When you’re stressed, does your dog’s behavior change? Perhaps your dog watches you more closely or makes an extra effort to comfort you with cuddles. It may even look as if your dog knows how you’re feeling. But what could your dog be sensing? And perhaps more importantly, what impact does your stress level have on them?
Do Dogs Know When You’re Stressed?
According to Dr. Zoe Parr-Cortes, veterinarian and PhD graduate from the University of Bristol, research studies support the idea that dogs can sense stress in people. “As one of our closest companions, dogs have co-evolved alongside humans for thousands of years. Because of this, both humans and dogs have learned to recognize cues in each other that signal how the other is feeling. Several studies have demonstrated that dogs respond to the sights and sounds of various human emotions, including crying, vocal tones, and facial expressions.”
For example, scientists have shown that your dog can hear your mood in the tone of your voice. The sounds of happiness are likely to result in a positive reaction, like tail wagging, whereas sadness and fear can result in a negative reaction, like yawning. And research in the journal Biology Letters showed that dogs have the ability to match your mood to the look on your face. So if dogs know when you’re happy or sad, it makes sense that they can sense your stress, too.
How Do Dogs Sense Your Stress?
Dr. Parr-Cortes says dogs can sense stress based on a combination of cues and the context of the situation. They can observe your facial expressions and body language and listen to the tone of your voice. And of course, dogs have powerful noses that can detect changes in how we smell. “When we’re stressed, we act and communicate differently, and our dogs will notice this. However, while sight and sound may be more obvious for us to recognize as cues, smell is a sense that is much more important to dogs than humans,” she explains.
Research published in PLOS One showed that dogs can detect stress from sweat and breath samples alone. For the study, human participants provided baseline sweat and breath samples. Then, the researchers administered a math test to the participants, with the intention of causing them stress, before collecting a second set of samples. When researchers presented the samples to dogs, they could tell the difference between the baseline and stress samples with over 90% accuracy. It seems that acute stress changes what’s known as volatile organic compounds in breath and sweat. These compounds are detectable to dogs’ noses.
How Do Dogs Smell Stress?
So what exactly are the dogs smelling? That’s harder to pin down. In a recent study published in Scientific Reports, Dr. Parr-Cortes and other members of the Animal Welfare and Behaviour Group at Bristol Vet School stressed human participants with public speaking and an arithmetic test. To measure stress, the research group and its principal investigators, Dr. Nicola Rooney and Professor Mike Mendl, looked at the participants’ cortisol (a hormone released by the adrenal gland during times of stress), heart rate, and the participants’ own rating of anxiety levels. And of course, they collected sweat samples.
For the study, Dr. Parr-Cortes and her colleagues primarily selected samples from people with the highest cortisol response. They thought this would be a good marker to use because the charity Medical Detection Dogs has trained dogs to smell when the cortisol levels in people with Addison’s disease drop too low. And based on the current study’s findings, it seems that even untrained dogs may be able to detect differences in cortisol via scent.
But cortisol may not be the whole story. Dr. Parr-Cortes says, “Interestingly, we found that some people self-reported high anxiety levels, but their cortisol did not increase much, and others had the opposite response. Therefore, it would be interesting to know what exactly dogs are responding to. Is it cortisol, adrenaline, or another stress marker? What’s interesting about this study is that the odors came from unfamiliar people, suggesting a common ‘stress’ smell among individuals that dogs can identify without prior training.”
To identify that potential stress smell, Dr. Parr-Cortes and members of Bristol Vet School are currently working on measuring the odor differences in the samples using volatile organic compound analysis. However, it’s possible dogs can detect subtle differences or patterns in odor that chemical analysis can’t.
Does Your Stress Impact Your Dog?
But why would this ability to notice human stress have evolved in dogs? Because they live in social groups. Dr. Parr-Cortes explains that detecting stress in another group member is beneficial to any group-living organism as it aids survival. If something is threatening to the other member, it can also be a threat to you. This ability to sense alarm in others is known as fear contagion.
Although it aids survival, does your stress impact your dog’s well-being? Dr. Parr-Cortes’ study would indicate yes. It influences their emotions and the decisions they make. “We found that when the stress odor was present, dogs were less likely, and slower, to approach a bowl that they were uncertain contained a treat. This suggests that being stressed around your dog, or even just being around the smell of another person who is stressed, may have a negative effect on your dog’s mood and possibly even your relationship with your dog.”
Therefore, it’s important to appreciate the repercussions of human stress on a dog’s wellbeing, as well as on their learning and performance. “Maintaining a relationship based on positive reinforcement and engaging activities is the best way to keep your dog happy,” Dr. Parr-Cortes advises. Learn to spot your dog’s stress signals, keep calm around your dog, and consider doing a relaxing activity before interacting or training to reduce any effect your stress might have.