For example, diabetic ketoacidosis can cause fruity or acetone-smelling breath. However, with their powerful noses, dogs can detect many odors that humans are simply unaware of. For example, diabetic alert dogs can tell when their owner’s blood glucose levels are off because of changes in volatile organic compounds in their owner’s exhaled breath. And dogs have been shown to detect various types of cancer simply by sniffing samples of a patient’s tissue or even just their breath or urine.
So, if illness changes your body chemistry and your dog knows how you’re supposed to smell, it shouldn’t come as a surprise when they react to your illness. Dogs also read human body language extremely well. Even free-ranging dogs can follow human pointing gestures. So, your dog is constantly watching you and interpreting your behavior. “Owners of therapy dogs often say that their dogs seem to know the person in the room who needs them most,” Dr. Burch says. “When a dog gets close to someone who is sick or depressed, the dog could be sensing a decrease in hormones such as oxytocin, dopamine, and serotonin. Studies have shown that petting a dog can reduce a person’s blood pressure, and the dog may sense it can make a person feel better.”