You can’t miss the Monell Chemical Senses Center building in West Philadelphia. It’s the one with an enormous golden nose jutting out of the building by the front door. A daring move, even for a center of taste and smell research: the triangle of skin and cartilage that fronts our faces is not widely admired. I have come to Monell to speak with an olfactory scientist, but I pause at the nose for a while and just look at it. How strange the nose is. While the human face looks bereft without a nose, it looks fairly silly with one. With our species’ affection for gazing into each other’s eyes and our focus on kissing or stuffing food into our mouths, we nearly overlook the organ in between. Well, not entirely. We break our noses; we surgically fix our noses; we pick our noses; we powder or sunscreen them. The nose leads our face as we walk and fills our bedrooms with snores as we sleep.
But it is often unlovely and largely unloved. It is reduced to an upside-down 7 by a child’s hand, and may never evolve beyond this rendering. It is the stepchild of the face—the overlooked space between more esteemed anatomical parts.
For a facial feature that is so conspicuous, so apparent that it prompts its own aphorism, the nose is surprisingly unfamiliar to us. We might gaze at a cute turned-up nose or a prominent bulbous nose. We might suffer a sinusitis that arrives with the pollens of spring. Surely we savor the rush of dinner smells that hits us when we arrive home, just as we bristle at the wash of sewage odor emanating from the so-called sanitation department’s hub.
We have many fanciful—if moderately obscure—words for nose in English. The beak, nozzle, snoot, beezer, bill, gnomon, nib, snot-gall; occasionally rendered as a bowsprit, a vessel, a boko, a snooter. The snitch, trunk, index, horn, the spectacles-seat. What we do not have is much knowledge about what happens after we sniff with that scent-box. Most of us know little about the smells of our world, little about how the nose takes in odor, and even littler about the smell system of the human brain. Scientists, surprisingly, feel the same way. George Preti, the researcher at Monell whose group studies primarily “human odors,” found the territory relatively untrammeled: “They were probably the last thing that chemists tackled for some reason.” Scientific knowledge is only nose-deep, another olfactory researcher, Dr. Leslie Vosshall, told me: “The basics are easy,” she said, “and then the hard stuff [about how smell works], we have no idea.”
“Nobody knows about olfaction,” Stuart Firestein consoles me, as I admit that I haven’t thought much about smelling in all my forty-some years. His statement extends not just to the layperson, but to biologists, and even olfactory neuroscientists like himself. Human olfaction was one of the last sensory systems to receive the scrutiny of science, upstaged by vision—how we love and admire our eyes!—and even the bench team, hearing and taste. But it deserves a look. It is not a coincidence nor an accident that we, dogs, sharks, and voles have noses. Noses house special cells that allow us to smell—and smelling is an evolved strategy to find out more about the world.
Smelling dates back to the ancient and single-celled prokaryotes, enabling them to avoid things that are toxic and head toward things that are beneficial. Today almost all living creatures in air, sea, or on land can smell in some way.I Smelling is chemosensation, the detection of chemicals, and we live in a world of chemicals.II The nose, then, is for seeing them, and figuring out which to pursue and which to avoid. “The biological nose,” Firestein has written, “is the best chemical detector on the face of the planet.” At the same time, he admits the olfactory system “is probably, like everything else in evolution, a bit of a kludge job”—a few systems all plonked in or around the nose, doing more or less the same thing, though in slightly different ways.
Humans have an odor problem. It involves our use of smell (scanty when compared to many other animals). Primates, including the human primate, are considered microsmatic—what is (probably unfairly) called feeble scented—as contrasted with macrosmatic dogs.III It involves our cultural sensitivities about smell (given that artificially scented “air fresheners” are not considered ironic or aberrant). Smell is reliably the sense that people suggest they would be most willing to lose. But also, most fundamentally, our aversion comes from a deep misunderstanding of smell. We distrust smells. Invisible somethings find their way into our noses: it can feel horrifying at worst, peculiar at best. Though we will put all manner of steaming, dripping, oddly colored foodstuffs into our mouths with alacrity, we can feel embarrassed, alarmed, or disgusted by an odor showing up in our noses.
