We know that dogs can likely sense when humans are stressed. Now, researchers at The Queens University at Belfast have figured out at least one way how.
Stress, generally defined as a physiological and psychological response to challenging circumstances, drives anxiety, panic attacks, and PTSD. Anxiety worsens when the person experiencing stress doesn’t feel they can control the situation. When experienced as an adverse event, stress can evoke some of the same physical responses as fear.
Some physiological changes that occur in humans when stressed include increased heart rate, increased blood pressure, respiratory distress, and release of the hormones epinephrine and cortisol into the bloodstream. Whether or not someone experiences these physical changes, and to what degree, depends on whether stress is felt more negatively, as a threat, or in a more positive light, as a challenge.
Owners of trained medical alert dogs report that stress is the condition that most commonly causes the dogs to display alert. Studies have shown that dogs sense human feelings and emotions through sound and sight. Dogs also experience emotional contagion and “mirror” or reflect their owners’ state of mind. A dog’s blood levels of cortisol can even be similar to that of its owners.
A sense of smell is essential for dogs to understand their surrounding environment. Therefore, the British researchers tested the premise that dogs respond to changes in human physiology associated with a psychological state (such as negative stress) by detecting changes in the human body odor.
Previous studies established that humans release different levels of volatile organic compounds (VOCs) in their breath and skin when calm and experiencing stress. This study aimed to determine whether or not dogs can discriminate between different levels of VOCs.
They took breath and sweat samples from 30 participants—both dog owners and strangers—while feeling neutral and while they experienced a state of stress through an experimentally-induced psychological threat: solving a difficult math problem under pressure for timing and accuracy while being given no feedback.
The researchers used self-reported stress scales and measures of heart rate and blood pressure at baseline and during stressful events. This method ensured that human study participants—the dog owners and other strangers to the dogs—were experiencing negative stress when samples were collected.
The study dogs—a cocker spaniel, a cockapoo, and two with undetermined mixed-breed backgrounds—were trained to recognize and discriminate between the baseline and stress samples and to perform alert behavior when presented with stress samples.
Researchers kept dog handlers unaware of which sample was which, so they wouldn’t be able to influence the dog’s decisions.
Each dog participated in 20 discrimination trials, and their choices were consistently performed with high accuracy, above the level that could be considered chance. Statistically, the dogs’ overall performance was 93.75 percent correct choices and 94.44 percent of the time correctly choosing stress samples, almost always on first exposure to the sample. Testing also indicated that the dogs used only scent and not any other type of cues to discriminate among samples.
This study contributes to further understanding of dog-human relationships and confirms differences in human VOC levels while relaxed and experiencing stress. With training, dogs can detect these differences.
These results are important because they indicate that adding olfactory distinction exercises could be useful in the current training programs for medical and psychological service dogs that are most often based only on visual cues.