Welcome to Science of the Scare! Every month I will dissect a Big Science Question from a horror movie and talk through it in (mostly) easy-to-digest terms.

Science and horror have a wild, entangled history and have left us with loads of questions to ponder. Deep, important questions like: just how many ways could we have a zombie pandemic? Is genetic engineering always a slippery slope to monstrosity? This month’s Big Science Question:

Can someone actually make perfume to capture women’s scents?

This month’s question comes, of course, from Cold-Blooded Killer Jean-Baptiste Grenouille, featured in Tom Tykwer’s 2006 film Perfume: The Story of a Murderer. Grenouille (Ben Whishaw), a strange man without a scent of his own (more on that later), is an “olfactory genius” obsessed with distilling the perfect perfume. His obsessions lead him to stalk and murder women to capture their fragrances. In particular, he prizes the scent of a beautiful red-haired woman (Karoline Herfurth). But in real life, would Grenouille‘s scent-making technique work?

The short answer is: Yes. Yep. Totally.

In fact, it’s been done.

Diffusion de Rabot, a project completed by artists Lotte Geeven and Yeb Wiersma, collected the scents of 100 people by having those people wear sterile T-shirts for a day and then extracting scents from the sweat deposited into the fabric. Another project, done by Mediamatic, an art centre in Amsterdam, actually requested red-headed women to contribute their scents in a similar manner.

These projects didn’t have to kill anyone to make these perfumes; Grenouille just killed people to capture their fragrances because he’s a big ol’ murderer.

The technique that Grenouille uses is known as cold enfleurage. It’s a real, old-school process for capturing scents. It’s also really time-consuming. There are two steps to the process: step one has the scent sample (usually flower petals) being pressed between two panes of glass that have been coated with fat. The fats dissolve the volatiles (the molecules that smell like something) and then in step two, those scents are extracted from the fats using an alcohol (specifically, ethanol). The result is what’s known as an absolute (sort of like an essential oil, but essential oils are created using a different process).

Humans can’t be pressed between panes of glass easily, but since time isn’t a concern for Grenouille‘s victims, he can just leave them for as long as required for the fats painted upon their skin to absorb enough scent.

What makes a human scent, anyway? Stinky feet and armpit smells are the result of microbes living on your skin feasting on your sweat and producing foul-smelling waste products. That’s one of the reason’s why it’s so weird that Grenouille doesn’t have a scent. The idea suggests that he’s somehow sterile and void of sweat-munching bacteria (or maybe even void of sweat). The idea of microbe-free skin would pose a ton of problems with Grenouille‘s system, since those microbes are actually part of our skin’s line of defense against microbes that could make us sick. Grenouille may not have a smell, but everyone else in Perfume does (as they should!). While the profile of your own sweat is sort of personalized by the exact balance of microbes that make up the flora on your skin… that can’t be all there is to human scent, right?

“These projects didn’t have to kill anyone to make these perfumes; Grenouille just killed people to capture their fragrances because he’s a big ol’ murderer.”

Enter the mysterious human pheromone. Pheromones are chemical signals produced by a body to communicate with other members of the same species. We see them in all sorts of animals, and we’re pretty sure that humans produce signaling chemicals, too, either for bonding or for sexual signaling. But so far, the chemical that we can safely call The Human Pheromone has proved elusive to scientists. Some hormones, such as human steroid molecules androstenone, androstenol, androstadienone and estratetraenol, have been proposed as Human Pheromone candidates, but studies (including plenty of research that asked people to smell sweaty t-shirts), have so far been inconclusive. For a molecule to conclusively be labeled a pheromone, it has to meet very specific criteria:

pheromones are not individual scents (so, you can’t use pheromones to tell people apart; one person just might have greater concentrations of that pheromone that others, to a stronger effect);

pheromones elicit a stereotyped behaviour from those to perceive it (like aggression or sexual attraction) and you have to be able to measure this consistently.

The concept of a human pheromone is further complicated by the fact that humans don’t seem to have functioning vomeronasal organs — the organ found in other mammals to perceive pheromones. Even if we are putting down human pheromones, it’s unclear how other humans can possibly pick them up. Maybe we were able to perceive pheromones at some point, but lost the talent to evolution.

“Some hormones […] have been proposed as Human Pheromone candidates, but studies […] have so far been inconclusive.”

Grenouille‘s perfected perfume was able to consume crowds and stir them to a sexual frenzy. We’re supposed to assume that the pheromones of beautiful women were able to create such a powerful effect. Imagine if the human pheromone perfumes that you can buy online could do that. (If it isn’t obvious by now: please don’t waste your money on perfumes that claim to use human pheromones. Yes, they really exist. No, they don’t work.)

Have a Big Science Question from horror that you’d like to see answered? Let us know over on Twitter, Reddit, and in the Horror Movie Fiend Club on Facebook!