The invisibility of odors accounts for some of this reaction. We rarely search them out; we more often experience them happening to us, catching us unawares. And there is uncertainty about what smells actually are. Here’s what they are: they are molecules, flowing about in the air. Since the world is molecular, they can come from just about anything—gases, liquids, or solids (which continuously release a haze of molecules into the air).IV In particular, biologists specify that odors are “small, low-molecular weight organic molecules.” These molecules also must be a certain amount volatile—able to evaporate into the air, be caught by a nose, and cause the sensory cells to hum and purr. When we smell something, we are really ingesting it, after a fashion: the molecule is being absorbed by the mucus layer of the nose. In this way smell is different than our other, less alarming senses: what we see (through light reflecting into our eyes) stays out there; what we hear (through vibrations drumming our ear canals) ends at the ear; what we feel does not burrow into our skin, but glances off it. But in smell a bit of the source itself comes into our bodies.
Most adults see smells as incidental, and as binary—very good or very bad. “The principal axis of human odor perception,” write neurobiologists struggling with our detachment, “remains odor pleasantness”—whether we like a smell or not. Not only the unwashed masses but also “the greatest poets in the world,” wrote Virginia Woolf, “have smelt nothing but roses on the one hand, and dung on the other. The infinite gradations that lie between are unrecorded.” Sigmund Freud came out on the “very bad” side in general, equating the diminishment of our olfactory powers with the rise of our rational minds. “The organic sublimation of the sense of smell,” he claimed, “is a factor of civilization.” Sights are information; smells are judged. Smelly never means anything but “stinking.” We like those who smell like our own social group and distrust those who are “smelly.” “Being odorous,” writes Jim Drobnick in The Smell Culture Reader, “is tantamount to being odious.”
None of us began life smelling so monochromatically. We are born smellers. In early development, nasal chemosensors emerge before any other sensory system. And we have been in contact with odors from the get-go: as fetuses, we are in a wash of fluid carrying the odors from our mother’s food. By birth the olfactory nerve is intact: better to search for the smell of mother’s nipple and the milk it promises. Tiny glands around the nipple send beacons to the baby’s nose.
In our first hours and days, we are tiny but macrosmatic animals, exploring by nose more than by sight. A newborn recognizes his parents by the cloud of fragrance coming off them; his vision is still too blurry to see them clearly. A child’s security blanket, or any favored raggedy, one-eyed teddy bear, is so loved due to its smell. If washed, it is changed—and sometimes rejected. Children are ambivalent about what adults find to be clearly horrible smells: they must learn to hate the smell of spoiled milk and flatus. They don’t know that “skunk” is a bad smell; that “flower” is terrific.
But now, reader, take a moment to consider: What have you smelled today? Chances are, nothing. And if anything, it was involuntary—the baked bread as you entered the house, the thoroughly-sodden-dog smell that you’d sealed up in your car after that trip to the lake yesterday. When I ask people what they have smelled today, I often get a lot of searching looks. By adulthood, we have mostly forgotten that smell developed as a means of discovery. Most animals—our ancestors among them—use smell purposefully: to sniff out potential mates, to find delicious and nutritious food, to notice predators before being noticed. We have not entirely neglected these important discoveries, but instead of smelling a person, we smell his shampoo; the food is not found in the wild, but cinnamon buns and pizza joints can be navigated to by nose; and while we might not smell danger, we know the acrid smell of smoke and the added smell (the rotten-eggy compound mercaptan) of natural gas.
To restore smell to its rightful place we must undertake a simple three-step process: first, notice the smell at all. We must sniff it in, let it settle into the warm lining of the nose and snuggle into a receptor cell. Second, we have to be able to distinguish the smell from other smells—to simply note and remember their differences. Finally, we want to name what it is, or locate its source.
