How the smell of stress affects the emotional state of dogs: new research reveals an association between human stress and the dog's reaction

Recent research shows that the scent of a stressed person can subconsciously influence the emotions and decisions of people nearby. A team of researchers from the Faculty of Veterinary Medicine in Bristol wanted to find out if dogs experience changes in learning and emotional state in response to the scents of human stress or relaxation.

The team used an 'optimism' or 'pessimism' test in animals, based on findings that 'optimistic' or 'pessimistic' choices in humans indicate positive or negative emotions. The study involved dog owners and their pets, a total of 18 pairs, who went through a series of experiments with different human scents.

During the experiments, the dogs were trained to recognize when a food bowl at one location contained a treat, and when at another location it contained nothing. Once the dog learned the difference between these bowl locations, it would approach the location with the treat faster than the empty location. Researchers then tested how quickly the dog would approach new, ambiguous bowl locations placed between the original two.

A fast approach indicated 'optimism' about the presence of food at these ambiguous locations – a sign of a positive emotional state – while a slow approach indicated 'pessimism' and negative emotions. These experiments were repeated while each dog was exposed either to no scent or to the scents of sweat and breath from people in a stressed (arithmetic test) or relaxed (listening to soundscapes) state.

Researchers found that the scent of stress slowed the dogs' approach to the ambiguous bowl location nearest to the trained empty bowl location. This effect was not seen with the scent of relaxation. These findings suggest that the scent of stress might have increased the dogs' expectations that the new location did not contain food, similar to the nearby empty bowl.

The connection between human stress and dog reaction
Researchers suggest that this 'pessimistic' response reflects a negative emotional state and that it might be a way for the dog to conserve energy and avoid disappointment. The team also found that the dogs continued to improve their learning about the presence or absence of food at the two trained bowl locations and improved faster when the scent of stress was present.

Dr. Nicola Rooney, senior lecturer at the Faculty of Wildlife and Conservation at the Faculty of Veterinary Medicine in Bristol and lead author of the study, explained: “Understanding how human stress affects dog welfare is an important factor for dogs in shelters and when training companion and working dogs, such as assistance dogs.

Dog owners know how sensitive their pets are to their emotions, but here we show that even the scent of a stressed, unknown person affects the dog's emotional state, perception of rewards, and learning ability. Working dog handlers often describe how stress is transmitted through the leash, but we also showed that it can be transmitted through the air.”

Dr. Zoe Parr-Cortes, a doctoral student at the Faculty of Veterinary Medicine in Bristol and the principal investigator of the project, expressed gratitude to everyone who participated in the study, especially all the participants and dog owners who took part in the research.

Further research found that dogs reacted to the scents of unknown people similarly to the scents of their owners. This means that dogs can recognize and respond to emotional changes in people with whom they do not have a close bond. This ability can be crucial for understanding how dogs communicate and cooperate with people in various situations, such as working roles or therapy programs.

It was also noted that dogs use their sense of smell to assess people's emotional states, which helps them adjust their behavior according to the emotional context. For example, a dog may become more cautious or less inclined to interact if it senses stress in an unknown person. This finding further emphasizes the importance of understanding and managing one's stress when in the company of dogs, whether they are our pets or dogs in working roles.

Source: University of Bristol