely lead to a larger pool of service dogs able to sniff out stress in humans.

Researchers added that they couldn’t determine whether the dogs in the study felt empathetic toward stressed humans. Wilson said they trained the dogs using positive reinforcement to locate their target. So, they showed excitement upon finding the stressed hormone sample rather than feeling tense.

Nonetheless, the fact that dogs can detect subtle physiological changes in hormones means they can respond accordingly after training. After all, they don’t necessarily need to understand the emotion to react to it.

And since dogs have so many smell receptors, they can detect odors that humans might miss. This innate ability makes them able to respond quickly, proving useful in life-threatening situations.

“The research highlights that dogs do not need visual or audio cues to pick up on human stress. This is the first study of its kind and it provides evidence that dogs can smell stress from breath and sweat alone, which could be useful when training service dogs and therapy dogs,” Wilson added.

“It also helps to shed more light on the human-dog relationship and adds to our understanding of how dogs may interpret and interact with human psychological states.”

Treo, a two-year-old Cocker Spaniel, was one of the super sniffer dogs involved in the study. His owner Helen Parks said: “The study made us more aware of a dog’s ability to use their nose to “see” the world. We believe this study really developed Treo’s ability to sense a change in emotion at home. The study reinforced for us that dogs are highly sensitive and intuitive animals and there is immense value in using what they do best — sniffing!”

stress hormones

Final Thoughts on Dogs Detecting Stress Hormones Through Sense of Smell

A new study shows that dogs can identify stress using their noses to detect subtle hormone changes. For instance, humans have a higher level of VOCs in their breath and sweat when stressed. Dogs can easily smell these differences and help their owners relax by cuddling or pawing at them. Researchers hope the findings will lead to future scent-based training for psychiatric service dogs.