For some time now, scientists have used dogs to sniff out a variety of illnesses, from Parkinson’s to cancer and, most commonly, diabetes. Though it is still a bit of a mystery, recent studies have started to give us insight into just how dogs are able to detect even the slightest scent. And for a disease with a symptom that may take away a person’s ability to smell, it feels a bit like poetic justice that dogs may be able to identify the coronavirus by smell.

Dogs’ noses have around 300 million scent receptors, making them superior smellers to humans who only have about 5 or 6 million. This amount of scent receptors allows dogs to create a mental view of the world around them. While their eyesight is poor in comparison to human eyesight, their noses more than make up for this.

According to Senior Research Fellow and head of the Dog Cognition Lab at Barnard College Alexandra Horowitz, a dog can even detect a teaspoon of sugar diluted in a million gallons of water (the equivalent of two Olympic sized pools).

With the influx of COVID-19 cases, it makes sense that researchers would want to find a way to apply this science to detecting positive samples of the virus. One of the first studies took sweat samples from 177 possible COVID-19 patients in five different hospitals in Paris and Beirut. They then used these sweat samples to train 14 dogs, six of which were further tested in the study.

These five Belgian Malinois and one Jack Russell terrier that were chosen were then asked to detect a positive SARS-CoV-2 sample from a lineup of three or four cones that contained negative samples. The dogs did dozens of trials, with a success rate of between 76% to 100%. Two dogs that had previously specialized in detecting colon cancer, had a 100% success rate of the 68 tests they completed.

The dogs may even be able to detect false negative tests. During the testing, two samples collected from individuals who tested negative were repeatedly marked by the dogs. The relevant hospitals were informed, and in subsequent tests these individuals tested positive.