How strong is a dog’s sense of smell? Even stronger than you might think. Your dog’s nose can detect substances that are concentrated to one part per trillion — that’s the equivalent of one drop of water in 20 swimming pools. Humans have around six million smell receptors, dogs can have up to 300 million.

This olfactory power has made dogs a valuable resource for the military, law enforcement, and even the medical community. Dogs around the world aid doctors and patients by sniffing diseases and incoming medical emergencies like diabetic shock. It’s still unclear whether COVID-19 has a unique odor, but researchers in Pennsylvania are hopeful that dogs can provide an answer.

How Do Dogs Sniff Out Diseases?

The science behind medical alert dogs and other life-saving canines is still a bit of a mystery. Medical experts have evidence that dogs can identify diabetes, Parkinson’s, and several forms of cancer, but they’re not sure what exactly it is that dogs are smelling. Whatever these substances are, experts call them volatile organic compounds (VOCs).

Dogs learn to detect diseases much the same way they learn to detect narcotics or bombs. They are presented with scents and rewarded for identifying or selecting the appropriate one. With time, they learn to associate this specific scent with a reward and identify it at the exclusion of others.

In a medical setting, test samples may include urine, blood, or saliva from an affected patient. Recent studies suggest that dogs may even be able to identify signs of bacterial infection by sniffing these samples.

Can Dogs Smell COVID-19?

A shocking number of people contract COVID-19 and never find out about it. In many cases, this is because their symptoms are mild, irregular, or non-existent. Global health organizations have warned, however, that asymptomatic carriers can still spread the virus and could in fact present an especially grave public health risk.

That’s one of the reasons researchers at the University of Pennsylvania’s School of Veterinary Medicine (PennVet) are working with a team of dogs to determine if COVID-19 has a detectable scent. The study, which began in late April, “sets the stage for dogs to be a force multiplier in the mission to detect COVID-19.” PennVet is working with eight dogs and using both urine and saliva samples throughout its tests.

In addition to sniffing out asymptomatic carriers, researchers believe that dogs could play an important role in settings where administering traditional tests is impractical or impossible. Offices and hospitals, for example, might introduce COVID-sniffing dogs to make testing and distancing measures more effective.

This work could prove especially crucial as America continues to reopen. As PennVet’s Dean Andrew W. Hoffman puts it, “What we do now, and how we do it, is relevant now more than ever before.” His words ring even more true nearly two months later.