7 Surprising Things Dogs Can Detect Through Their Sense of Smell

Dogs possess an incredible sense of smell, which is at least 10,000 times more sensitive than ours. While humans have 6 million olfactory receptors, dogs have up to 300 million. It's no surprise that they are being trained to identify a wide variety of things by scent, from explosives to viruses to fertile livestock. These remarkable animals are not only our companions but also exceptional scent trackers. Here are seven unusual things they've been trained to detect.

1. The Novel Coronavirus

Viruses have distinct smells, and scientists have found that dogs can recognize them. For instance, dogs have successfully differentiated between three types of bovine viruses—those responsible for diarrhea, herpes, and influenza. Now, dogs are being trained to detect human viruses. Cindy Otto, director of the University of Pennsylvania's Working Dog Center, is training eight Labrador retrievers to detect SARS-CoV-2, the virus behind COVID-19. If the pilot program succeeds, canine teams could one day help screen travelers at airports, patients in hospitals, or attendees at conferences.

Dogs that have been trained to detect malaria are now facing a similar challenge at the London School of Hygiene & Tropical Medicine. Researchers have gathered viral samples to train the dogs, and if successful, the UK government plans to deploy six of them to screen international travelers at airports.

2. Bronze-Age Human Remains

Cadaver dogs, also known as human-detection dogs, have the ability to identify the scent of decomposing remains in cold cases spanning decades. But can their keen noses trace odors that have been lingering for thousands of years? In 2015, Croatian archaeologist Vedrana Glavaš and dog trainer Andrea Pintar tested the dogs on Croatia's Velebit mountain range, where Glavaš had discovered parts of a 3000-year-old hill fort and burial site. Their 2018 study in the Journal of Archaeological Method and Theory showed that the dogs successfully located graves containing burial chests and human bones. The study suggests the dogs are detecting the molecules of human decomposition, and Glavaš believes the area's rocky, porous karst landscape preserves these molecules better than regular soil.

3. Fertile Cows

Determining when a cow is fertile, or in estrus, is crucial for dairy farmers to time artificial insemination effectively. In the past, farmers relied on behavioral cues like mounting. However, dogs trained to detect specific estrus-related scents may provide a more reliable method. Dogs can detect these odors in vaginal fluid, milk, urine, or blood samples with over 80% accuracy overall, and up to 99% accuracy in milk. A 2013 study found that 13 dogs, eight of which had previous training in detecting narcotics or cancer, were able to identify estrus-specific scents in cow saliva, successfully pinpointing estrus in nearly 60% of the samples.

4. People Carrying Explosives

Although invisible to the human eye, we all leave behind thermal 'plumes' as we move through the air—and dogs have been trained to detect these plumes for traces of explosives. At Auburn University's Canine Performance Sciences program, Labrador retrievers have been trained to identify body-worn explosives in crowded areas, such as large concerts and airports, by following scent particles in human heat plumes. This patented technique, known as Vapor Wake, is used to train dogs for law enforcement and mass transit security purposes.

5. Invasive Pythons

Auburn University’s detection dogs have been trained to sniff out Burmese pythons in Florida's Everglades National Park. These invasive pythons, which hide in the tall grasses of the Everglades, prey on native mammals and birds. In 2010, two dogs named Ivy and Jake located 19 pythons, and in 2017, Floyd and Vito found five pythons on North Key Largo in the Florida Keys. These python-sniffing dogs were trained as part of Auburn’s Eco Dogs program.

6. Bed Bugs

When bed bugs invade homes, they hide in cracks and crevices, making them hard to eradicate. While these pests are difficult to spot, dogs, with their acute sense of smell, have proven to be excellent at detecting them. In 2008, researchers from the University of Florida trained dogs to identify the scent of bed bugs and their eggs with 97.5% accuracy. The dogs could distinguish live bed bugs and eggs from their skins, dead bugs, and feces. However, in real-world situations, bed bug-detecting dogs sometimes alert to areas where no bugs are present, leading to wasted time and money for consumers.

7. Cancer

In 2013, a 75-year-old man visited his doctor after his dog persistently licked a small lesion behind his ear. The lesion turned out to be malignant melanoma, and this wasn’t the first case of a dog detecting cancer in a human. Different types of cancer have distinct odor signatures, and some researchers suggest that identifying cancer through its odor—possibly before a tumor becomes visible—could help catch the disease at an earlier stage, potentially improving survival rates. The Penn Working Dog Center’s cancer detection program is training dogs to detect odors from tissue and blood samples of ovarian cancer patients. Researchers aim to isolate the odor the dogs detect and develop an electronic sensor to screen for cancers earlier.