A new study has found that dogs can identify acute psychological stress with an accuracy of 93.75% which is analogous to physical changes in human breath and sweat.

Odors, such as body odor, are chemical signals that exist for communication between species, but now they have been found to have a more significant role in human-animal interactions. Dog’s sense of smell is remarkably strong and they are domesticated animals with close history with humans. Researchers wonder if dogs are smelling odors in the air and sensing the anxiety or stress of the owner, before responding to it.

The researchers collected a couple of samples from people after they completed an intense task. They collected the samples before and after the task, as well as from those who were showing signs of stress. Samples were tested on dogs that had been trained to sniff out the difference between stressed and relaxed humans. These dogs were presented with both the stressed and relaxed smell samples, but only responded to the one that was stressed.

Dogs are excellent at identifying the stress hormone, cortisol. When dogs were treated with samples of cortisol, they performed their alert behavior in nearly every trial. Dogs can also identify cortisol in samples of stressed and relaxed individuals.

Dogs are able to detect the change in VOCs, or chemical compounds that release as responses to stress. This tells us more about the human-dog relationship and could have implications for service dogs who are currently trained by visual cues.