This essay is part of Scent Access Memory, our editorial series with Dirt.

My high school’s science lab, that site of boredom and horror, haunts me still. I can conjure the fetal pig, pale and waxy on its side, eyes closed or not yet lidded, its legs joined in pairs as if to protect the bloodless incision along its abdomen that I don’t recall making but that must have been my work. It lies on a squishy medical-blue mat set within a cold metal tray large enough for me to shift the animal, which seems somehow born and unborn, onto its back and spatchcock it, now fixing it into place with the thick needles my classmates and I have been given for this purpose.

But such details, however lasting and privately vivid, don’t carry much charge for me anymore. What does is the smell. 

When I think of formaldehyde, this is what comes, a stench at once sharp and oily, antiseptic and like something no hospital would ever tolerate. With fragrant materials, dilution can make their key characteristics discernible, and time’s passage has served the diluting function here; the trace amount of formaldehyde that has stayed in my mind is merely a potent extraction. But if the smell has achieved some depth and dimension in the years since, back then it was impenetrable and total, so strong that it seemed to emanate from every object in the room, from the beakers to the matte-black countertops. I would have believed that formaldehyde’s smell alone was the preservative agent, for it was enough to pickle the air around me. And the smell meant only one thing: not decay, but decay’s arrest. 

Formaldehyde belongs to a class of molecules of which it is arguably the best known: aldehydes, compounds which include a carbon atom bonded to oxygen and hydrogen atoms. Among aldehydes, formaldehyde is uniquely carcinogenic and wretched; as you add carbon bonds, the molecules become pleasant to the nose. 

There is a subset of perfumers and perfume aficionados for whom the word “aldehyde” more readily brings to mind a dazzling hit of dodecanol than the reek of an open casket. Aldehydes are a common, even quintessential, ingredient in modern perfumery. Unto themselves, they’re prominent and assertive, and they can thusly dominate the opening of a perfume—what the wearer immediately detects after the first spray—but because of their volatility, they become less detectable shortly thereafter, giving way to the more enduring aspects of a perfume’s composition, its middle and base notes. 

Aldehydes are particularly common in perfumes derisively referred to as “old lady,” Chanel No. 5 being the most obvious example. The story of the iconic perfume’s conception is inextricable from aldehydes, and its continual retelling has ironed it into myth. Here is a common version: that one of the lab techs compounding the formula requested by Chanel’s perfumer Ernest Beaux accidentally overdosed it with aldehydes, and Coco was taken with the result, now one of the greatest selling perfumes of all time. 

In Chanel No. 5, aliphatic aldehydes give the perfume its effervescent character, often described as “shimmering” or “sparkling.” Such descriptors regularly attach to aldehydes in general, and with enough frequency that a writer can neither claim them nor claim to have copied them—they simply arrive with the raw material, along with words like “soapy” and “fatty.” On Fragrantica, aldehydes are represented not by their molecular shape but by an image of a blindingly bright sun in a mostly cloudless sky, so bright that it could scour away any mold it finds. 

However, the fact that “sparkling” might not conjure much, olfactorily speaking, for someone not already obsessed with perfume suggests one of several difficulties one faces when trying to write about smell: that the writer is largely confined to description by comparison (a perfume can smell of apple, but mentioning this feels as pointless as trying to define a word using only synonyms), and to description by figuration (a perfume can be “dark,” “cold,” “soft”). Just when I think I’m beginning to understand the way in which Chanel No. 5 “sparkles,” I doubt myself: am I simply learning the word that goes, somewhat arbitrarily, with the effect that I’m perceiving? (Yes, is the answer.)

And there’s another difficulty, this one specific to aldehydes: the sheer variety of aldehydic smells. In addition to smelling of high school science labs, aldehydes can smell of peach, cardamom, strawberry, the interiors of new cars. Certain aldehydes smell industrial while others smell soapy, although these characterizations are perhaps tautological, given how common aldehydes are in building materials and scented cleaners. This variety may not be entirely random: in his book The Emperor of Scent, Chandler Burr cites “perfume genius” Luca Turin, the book’s dyspeptic subject, who suggests that an even number of carbon bonds in an aldehyde correlates with a fruity or citric smell while an odd number correlates with a “waxy” smell. (To make such scientific claims about how things smell requires a wholesome and self-confident perceptual rigor, the likes of which may only be available to rare, stubborn types like Turin.)

** 

Neither of my parents wore perfume when I was growing up, and so the early perfume memories I have are scant, almost exclusively involving my tiny body being drawn into a fragrant embrace by an elderly relative or family friend, promptly encasing me in whatever perfume she was wearing. I associate aldehydic perfumes with these hugs, affectionate and patronizing and not altogether consensual, cut through with the adjacent smells of roasted meat.

While I can now appreciate the beauty of such perfumes (indeed, their beauty was likely the main reason these women wore them), I for years after understood their principal appeal and purpose as masking the organic smells of age and decay—smells that my own body will, if I’m lucky, produce with increasing alacrity for the decades to come and which I may choose to dissemble with a nice soapy floral perfume. 

But how strange that what conceals the smells of aging can become the primary smell of aging—that aldehydic brightness can be more evocative of getting and staying old than the various musks and funks that our weathering bodies confect. This process of association is not unlike the one we undertake with language, whereby a figurative word like “sparkling” is mentioned often enough in relation to a certain quality that the connection between the two becomes automatic, the signifier and the signified so tightly coupled that they form a new whole. And not unlike the process by which formaldehyde, that powerful preventer of decay, becomes death’s signature scent.