To begin, we’d better be clear about our noses.
Nosed animals come in terrific varieties: mollusks smell with their tentacles; male silk moths with their feathery antennae; the simple nematode worm detects chemicals via an opening near its front tip. The elephant’s periscopic sniff is enabled by its trunk—which is also used to examine objects and to caress other elephants. The domestic pig’s nose has expanded into a perfectly lovely implement for rooting around. Star-nosed moles have a spectacular, fleshy nose with twenty-two radiating appendages that function as tactile sense organs, doing no smelling at all. Semiaquatic animals like the water shrew blow air bubbles to trap scent and then re-inhale the bubbles to smell them. Leslie Vosshall and her colleagues at Rockefeller University discovered that the mosquito repellant DEET works on the insects’ “nose”—receptors on its antennae. The repellant is a “molecular confusant,” they write, that scrambles the message to the mosquito about a warm-blooded target nearby.
The world of nosed animals can be divided into those with hidden noses and those with flagrant noses. We are in the latter group, naturally. Among primates there are also two nose types: the curved noses (strepsirrhines)—think of the cute-faced lemur, with its surprised eyes and tufted ears—and the simple noses (haplorhines) of most primates, including humans. The curved noses have the wet, naked rhinariums of dogs and cats. Among the simple noses, we can be further divided into downward-nosed (hominoids and old world primates) or flat-nosed (new world primates), based on the direction of the nostrils. So we’re a flagrant, simple, downward-nosed creature.
The human nose is, anatomically, a soft organ, layers of skin and muscle, braced only by cartilage and fat on the inside. The outside is rife with sebaceous glands, the inside lined with mucus. A squishy, unwieldy vessel, moist and oily.
And it is just a vessel, most of it. “In man,” Isaac Asimov wrote, the nose is “primarily an air vent and has no exotic uses.” (That might depend on what, exactly, one chooses to smell.) Notably, the exposed “projection in the midface region,” as it is romantically referred to, is not actually the smelling nose. Just as with dogs, while odors are hurried into its dark depths, most of the visible nose is just a cavern and humidifying chamber en route to the treasure of olfactory tissue deep at the back.
The smelling part of the nose—the olfactory epithelium where odors are received and translated into neural signals that make the brain say cake! or kimchi!—is the very end of the cavern. In the depths of the human nose, at about the point where the outer nose flattens into forehead—the midpoint between the eyes—is a postage stamp–sized plot of epithelial tissue. “You can’t reach it with your finger,” Stuart Firestein cautions, as though I might try. Sitting across from me, he wears a look marrying perpetual amusement and skepticism. His whitish hair leans toward unruly, but never delivers on the threat. My fingers stay in my lap, but I squirm reflexively. I make a note to refrain from telling my six-year-old this bit of news.
Let’s not forget the importance of that pyramidal, protuberant vent, though. If it’s congested and the sinuses swollen, smelling is temporarily disabled: we often lose our sense of smell—and thus of taste—when we have a head cold. Food designed for astronauts must be highly spiced and flavorful, for they are permanently congested: the fluid in their heads does not drop nicely toward their toes with gravity. As it clogs them, it deprives them of the enjoyment of what were beloved foods back on terra firma.
The appearance of the outside of the human nose does not reflect its internal architecture. The large-nosed among us have no more tissue dedicated to smelling, relatively, than the tiny-nosed. In both, our olfactory postage stamps are a very small amount of the entire nose. Hence the reason that humans are generally considered poor-smelling: we have less space for olfactory cells, and thus less sensitivity to odors, than macrosmatic animals like dogs. “It’s this little teeny-weeny nose,” Firestein says. “And it’s very, very tight up in there.”
