GabyResearchers from the University of Bristol have discovered that human stress can lead to a sudden drop in a dog’s mood. This study by the university team is the first to show that the scent of human stress affects dogs’ emotions and behavior. While this may not surprise people who live with dogs, the researchers found that the effect is much stronger than previously thought. “Owners know how sensitive their pets are to human emotions, but here we show that even the smell of stress from a stranger can impact a dog’s emotional state, its perception of rewards, and its ability to learn,” said Nicola Rooney, the senior author of the study.
Since dogs can recognize both verbal and nonverbal signals from humans, the researchers decided not to expose them directly to stressed people. Instead, the dogs were given samples of sweat and breath collected from three unfamiliar volunteers while the volunteers were either relaxing or engaged in stressful tasks. The relaxing task involved watching a nature video, while the stressful task included irritating instructions related to math and public speaking.
What the Researchers Discovered
The team involved 18 pairs of dogs and humans in the scent-sample trials. During training, the dogs learned that a food bowl in one location always contained a treat, while a bowl in another location was always empty. Dogs that learned this pattern approached the bowl more quickly when it was placed in the positive location P (associated with treats) than when it was in the negative location N (associated with no treats). The scientists said the dogs’ active running between the bowls indicated optimism.
In the next phase, the researchers placed the bowls in three new locations to confuse the dogs. They repeated the treat experiment while allowing the dogs to sniff jars containing sweat from people in either a stressed or relaxed state. The dogs approached the bowl in the new location hesitantly and with uncertainty when they detected the scent of a stressed stranger, sometimes ignoring the bowl altogether. But when exposed to the scent of a relaxed person, they eagerly searched for treats in the unfamiliar spots, as reported by ScienceAlert.
“Dog trainers often say that stress is transmitted through the leash, but we have shown that it can also be transmitted through the air,” Rooney said.
The researchers classified the dogs’ reactions to human stress scent as pessimism. This negative emotional state may be adaptive, helping dogs conserve energy or avoid frustration. Much about this dynamic remains unclear. Further research is needed to clarify how human scents influence dogs’ emotions and learning.
“Understanding how human stress affects dogs’ well-being matters for animals in shelters and for training companion dogs,” Rooney said. The findings of the study were published in the journal Scientific Reports.
