Dogs Can Smell Shifts in Human Stress Levels and Adjust Their Behaviors in Response, Study Finds

07/24/2024 03:06 PM

"It kind of makes sense that dogs would learn to read our emotions... it might be helpful to them to know if there's something threatening," a researcher said

Dogs can smell whether a human is stressed or relaxed and will make behavioral decisions based on that information, according to a new U.K. study.

The study published in the journal Scientific Reports on Monday, July 22, tested a group of eighteen dogs to see how they would respond to the smell of people who were both stressed and relaxed. 

"Some people have looked at can dogs actually detect differences in odor. And they have. But nobody had really looked at how that affects the dog's emotions," Dr. Zoe Parr-Cortes, the study's lead author, told NPR.

The researchers determined that the dogs were "significantly less likely" to approach a food bowl if they smelled a stressed-out human than if they didn't, indicating "possible risk-reduction behaviors in response to the smell of human stress," according to the study. 

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The researchers initially tested the dogs' responses by placing bowls in one corner of the room that often contained food and empty bowls in the opposite corner of the room. The dogs learned to head toward the side where they knew the food was more likely to be.

In another part of the experiment, some human participants were put through stressful activities, including delivering an impromptu speech and calculating complex math problems. In contrast, others were left to rest in a comfortable chair with blankets and instructed to watch calming videos. 

During the tests, the participants' cortisol levels, heart rate, and self-reported anxiety were recorded. Researchers also collected samples of the participants' breath and sweat on rags.

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The rags were then released to the dogs. Dogs who smelled rags collected from humans involved in stressful actions were more hesitant to approach the food bowls. Canines who sniffed rags from humans participating in relaxing activities weren't as affected.  

"It basically shows that the stress smell might affect how [dogs] respond to ambiguous situations," Parr-Cortes told NPR. "They might be less likely to try something risky if they think they're going to be disappointed."

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Parr-Cortes said that this response was likely the dogs' reaction to instinct. The dogs' actions show that pet canines are "in tune" with humans' emotions.  

"Being a species that we've lived and co-evolved with for thousands of years, it kind of makes sense that dogs would learn to read our emotions because it might be helpful to them to know if there's something threatening in the environment or some stressor that they need to be aware of," she added.

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