A nasal septum divides the nose up the middle, making two vestibules: the most perfunctory of waiting rooms en route to the back. Each vestibule is lined with special glands that produce up to two liters of mucus a day. This soda-bottleful of mucus helps moisten the air (good for both breathing and smelling) and helps protect against any large or irritating molecules flying up into the nasal tissue. For when you give a good sniff, air flows through the nose at twenty-seven liters per minute—“gale-force speeds.”
The human olfactory system is more developed than we usually admit. But is it near dog levels? Anatomically, the comparison is stark: our nose is smaller and our sniff is less complex. The human sniff is not unlike that of the ancient canid: a bellowsful, a crude, imprecise pull of air in and out. Unlike the modern dog, our sniff is long and slow: we take a second and a half to sniff even once, pulling in as much air as might fill a regulation-sized softball. We have half as many genes coding for olfactory cells, and more of ours are not functional. We have less space for smelling—only one to two square centimeters of epithelial tissue; our noses house hundreds of millions fewer olfactory receptors and half as many kinds of receptors. If there’s less territory to make sense of an odorant, then even if it manages to land in the human nose, our sensation of it goes . . . nowhere. We may notice an odor but not be able to identify, locate, puzzle out, or even react to it, before it dissipates and we move on.
Architecturally, our noses are children’s block towers next to dogs’ modern architecture: made of similar stuff but in a much simpler, more brutalist formulation. While the human nose does hold turbinate bones like the dog’s, there are only three small bones, and they don’t bear nearly as much olfactory tissue. Turbinates in a human nose are like minimalist modern art: simple Miró figures compared to the dog nose’s healthy branching tree. And alas, my friend, you lack the “olfactory recess,” the deepest part of the dog’s nose, partially segregated from the rest. This matters: there is no place in the human nose for air to pull up a chair, sit, and be repeatedly smelled. Some scientists have suggested that with the movement of human eyes forward to the front of the head, we lost the space for a nose alcove. As a result, we exhale any inhaled smell right back out, scrubbing it from the gentle embrace of the receptors. This accounts for the sometime success of our frantic effort to purge a foul smell by blowing our nose.
We entirely lack the vomeronasal organ that forms the dog’s second smelling route: in humans, it is vestigial and disappears before we are born. All our VNO genes are pseudogenes, no longer functional, so we produce no cells, no receptors, and make no connection to the brain. We do not seem to detect pheromones at all. “Sadly,” writes Tristram Wyatt, an expert in all things pheromonal, “there is no good evidence for a human pheromone to make the wearer irresistible to potential partners.”V
Psychologically, we are also different than dogs. We will trust our eyes over our noses. If there’s disagreement between the senses, vision wins. Cherry juice made to look green tastes to us like lime; color a white wine red and even enology students taste it as red. Not only are we largely ignoring the input through our snouts, we sniff so infrequently that only an unusually strong odor reaches our consciousness. Any attention we bring to odors as infants is quickly learned away: “Baby smells an odor, mother says nothing,” Mary Roach quotes a researcher at Monell as telling her. And so baby ignores the next smell coming her way. Our brains develop around non-smell things; the dog’s brain is developed around smells. What the dog ignores, by contrast, is all else apart from the smell he has his nose in. As anyone who has tried to pull his dog from a long investigative bout knows, the dog practices impressive attention. Fitting that the Latin root of attention means “to stretch,” to direct the faculties toward. The dog’s nose stretches in all ways.
Nor do we humans celebrate the intimacy of smell. Should someone be close enough that we can smell him, we find that too close. “Most people in Western cultures don’t smell at social distances,” George Preti tells me—referring to both people’s bodies and their smelling habits. We seem to bathe at levels matching our sense of normal personal space; in the United States, it’s an eighteen-inch buffer radiating from us. Notably, vision and hearing allow for interaction with someone in social space without any violations of personal propriety—we can both see and hear someone comfortably. But to smell them would be intrusive at best. When I ask Preti if he smells people often, he laughs and says: “I don’t want to get smacked!”
