How Do Cadaver Dogs Recognize Human Remains?

Cadaver dogs can pick up the distinct scent of human corpses from a pile of rubble or deep underground. With their exceptional abilities, these canines help recover victims of natural disasters and even solve crimes.

Certain breeds, such as shepherd dogs, are more commonly used as cadaver dogs, but according to Clément Martin, a researcher at the Belgian National Institute of Criminalistics and Criminology, there is only one feature that excludes specific breeds from this career path: snub noses. When snub-nosed dogs breathe, a lot of air goes into their mouths instead of noses, Martin explained, and that negatively affects their ability to detect odor molecules. “If you have a medium- or long-snouted dog, it makes no difference,” he said.

While there’s no doubt about cadaver dogs’ uncanny abilities, scientists are still digging into the chemistry of decomposition to understand what makes these dogs such reliable corpse sensors.

Sniffing Out Cadavers’ Signature Scents

Legal restrictions often limit the availability of human bodies for cadaver dog training. Some countries, such as the US, allow the operation of “body farms,” outdoor spaces in which forensic scientists can study human bodies as they decompose under various circumstances. These facilities contribute significantly to cadaver dogs research and training, though they are heavily regulated and are often quite restrictive.

In other places, such as Belgium, where body farms are illegal, handlers need to be more resourceful in finding things that they could use to train their dogs. For example, many consider pig tissue as the closest substitute for human flesh and use it to train cadaver dogs.

In a 2015 study, researchers analyzed volatile organic chemicals (VOCs) released by decomposing corpses of different animals, including humans, using mass spectrometry.¹ They discovered nearly 500 VOCs across approximately 15 species, but only eight compounds differed between pigs and humans. Among these eight, five were only found in human remains.

“In my opinion, it’s impossible for [cadaver] dogs to tell the difference between pig and human [remains],” said Martin.

Recently, Martin’s team tested the ability of four trained cadaver dogs to detect the five unique human VOCs.² The researchers prepared blends with different concentrations of the five VOCs, in hopes of formulating the perfect chemical concoction that mimics the odor of decaying corpses—essentially a dead human perfume.

They discovered a critical VOC (dimethyl disulfide) as well as the lower limit of cadaveric compounds that the dogs could detect (approximately 100ng). Martin shared that the Belgian police now use this “perfume” as a complementary tool to train cadaver dogs, reporting that it helps the dogs be more precise in their detection.

“Because there are only five molecules to learn, the dogs are more focused,” Martin said. He explained that this allowed the dogs to only search small parts of the training environment instead of screening the whole area, decreasing the rate of false positives.

While the first aim is to minimize false negatives, it is also important to limit false positives. “When there is a corpse, the goal is that we find that corpse,” said Martin. If the searched area has a both a human corpse and a dead pig, and the dogs mark both, “That’s fine, though when you search an entire forest, you do not want your dogs to stop every five minutes,” he added.

Cadaver Dogs Can Train on Donated Amputated Limbs

Another researcher, Rushali Dargan, a chemist at the University of Mississippi, investigated whether amputated limbs could be good training aids for cadaver dogs.³ Dargan started this work when she was a graduate student in Canada. The country legalized body farms in 2019—Shari Forbes, Dargan’s PhD advisor, set up and leads Canada’s first facility—but Dargan said, “ethically obtaining human tissue is a lot of times still problematic outside the US.” Amputated limbs donated by living individuals may help circumvent the issue.

In a recent study, Forbes's team, led by Dargan, stored amputated feet either at room temperature, in a refrigerator, or in a freezer. They found that cadaver dogs that had been trained using human remains positively identified loose feet from all conditions about 98 percent of the time. This supports Dargan's hypothesis that amputated limbs could indeed help train cadaver dogs.

When the researchers analyzed VOCs released by the amputated feet under different decomposition conditions, they observed those previously associated with decaying remains. However, one of the prominent VOCs in the feet stored in a freezer had likely originated from the anesthetic that was delivered during the amputation surgery, suggesting that storage conditions may affect VOC profile.

“I think handlers should train cadaver dogs on all sorts of storage conditions, because then, they’re learning decomposition and not a specific storage condition,” said Dargan.

The Future of Cadaver Dog Research

Martin hopes that someday, scientists can understand how cadaver-associated molecules bind to receptors in dog noses and how this binding, in turn, affects the molecules’ structure and chemistry. “It’s pretty fundamental, but I think when we understand this activation of receptors, it will be easier to select specific things to train cadaver dogs,” he said.

Knowing the exact stimuli that cadaver dogs pick up may also advance researchers’ efforts in building “electronic noses.”⁴ Martin said, these chemical sensors are not meant to replace cadaver dogs but rather as stand-ins that could go to places that are inaccessible or too dangerous for dogs.