Researchers at the University of Naples have found that dogs are sensitive to a person’s change in mood, tone of voice, and body smells that can occur with the onset of disease or an emotional breakdown.

According to science, dogs can tell when their humans are having a rough time, and they use a wide variety of signals to figure it out. Not only can your pet tell when you have a virus or serious diseases like certain types of cancer, but domestic dogs have also shown an aptitude for accurately detecting mood fluctuations.

Alexandra Horowitz, the head of the Dog Cognition Lab at Barnard College explains that if a person is infected with a virus or bacteria, they smell different. Some illnesses like Parkinson’s disease, typhoid, or yellow fever are known to change a person’s body odor so profoundly that even other people can notice. 

Dogs are able to smell changes in their owners that would escape human senses, or that occur so early on that the sick person barely feels any different. Medical detection dogs are trained to smell early cancer signs with over 95% accuracy, and several teams are currently training dogs to detect COVID-19 in humans.

Dogs have demonstrated to be able to detect early signs of ovarian and pancreatic cancer that doctors describe as “hidden", and alert their owners. Some forms of cancer do not produce detectable symptoms until later stages of the disease, and can slip past blood tests unnoticed. By the time the disease is caught at those late stages, therapy isn’t effective and the odds of survival are slim.

Researchers have also found that a person’s mood or tone of voice—which can be an indicator of a serious illness or mental breakdown—also triggers a dog’s sense of protection and ability to alert. Human emotions manifest physically in chemosignals that are emitted by the body, and dogs can detect those minute changes through smell.