Fundamentally, though, our noses work in the same way as the dog’s. As with the receptors in the dog nose, there is no one-to-one odor-and-receptor correspondence. There is no single “vanilla” receptor nor “smoldering cigar” receptor, despite the instant familiarity of each. We specialize in our olfactory sensitivities: some odors we can smell in impressively small amounts, such as the banana-y odor of amyl acetate in .01 parts per million; others need to be thousands of times more intense for us to notice them. We are great at detecting and recognizing coffee, which, like most food and drink, has hundreds of constituent parts, but we are utterly anosmic to plenty of other molecules. Some other animals smell carbon dioxide; we do not. For an especially puzzling case, look at carvone, in the class of naturally occurring chemicals called terpenoids. It comes in two identical forms that are mirror images of each other. One form smells like caraway seeds, the rye bread of an old Jewish deli; the other smells like spearmint gum. Our brains read the same molecule as entirely different smells. Any model of receptor processing tries to bring a rhyme or reason to why a molecule smells the way it does to us.
Our olfactory neurons function just as dog neurons do: they serve to transmit the message of an odor’s arrival to the brain, which then scrambles around trying to figure out what in the world it is. That’s when you “smell” it: when the brain registers there’s something there. In some sense receptor cells “know” what the smell is—insofar as each will allow only specific molecular shapes to bind to it—but they don’t really know. It is the brain that knows (or doesn’t), and that swoons with the rush of a memory of hot chocolate after a long winter’s day playing outside, or balks at a urine smell in the subway, source unseen.
Olfactory neurons themselves are pretty special. In all animals, these cells regenerate about every thirty days. You trade out old summer neurons, which may have conveyed the loveliness of the lavender garden and the rank odor of warmed manure to your brain, for new fall ones, ready for apples fermenting and coats being unmothballed. This fact is extraordinary. Aging usually means deterioration: all our senses dim through damage and cell loss. Our hearing diminishes over time as we damage our auditory cells by the fact of merely living (and listening to loud music through headphones, waiting for subway trains, and standing too close to the fireworks). In the course of a perfectly normal life we age into glasses, then reading glasses, then bifocals. But there is not an odor correlate to staring at the sun, turning the headphones volume to 11, or touching a scorching cast-iron pan. Unlike the neurons that allow you to see, hear, or touch, whose damage can lead to permanent loss, the nose keeps growing shiny new cells.
Despite the qualitative and quantitative differences between dog and human noses, throughout my investigation of our snoots, I heard a surprising comment from various psychophysicists and neuroscientists. The human “schnozzola,” as Stuart Firestein sometimes calls it, is “quite good,” he says. Dr. Noam Sobel, neurobiologist at the Weizmann Institute in Israel, holds nothing back: in his papers he writes, variously, that humans have a “superb” or even “astonishingly good” sense of smell.
At first, these claims are puzzling. Every walk outdoors with my dogs seems evidence to the contrary. To see them suddenly stop, turn on a dime, and hightail it back five steps to nose something invisible on the curb is to see that my nose is an inferior model (perhaps, in this case, given what might be emanating from the curb, to my great satisfaction). If my nose were “astonishingly good,” then I should, in theory, be able to experience some dogness by just remembering how to turn the thing on.
Not quite.
The neuroscientific research does indicate that, in essence, our olfactory equipment is reasonably good. What it overlooks, though, is what you and I know intuitively: how we use our noses. I knew that I was not smelling the way my dog was: she loved to loiter on invisible odor markings on every surface, in every breeze; I rarely bothered to sniff.
