Dogs Can Smell Our Stress—And It's Contagious

Dogs have a fantastic sense of smell: A canine’s nose is 10,000 to 100,000 times stronger than a human's. Now, new research shows that when they sense people's stress levels with their snouts they react accordingly. 

A recent study published in the journal Scientific Reports found that dogs are more likely to act pessimistically after sniffing an anxious person’s sweat. For their research, a team of scientists in the UK asked 11 volunteers to speak publicly and perform math problems in front of others to generate anxiety. In another session, the same participants watched 20-minute videos of relaxing scenery in a calm place.

The experimenters tracked each participant’s heart rate. They also collected breath, saliva, and sweat samples to measure cortisol—a hormone associated with stress that shows up in bodily fluids. All volunteers took anxiety questionnaires before and after the study.

Meanwhile, 18 dogs were trained to learn that food was always in a bowl in a specific spot. The pets also realized a bowl in another section of the room never contained food.  The researchers then observed how the canines approached new bowls placed between the previous two. The goal was to see if the animals seemed optimistic or pessimistic about the possibility of food in an ambiguous bowl.

After smelling sweaty clothing from the anxious volunteers on several separate occasions, the dogs were more likely to slowly approach a new bowl when placed closer to the empty bowl. That implies the dogs believed there would be no treat in the bowl and would approach it pessimistically. The dogs’ attitudes didn’t seem to change after they smelled the sweat of relaxed people. 

The odor of stressed-out sweat may have a bigger influence on a dog’s appetite than their decision-making abilities. Stress reduces hunger, so the scent of an anxious, sweaty human may make dogs feel so on edge that their appetites shrink. Nonetheless, the research shows that a stressed owner can negatively impact dogs.

The fact that dogs can be hypersensitive to their owners’ stress levels has been demonstrated before. A 2019 study investigating the phenomenon asked participants questions about their personality traits, including neuroticism and openness. They were also instructed to complete personality questionnaires for their pets covering factors like excitability, fearfulness, and aggression.

The researchers then analyzed the hair cortisol concentrations in 58 dogs and their owners. The researchers found that the cortisol levels of the canines were in sync with those of their owners. This implies that dogs are highly empathetic and have similar emotional responses to people. 

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