January 11, 2025, 2:50 pm | Read time: 4 minutes
Dogs love to get close to us with their wet noses–often accompanied by a slobbery kiss. But when they specifically sniff our breath, there’s more to it than just the smell of our last breakfast. Biologist and PETBOOK editor Saskia Schneider reveals the fascinating details.
When dogs get close to our faces, they usually have moist intentions like a slobbery kiss on the nose. Sometimes, however, the four-legged friends also specifically sniff our breath. Most dog owners then suspect that the dog might still smell the ham toast from breakfast. That can certainly be the case. But there are other reasons why dogs sniff our breath. The four-legged friends can determine our mood and even detect diseases.
Why Dogs Sniff Our Breath
When we assess someone, we usually do so based on visual criteria. Our dogs, on the other hand, are “nose animals.” Compared to humans, they have 60 times more olfactory receptors. Therefore, dogs communicate a lot through smells–for example, by emitting certain scents that signal to other dogs: “I am ready to mate” or “I am sick.”
Even in living with us humans, dogs rely entirely on their noses. They not only recognize us by smell–they can also detect the slightest changes in it.
Also interesting: Why dogs like to sniff our crotch
Dogs Can Smell if We Are Stressed
With their keen noses, dogs can detect not only drugs but also diseases like cancer, diabetes, and even COVID-19. In a 2022 study, researchers were able to prove for the first time that the four-legged friends can also recognize when a person is stressed–based on their breath (PETBOOK reported).
For this, scientists at Queen’s University in Belfast presented four dogs with samples of body fluids from people who were either stressed or relaxed. With an accuracy of over 93 percent, the dogs were able to distinguish the scents. This was true for both sweat samples and samples of exhaled air.1
This suggests that the chemical components of our sweat and breath change when we are stressed. Our dogs can clearly perceive this difference. 2
Dogs Can Sniff Out Post-Traumatic Stress Syndrome from Breath
A relatively new study from 2024 shows that dogs can even smell from a person’s breath whether they have experienced a traumatic stress event. However, these results should be viewed with caution, as the experiment involved only two dogs specifically trained to detect certain scents.
Researchers suspect that dogs can detect certain organic components in the breath of people who are under extreme stress, such as when a trauma is recalled. If this ability is confirmed by further studies, it could be specifically trained in assistance or therapy dogs.
Dogs Can Smell Cancer in Other Dogs
Why dogs like to smell our crotch
Dogs Can Even Smell Diabetes in Breath
In diseases like cancer or diabetes, dogs are usually trained on the scent components. This is mainly achieved by collecting sweat samples. A 2016 study at the University of Cambridge in the UK proved that dogs can also detect the disease in breath–at least type 1 diabetes. 3
They perceive a chemical compound called isoprene in the breath of patients when they are about to experience hypoglycemia. The level of isoprene is then twice as high, which is easy for our four-legged friends to detect.
Dogs Probably Smell Even More Information in Our Breath
Dogs can not only indicate stress or diseases in humans, but they also notice when we are mentally unwell. For decades, the four-legged friends have been used as so-called “Emotional Support Dogs.” They can demonstrably improve their owners’ well-being by comforting or calming them.
Until now, it was assumed that dogs perceive human mood swings primarily through their behavior or body language. However, it is quite conceivable that body odors also play a role. There is, however, little scientifically reliable data or research on this.
Studies would also need to clarify to what extent dogs correctly interpret the smells or their altered composition. Does my four-legged friend know that I am sick because I emit a certain smell? Do dogs perhaps even consciously sniff our breath to check our health status? This question remains unanswered. But imagine if you could ask your dog in the future whether you should stay home and book a doctor’s appointment.
About the author: Dr. Saskia Schneider is a biologist with a doctorate. In her studies at the Free University of Berlin, she focused primarily on zoology and animal behavior.