On the other hand, there is one convincing demonstration of the range of our noses: breakfast. How was breakfast? Did you taste it? If so, you have just confirmed your sublime sense of smell: taste is 80 percent smell. When we chew food, we are basically loosening odorant molecules from their tethers, warming them, and sending the odor-laden air backward in the mouth, where it is but a quick journey up the chimney of the throat to the nose. If in your childhood you ever experienced or witnessed the classic milk-out-the-nose result of getting the giggles in the cafeteria, you have experienced the short connection between the mouth and the nose. Smelled food needn’t go all the way out; indeed, it only has to rise to the olfactory epithelium. As we exhale while eating, air from the lungs pushes past the back of the mouth, grabs some warmed food odors, and sends them up into the nose’s backdoor. At least, if you’re being polite and chewing with your mouth closed.
This top-secret route is called retronasal olfaction. Humans are terrific back-of-the-mouth smellers. The retronasal route is largely responsible for the fact that we experience food as having any flavor at all. While the taste buds impart experience—of sweet, sour, bitter, salty, or umami—these experiences will never add up to what we mean when we think breakfast. “The sense of flavor produced is a mirage,” Gordon Shepherd, another neuroscientist, has written. “It appears to come from the mouth.” Breakfast’s deliciousness comes largely from the experience of its odor, as you can quickly confirm by plugging your nose while you take a bite. The feeling of the food—the crunch of the toast collapsing into a softness—is still all there. Indeed, the feeling of the food may be more present than you’d like: repeated chewing and toast suddenly feels gummy on the tongue, not an experience most are hoping for with their morning toast. Unplug your nose and the taste comes back in waves: a yeastiness, perhaps a caraway seed, the rich note of butter. Your nose did that!
You might experiment with an orange. Pick out a firm, well-colored specimen. A delicious, bright-smelling odor will greet you as your thumbnail punctures the rind: pith, zest, the effervescence of orange. Peel off a segment, slice it in two, and pop a half in your mouth. Let it rest on your tongue, but do not bite. You might feel its juiciness, sense that it might be sweet—but, notice, you cannot taste it. Now chew! The orange has returned to your senses. Pinch your nose and it disappears. Unpinch it and it’s back to citrus central.
The reason it tastes so pleasing may be what the neuroscientists mean when they say we have great noses.
So it is that our orthonasal (through the nostrils, breathing in) olfaction is surpassed by our retronasal (through the back, breathing out) olfaction. If you’ve ever watched a dog eat, you have seen that the conditions seem to be reversed for the dog. Though your dog may delight in rolling in dead squirrel and may lick a passing dog rump with seeming pleasure, if you put something unappetizing in his bowl, he sniffs it and turns up his nose at it. Dogs use orthonasal for examination. If, on the other hand, the food passes muster, it is usually gulped down. Chances are that there is not much or indeed any retronasal olfactory experience: airflow in the nose hinders smells from rising up the very long route from the mouth. Nor is the food even in the mouth long enough to be smelled—let alone savored.
Since the olfactory neurons reach into nose on one end and into brain on the other, a single synapse—the connection between neurons—separates the world of subway odors and over-perfumed teenagers from our fragile central processing unit. In two synapses word of odor has traveled all the way to the cortex. “One of the reasons I work on olfaction is that it’s a very shallow circuit,” Firestein told me. “You can get from the outside world to cortical tissue in the brain in two synapses—two synapses! In the visual system you’d still be in the outer retina.” The nose reaches the cortex lickety-split.
Once in, olfactory information cascades through the brain, knocking us into sensation and remembrance. This process—the creating of the olfactory experience—is not deeply understood, even in humans. Every smell researcher I talked to, though, held out hope for the answer to how the actual experience of smelling is formed. Firestein, who, like many olfactory researchers I spoke with, came to his research topic inadvertently, told me: “The promise in olfaction is that it is one of the systems in the brain where we really could get from an initial stimulus interaction”—from the odorant—“to some kind of a percept.” Such a thing is within reach of the science of vision. When we spot a parent’s face in a crowd, we now know that there are specific cells in the visual cortex that identify the vertical and horizontal lines on the face and others that recognize the fact of it being a person’s face and not a balloon face—even before it is linked to memory and we can smile and say, “Dad!” The scientific knowledge of what happens past the olfactory bulb, by contrast, is a little scantier.
