Although being able to distinguish the unique smell of decomposing human flesh may not be high up on your to-do list, the ability to tell the smell of a rotting human from that of a rotting animal plays an important role in our ability to find missing bodies following crimes and natural disasters. In a recent study, however, researchers were able to identify specific chemical compounds associated with decomposing humans, which could help develop better ways to search out human cadavers.

If you’ve ever been unlucky enough to catch a whiff of a dead human body, it’s something you’re not likely to have ever forgotten. However, when it comes to describing what exactly you just smelled, things can get tricky. According to a recent study currently published in the online journal PLOS ONE, researchers from the University of Leuven in Belgium are getting closer to identifying that certain je ne sais quoi of rotting human flesh after identifying key gases emitted during the decomposition process.

For the project, analytical chemist Eva Cuypers and her team set aside samples of human tissue in a jar to rot in a closet for several months, Science magazine reported. The researchers would periodically take samples of the air from the jars in order to analyze the various gases released during the decomposing process. Samples of pig, mouse, mole, rabbit, turtle, frog, sturgeon, and bird tissues were also observed as they decomposed.

To the untrained nose,  all dead and rotting organisms smell more or less the same: disgusting. However, on a chemical level different animals give off entirely different odors. Science magazine reported that the scent of decomposing pig flesh is most closely related to that of humans because we have similar microbes in our guts, the same percentage of body fat, and similar hair.

Analysis of the gases collected from the different decomposing specimens revealed a clear chemical and unique chemical byproduct given off by each organism. Over the course of six months, Elien Rosier, one of Cuypers’s graduate students, was able to collect 452 organic compounds given off by the decomposing specimens. However, of these, eight compounds were only found in the flesh of pigs and humans, and five compounds were found to be unique to human flesh. According to Agapios Agapiou, an analytical chemist at the University of Cyprus in Nicosia who was not involved in the study, this is the first time scientists have been able to understand the differences in decomposing human and pig flesh exposed to the exact same conditions.

Although a cadaver may no longer be alive, its decomposing flesh is anything but dead. Instead, it's filled with an array of bacteria and enzymes that begin to break down the flesh. The bacteria help to break down the dead flesh by eating away at it, and an awful-smelling gas is the byproduct of this process, How Stuff Works reported.

The Belgian Disaster Victim Identification Team asked the Leuven researchers to investigate gases associated with human decomposition in the hopes that identifying these gases would lead to more effective ways of finding lost bodies.

“The mixture of [these] compounds might be used in the future to more specifically train cadaver dogs,” Cuypers explained, as reported by Science. “The next step in our research is to see whether the same compounds are found in buried, full decomposing bodies in the field and to see whether dogs trained on the mixture respond more specific[ally] to human decomposing bodies.”

Along with helping to better train canine, understanding the chemicals involved with human decomposition could also help to develop artificial body sniffers. As reported by the Daily Mail, researchers are currently working on developing “electronic noses” that would theoretically detect the compounds of decomposing bodies in order to help locate victims of natural disasters of murder. Although there are many shortcomings in this still early stage of research, the team believes its recent work is a step in the right direction.

Source: Rosier E, Loix S, Develter W, Van de Voorde W, Tytgat J, Cuypers E. The Search for a Volatile Human Specific Marker in the Decomposition Process. PLOS ONE. 2015.