Study Proves That Dogs Can Detect Stress Levels in Humans

Not only can dogs smell the odor of stress, but it's been found to affect their behavior.

Most dog owners could probably tell you, at least anecdotally, that their furry friends have the ability to pick up on their moods, and will even try to comfort them. So it may come as little surprise that a new study has found dogs can indeed recognize the smell of human stress and will adapt their behavior accordingly.

The study, which was conducted in a joint partnership with the University of Bristol, Cardiff University and the British charity Medical Detection Dogs, was published Monday in the journal Scientific Reports. In coming up with their findings, researchers tested 18 dogs with food bowls under a variety of conditions using odor samples from volunteers who were unfamiliar to the dogs.

In the initial test, dogs were introduced into a room that had food bowls in opposite corners—one that contained a treat and the other empty. Eventually, the dogs learned which bowls contained food and would proceed directly to those bowls.

Meanwhile, the researchers put the volunteers through stress tests by asking them to prepare and deliver an impromptu, five-minute speech followed by solving a complex math problem. In the second scenario, the volunteers were then presented with a comparatively relaxing activity that involved lounging on a beanbag chair in dim lighting while watching a 20-minute video of forest and seaside scenes on a laptop with headphones.

The researchers measured stress indicators, including cortisol levels and heart rate, during both of activities, and collected saliva and sweat samples using pieces of cloth placed under the volunteers armpits.

The dogs were then introduced to a single bowl placed in the room that contained food, in what was referred to as an "ambiguous scenario," and provided with the volunteer odor samples in several scenarios in different orders with the bowl in multiple locations. While the relaxed smells did not have any measurable effect on the dogs, researchers found that the animals were more hesitant to approach a bowl when it was associated with the stress of a stranger.

Dr. Zoe Parr-Cortes, Ph.D. student at Bristol Veterinary School and lead author on the study, noted that the research was the first to correlate how the detection of differences in odor can impact a dog's 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," explained Parr-Cortes, via NPR. "They might be less likely to try something risky if they think they’re going to be disappointed.”

“Importantly, it highlights how in-tune dogs are at picking up on mood," Parr-Cortes added. "So keeping your relationship with your dog \… based on positive reinforcement and happy, fun engagement is the best way to have a good relationship and a happy dog."

So while the companionship of dogs can provide a myriad of health benefits, such as an overall longer life and decreased risk of dementia, if nothing else the study is a good reminder that dogs likewise rely on their humans for their own peace of mind.