What happens upstream? It is not uncommon for an academic paper on some component of olfaction to say that an interesting-looking part of the system is “unknown.” How the brain translates a pattern of neural firing into recognition of a scent is still a mystery. Even the mechanism of the very first step, the receptors, is still partly unconfirmed. “On all these different fronts we have no idea,” Vosshall tells me. “We don’t know what the odor space is, we don’t know how the receptors capture that odor space, and we have no idea how the brain takes all of this information and makes a picture.” Avery Gilbert puts it more bluntly: once you get past the bulb, “All bets are off. Nobody has a fricking clue.”
What we do know is that once we are two synapses in, many regions of the brain then hear about the smell: this includes various other parts of the cortex, the amygdala, the hippocampus, and the cerebellum. These landmarks are clues to unpacking some of our experience of smells. First, noticing and responding to a smell can feel automatic, unmediated by reflection. There is a reason for this: olfactory information goes straight to the forebrain, missing the stopover point—the thalamus—where all other sensory systems arrive when entering the brain. Without air traffic control, the scent is flying in under the radar. Our reaction to a smell is often just as fast as the noticing of the smell. Second, olfaction is the quickest route into the amygdala, considered the emotional center of the brain. “The memories you get from olfaction are always emotional memories,” Firestein confirms. “You don’t smell something and remember an equation, or a page of text. It’s always Grandmother’s house, somebody’s closet, first day of school, an ex-lover.”
Third, the hippocampus is involved: the seahorse–shaped part of the brain involved in the making of memories. Sitting in a too-large overstuffed chair in the dark of your grandmother’s living room; coming upon a decaying animal in the woods; a new boy at school scooching in next to you on the bus after gym. As we begin to process these memories, a rush of odor sneaks in on the memory’s coattails. Later, the odor itself sparks the whole scene.
Indeed, if smell has a good reputation with us, it is for its role in igniting memories long hidden from view. Scents cause a scene to shine suddenly—a sun blazing out from behind clouds, coloring the space before it. Often the memory is accessible only through the trigger of a smell: as a molecule wafts into your nose, you are transported into a childhood far, far away, and into the head of the child who inhabited that time and space. The limits of brain science on olfaction seem apt, somehow, given the limited access the conscious mind has to the memories preserved by unknown odors. These memories are not Proustian, as the term has begun to be used: they are not held in crystalline suspension, undistorted by subsequent experiences and learning. But they are evocative, calling forth, as often as not, a summary of an experience.
Ask anyone for their oldest smell memories and you get these characteristic, emotive responses.
Gene, who worked in Dad’s [furniture] shop, he was the guy who varnished and worked with the woods and he always smelled of the stuff. That was the smell of Dad, a bear of a guy. And Mom’s attic smelled like—was it mothballs? It had a strident smell . . . she was so tough on Dad.
My mother:
My grandmother would share a room with me when she visited, each of us sleeping in a twin bed. She would put this talcum powder on herself in the morning—poof poof poof—and it went everywhere. I did not like that.
The inside of Daddy’s hat. Holding it before handing it to him, hanging it up . . .
A rooftop tar warmed by summer, the smell of your grandparents’ attic, the brewery or river or tree grove on a childhood walking route, blackboard chalk and rubber cement, a struck pipe or a rolled cigarette, Play-Doh and suntan lotion, wet wool. A smell caught by an inhalation can be friction to matchstick, igniting the dormant memory. Let loose from the downy dandelion head of memories is a seemingly single soft moment with a thousand threads that spin away. Interestingly, these memories are rarely brought on by the foul and noxious odors that vex us in our ordinary days; instead, they are colored the nostalgic hue of childhood. I catch a sharp, bright smell like that of old tapes and am brought to the round, woody, tobacco smell of my father’s desk in his study, the wide drawers opening to reveal packs of cigarettes, untold sundry desk supplies, and long pads of paper decorated in his scribbled hand—and there he is, sitting before me, large and smiling, ready to pause to greet a daughter poking her head in. It is not one moment but all such moments that I see: a childhood stitched together by drafts of smells.
