Digging into the Chemistry of the Creepy Smells of Blood, Death, and Darkness

When we think of scary, we ordinarily think of the sights–dark hallways and spider webs, bloody masks and crumbling gravestones, and to a lesser extent, sounds–creaking doors and spooky voices–cue Vincent Price’s Witchcraft Magic!–but what about creepy smells? So many write about the nostalgic scents, the comforting ones     of kitchens and gardens, lime-flower tea and madeleines, but what about those creepy smells we prefer to avoid or forget–those of blood and the grave, caves and decay? What makes them provoke discomfort or fear?

Let’s begin with the smell of blood, described in countless novels as possessing a kind of metallic tang. Though the scent of blood is a cocktail of chemical constituents, one molecule has been isolated, and has been shown to attract predators and repel prey across species, even across phyla, from wolfs and flies to mice and humans. It’s an aldehyde called trans-4,5-epoxy-(E)-2-decenal, thankfully abbreviated to E2D. Experiments conducted at Kolmården Wildlife Park in Sweden, involving four predator species– Asian wild dogs, African wild dogs, South American bush dogs and Siberian tigers –show that the isolate provokes the same response as blood itself, according to this article at Science Daily.

For those interested in perfumery, you may recognize the word aldehyde as a classification of aromachemical molecules that often give us pleasant odors, such as cinnamaldehyde, the main constituent in cinnamon, and anisaldehyde, the main constituent of aniseed. (Chemists are not super original with their naming, which is probably a good thing!). Another common aldehyde is formaldehyde, which has a creepy scent all its own.

The Swedish researchers teamed up with others in the US to explore the effects of E2D on predator/prey relationships. Subsequent experiments showed that blood-sucking flies were also attracted to the scent of the isolated molecule, and that mice were repelled. Interestingly, humans react to the scent as prey rather than predators, which makes sense, if you consider the fact that, for most of our species’ existence, we spent a lot of time running away from lions and tigers and, um, kangaroos, according to this article at Slate. “Humans were eaten by giant hyenas, cave bears, cave lions, eagles, snakes, other primates, wolves, saber-toothed cats, false saber-toothed cats, and maybe even—bless their hearts—giant, predatory kangaroos.”

Returning to our E2D blood molecule, this article at Forbes describes the experiments done with mice and men: “Human participants of the study stood on a strain gauge force plate, which detects minute changes in balance, and were exposed to E2D. Although E2D has a neutral scent and not at all unpleasant, the participants consistently leaned back ever so slightly (around a millimeter), a hallmark avoidance behavior.”

By the way, it should be said that humans supposed poor sense of smell is a myth impressed upon us by nineteenth-century scientists to distinguish us from our mammalian relatives, as convincingly argued in this Science research paper. When a variety of odors is used to compare human olfaction with other mammals, “the results are strongly influenced by the selection of odors tested, presumably because different odor receptors are expressed in each species.” That is to say, that in certain cases, humans outperform laboratory rodents and even dogs. “Like other mammals, humans can distinguish among an incredible number of odors and can even follow outdoor scent trails.”

Let’s move on to the smell of darkness. Darkness has a smell? Yes! By darkness I mean spooky caves, graveyards, and basements. Intrepid Etsy candle makers are capitalizing on just such smells. Take for example the Brooklyn-based Grizzly Candles who sell Creepy Basement, the description of which deserves some space:

Whether you had one that scared you as a kid or were just terrified by a relative’s whenever you visited, having to enter an unfinished basement (the scary creepy kind) was always a mental battle lost.

Cool yet humid, damp yet dry, our Creepy Basement brings you back to that exact moment of slowly walking down those dark wooden stairs, fear tightening in your chest and your mind playing tricks on you as you quickly ran to retrieve whatever had fallen down there.

I’m guessing that somewhere in that bone-chilling basement smell there is the quintessential wet dirt molecule that chemists isolated as geosmin. This molecule is largely responsible for the earthy taste of beets and the smell of dirt after a rain, or technically, petrichor. We’ve considered wet pavement before and called the smell lovely, but as with indole, so much depends on context. The smell is creepy in cellars, graveyards, and caves.

In fact, geosmin gives my favorite perfume, Bat, its dark shimmering greyness. As we mentioned in our review of Perfumes: the Guide 2018, the creator of Zoologist’s Bat is Ellen Covey, a neuroscientist who has clocked many hours in bat caves studying echolocation. “I just got my hands on some geosmin aromachemical before I made Bat,” Covey said in an interview, “and used it to help create the cave smell.”

Speaking of perfumery, indole is a chemical compound found in white flowers such as jasmine and ylang-ylang, but it is also found in Halloween’s other favorite plant, the corpse flower, which uses its smell of rotting meat to attract carnivorous creepy crawlers. For more on the corpse flower and its strange nocturnal niche, check out The Corpse Flower and Goethe.

“Shit is full of indoles,” explains the eloquent perfumer Jean-Claude Ellena in The Perfect Scent by Chandler Burr, “and so are decomposing human bodies—the decay creates indoles; they’re the molecules you smell when you smell a corpse.” Ellena calls death “a feminine scent,” which from a perfumer’s standpoint may ring true: Jasmine and ylang-ylang are not often found in masculine concoctions. Still it’s a bold statement!

Ellena then refers to Calvin Klein’s Eternity, crafted by the legendary perfumer Sophia Grojsman of IFF, which is apparently one of the most heavily indolic perfumes around, and points out the irony of a perfume called Eternity smelling like death. Ironic perhaps only to some not spiritually minded. It seems to me that most major religions are founded on the premise that physical death leads to spiritual eternity, but perhaps I’m reading too much into it.

In any case, it’s interesting to me that some of the most heady and erotic flower smells–try to find an aphrodisiac blend that does not contain either jasmine or ylang-ylang, or both!–are also the flowers that contain the most indoles, indicating the close relationship of sex and death, no better expressed than by the French term for orgasm, “la petite mort,” literally “the little death.”

So, this Halloween, why not stretch beyond the chocolates and pumpkins, and really spice up your parties with creepy smells? And, who knows, your costume might be that much more scary (or sexy) if you dab yourself with the right scent…