Researchers Say Your Canine Companion Can Smell Your Stress Levels

Humans have a wide range of nuanced emotions, but a new study published in PLOS One indicates that dogs may be able to pick up on one of our emotions in particular — stress. Researchers from Queen's University in the U.K. set out to determine if canines could differentiate between human baseline emotions and states of stress using only their sense of smell, reports NBC News.

As per the research, stress can elicit a host of changes in the human body including the release of cortisol, elevated heart rate, blood pressure, reduced digestion, and chemical changes in both sweat and breath particles. Four dogs were issued sweat and breath samples from 36 participants over the course of 36 sessions. 

In the first phase of the study, the dogs were presented with two blank samples, as well as a stress sample taken after participants had undergone a challenging math task. As reported via NBC News, the task involved continuously counting down out loud by 17 starting at 9,000 with a time limit of three minutes. In the second part of the study, the dogs put their nose to a blank sample, a stress sample, and a sample taken before starting the math task to represent participants' baseline emotional state.

Are dogs affected by our stress levels?

The study team measured participants' heart rate and blood pressure prior to beginning the task, as well as after, reports NBC News. They also gathered questionnaire data pertaining to participants' self-reported states of stress. Trained to indicate the stress sample, the canines did so successfully with an accuracy rating spanning 90% to nearly 97%, as written in the study. "This study provides further evidence of the extraordinary capabilities of 'man's best friend,'" animal psychologist and first author on the study Clara Wilson states via NBC News.

Yet little is still known as to whether or not our furry friends feel our stress in return. However, Healthline cites a 2019 study published in Scientific Reports that suggests they may. Along with gathering questionnaire data pertaining to the personality traits of dogs and their owners, researchers also examined hair samples from both the human and their dog to assess cortisol concentrations, otherwise known as the stress hormone. Although the samples were taken during two different seasons of the year, the hairs revealed cortisol levels of owners and their dogs to be in sync.