Do we all smell the same? The answer, you surely know if you have a functioning nose and have not been living in a cave, is clearly not. And this is true of both meanings of the question: How do we smell—is it the same? and What do we smell (or taste) of the world—is it selfsame? For the former, a trip on the subway at 8:30 on a weekday morning will serve to disabuse us of the notion that it is applied fragrances—perfumes, colognes, scented shampoos—that make us smell different from one another. If anything, fragrances unify us in smells, whereas our individual odor is unique.
And just as the philosopher might puzzle over whether we all see the same color that we call red, it is an open question whether we all smell the same odor that we call by a name—the strawberry or spice that accompanies the red. We all smell different odor scenes: exactly what you smell of the world is different from what the person standing right next to you smells. This is part biology and part autobiography. On the one hand, there is good evidence that every person’s olfactory genome is slightly different, resulting in individual variations in what odors each of us can notice and attend to. Selective anosmia—smell-blindness—to particular scents can be inherited. Some people with a particular genetic construction cannot smell isovaleric acid, a component of body odor, at all. People differ in the threshold at which they can detect the presence of various scents by several orders of magnitude.
On the other hand, we each learn odor preferences and aversions, and even cultivate degrees of attention or inattention. While we both may say we see red and smell strawberry, your red may be brighter than mine. And my strawberry may smell sweeter—and may bring to mind the intertwined smells of tomato-plant stems and warmed, pocked strawberries on the vine on a Sunday afternoon in the garden by the house. (Boy, those were delicious nuggets of berries.)
There are better or worse smellers, of course. “Many people claim they don’t have a good sense of smell—” Firestein begins, then implicates himself: “like me. I don’t have a very good sense of smell. It’s almost invariably not a neurological issue.” Instead, “it’s sinusitis, it’s inflammation, it’s allergies . . .” The conduit to the epithelium must be clear. “You can then say to them, ‘Well, how is food for you? Do you like food?’ That, they taste fine.” Flavor is intact, so retronasal smell is intact. They have a sense of smell and do not know it.
But the majority of the experienced difference between individuals in their sense of smell is within their control. Every perfumer is made, not born. Even each detection dog is trained for years before being sent out to find explosives or bedbugs or pine martens or illegally imported guava fruit.
How much are you willing to push out your nose and sniff at the world?
I. Notably, cetaceans are an exception: dolphins, for instance, do not have an olfactory bulb, though they have a “nose.”
II. It is worth noting, in this age of distinction between natural and man-made or artificial products, that the term chemicals includes it all: every product of nature is wrought of chemistry.
III. Even so, some nonhuman primates can detect smaller amounts of fruit odors called aliphatic acetic esters than dogs can. This makes sense for primate frugivores—or at least fruit lovers—as contrasted with the historically carnivorous ancestors of the dog. (Lest any primates feel too proud, know that Asian elephants are also very good with their aliphatic odorants.)
IV. With exceptions: metal does not have a smell, for instance. Just as the “smell of sun” is the smell of things warmed by the sun, not the smell of the sun, the “smell of metal”—an iron banister after touching it, a handful of pennies—is actually the smell of the metal interacting with our own sweat, not a smell of the metal per se. Indeed, the researchers who discovered this describe metal’s smell as a “type of human body odor.”
V. This is not to say that we might not implicitly detect each other’s biology in some other way: researchers are looking at “trace amine associated receptors” as perhaps involved in detecting the presence of bacteria. If they do so, then Firestein says, “The types of things that people would have said the pheromones are doing . . . judging the relative health of a potential mate or rival,” could be done by these bacteria receptors.