Sniffing Out Warnings From the Scent of Death
Decomposing animals—and humans—release a pungent mix of chemicals that emit a distinctive odor. In animals, this “scent of death” has been shown to act as a chemosensory warning of danger in the area. Psychologist Ilan Shrira and his colleague tested the human reaction to one particular compound found in decaying corpses, called putrescine, in a study published in the journal Frontiers in Psychology. Shrira explain how even low levels of putrescine might increase our defensive responses.
Ilan Shrira is an Assistant Professor of Psychology at Arkansas Tech University in Russellville, Arkansas.
IRA FLATOW: If you’ve ever smelled rotted flesh, the scent of death, it’s hard to forget. In animal studies, it’s been shown that that particular smell is more than just repulsive, it can actually set off a warning signal in the brain. And now, a team of researchers wanted to know if this happens in humans, too. And they picked, of course, a college campus to test this out.
My next guest is a co-author on the results, published in the journal Frontiers in Psychology. Ilan Shrira is a visiting psychology professor at Arkansas Tech University in Russellville, Arkansas. Welcome to Science Friday.
ILAN SHRIRA: Thanks. It’s a pleasure, Ira.
IRA FLATOW: It’s our pleasure. You’re a psychologist. Why are you interested in testing the scent of death?
ILAN SHRIRA: That’s a good question. I’ve done some stuff. I and my colleagues have done some stuff on death more generally, how it is sort of affects us and affects our psyche when we think about it. And then, we got interested in the sense.
And we’re sort of interested in the similarity between animal models and human models. So we learned about some research on animals that exposes– and you described it very well in the introduction– that the scent from decaying bodies, the rotting flesh.
And we started by isolating one of the signature components, the signature scent, called putrescine that is just released when the breakdown of rotting tissue, rotting flesh. So it smells very rotting.
And so we ordered some of that through a chemical company. And we used that to prime people, expose people, to that and wanted to see how it affected people, just focusing on humans.
IRA FLATOW: And how did it affect people?
ILAN SHRIRA: It affected people. We were mostly in the ways that we thought primarily that it seems to be the exposure to the scent of death. I mean, first of all, in animals, obviously scent is a much more primary, dominant sense than it is in humans. So other animals are going off scent more than we humans are.
But in animals, this exposure to putrescine does cause certain specific behaviors across animal species, particularly avoidance and escape behaviors– getting away as though there’s some sort of danger, either with nearby predators or possibly the risk of contracting an infection from the dead bodies, from the carcasses.
So there’s a tendency mostly to flee the area. And in some cases, because there might be predators around, just to more generally increase vigilance and the potential for readiness for aggression should animals encounter it in those situations.
IRA FLATOW: Talking about the smell of death this Science Friday from PRI, Public Radio International. Talking with a psychologist who studies this, Ilan Shrira. Tell us, if this sort of a pheromone. You know, we know pheromones are those smells that people give off. Is it the same thing?
ILAN SHRIRA: Pheromones are a bit different. We were careful not to use the term pheromones, because in the scientific world, it’s used in a very specific way. And it’s used as a means of communication between two organisms, within the same species usually.
But it’s almost always something that’s released through bodily fluids while one is alive, like most notably body sweat, saliva sometimes. So it seems to be a way of communicating, much in the same way as visual forms of communication or languages. Whereas, putrescine is something that is communicated not necessarily intentionally after one person has died.
IRA FLATOW: And it’s really a strong pungent odor. If you smell it once, you know it forever.
ILAN SHRIRA: Yeah. It’s distinct. I mean, just as the scent of corpses and carcasses is very distinct and powerful, I guess it’s sort of difficult to describe. But it does definitely smell rotten. And to me, it’s distinct that it sort of has this weird unpleasant fishy smell. There are different rotting smells. Go ahead.
IRA FLATOW: In your study, you expose people to, I understand, putrescine or some ammonia to test the difference whether they would run away or not. And you found out that they really do avoid the putrescine.
ILAN SHRIRA: Yes. That was the interesting thing. We wanted to make sure, first of all, there wasn’t just an unpleasantness that they were trying to escape from. So ammonia is something, it’s an unpleasant scent. It’s commonly used in scents studies as an aversive stimulus.
And so, yes, we found we exposed people to ammonia, putrescine, and then a control condition– just water. And after smelling the putrescine, people were quicker to walk away forever.
So we did the experiment outside on campus. We approached people. And after they did this scent test and they rated the scent on different dimensions.
And they subjectively rated the ammonia and putrescine as just about as equally repulsive and unpleasant. But when they walked away, we sort of had somebody waiting in the bushes behind the tree and clocked them. And after smelling the putrescine, they were walking away a bit more than 10% faster in distance.
IRA FLATOW: Wow.
ILAN SHRIRA: Than the ammonia even.
IRA FLATOW: And this is something you can do at home. If you want, you can buy these odors from a lab supply house. It may be a little late for Halloween. I don’t know. Overnight shipping?
ILAN SHRIRA: Maybe.
IRA FLATOW: Thank you very much, Ilan, for taking time to be with us today.
ILAN SHRIRA: I appreciate it. It was a pleasure.
IRA FLATOW: Ilan Shrira is a visiting psychology professor at Arkansas Tech University and Russellville, Arkansas.
One last thing before we go. A couple of weeks ago, we talked about Halloween hacks with spooky projects you could make from slimy eyeballs to remote-controlled skeletons. And we asked you for your own thoughts. And here is one that was sent in.
SPEAKER 1: What we have is a ghost mobile. It is suspended from a branch about 60 feet off the ground with a 60-pound strength fishing line and hangs from two sticks– one large one and one medium size one. The ghosts are life sized. They are made of Styrofoam wig heads covered with cheese cloth.
And the shoulders and arms are hinged so that they move like real arms. And they have counterweights on them so that they wave realistically. When the wind blows, this mobile goes all over the place and does all kinds of fancy things that people to watch.
IRA FLATOW: So if you need a last-minute Halloween ornament or something like it, you can build that spooky ghost mobile.
Alexa Lim was a senior producer for Science Friday. Her favorite stories involve space, sound, and strange animal discoveries.