Nine years ago, on an April morning in San Francisco, I awoke to a concussion that seemed to silence everything around me. I noticed half-painted canvases lying haphazardly around the room; I ran my fingers along an eggshell-white wall punctuated with slivers of light filtering through half-shuttered windows. Yet I felt strangely disconnected from my environment. There was something that hung like a veil over my perception.

It was first apparent that something was wrong when I took a bite of a falafel sandwich that morning and it hung like tasteless cardboard in my mouth. Later that morning, I drove through rush-hour traffic on the smoggy highway that cuts through the valley between San Francisco and Sacramento, unmoved by the exhaust that was streaming in through my open window. At the time I worked at a fondue restaurant where the odors of melted cheese and broth were particularly strong. Some days they made me want to gag, and some days they made me hungry, but they were always there, permeating my clothes and hair long after they were washed. For some reason, I didn’t notice them that day. I thought it had something to do with the fog of my concussion, but when I went back to the kitchen to dump out a pot of broth from one of my tables, it was then that I realized: I couldn’t smell.

My concussion came after a day of trespassing to take photos in a Bayview-Hunters Point graffiti yard with a college friend. Afterward we went to a bar, where after a single beer and a puff of medical marijuana, I stood up to use the bathroom and awoke to EMTs hovering over me as I lay confused on the floor. They told me I’d passed out cold, and promptly transported me to a hospital by ambulance where I was given a dismissive diagnosis of a mild concussion. “You're in the Tenderloin—we see this all the time,” the attending ER physician told me, before sending me home to be watched by my friend overnight. Other than the bruise to my head, I thought I was okay when I drove home to work the next morning.

Later my general practitioner would order a string of tests—an EEG with forced hyperventilation and strobes to test for epilepsy, a fasting blood-glucose test, and an MRI to look for potential brain and skull injury—all in an attempt to identify why I passed out. He told me my blood tests showed I’m hypoglycemic, and the low blood sugar could have caused me to pass out. But when I asked about my inability to smell, he shrugged off the thing he couldn’t see, the ailment invisible to everyone but me.

The months after the accident were a blur. My first reaction to my loss of smell was curiosity and awe. What a strange thing to suddenly be stripped from one of the antennas I had to the world. Since around 75 percent of the flavor we detect in food comes from the sense of smell, bacon just didn’t do it for me anymore. So I committed to vegetarianism. I stopped wearing perfume, which suddenly seemed a vacuous luxury. But I also began to feel new insecurities about my own scent and the smells in my environment, and I began to dissociate from certain aspects of my life.

My sense of smell was once so keen it would turn me off from certain people and places. In a city, it’s surreal not to smell the putrid decay of garbage bags piled high on the street, not to be romanced by fresh-baked pastries in the wee hours of the morning. Right after the accident, I remember driving to my parents’ house, distraught, crying uncontrollably. I felt cut off from the world around me, trapped inside a body that wasn’t functioning properly. The world seemed flat and dull, as if drained of color. I didn’t want to live without a sense-and-a-half. And, I realized, this loss meant there were suddenly new and unexpected ways my life could end—by gas leak, by fire, or from spoiled food.

Lindsay Comstock

Despite the various ways smell protects us, humans often count it as one of the senses they could do without. (In a recent study by McCann Worldgroup, “53 percent of those aged 16-22 and 48 percent of those aged 23-30 would give up their own sense of smell if it meant they could keep an item of technology.”) For me, too, it was a sense I thought I could do without—until I lost it.

The more I researched anosmia—the medical term for my condition—the more questions I had. Smell is strongly tied to memory, so did this mean that the memories I would make as an anosmic would be more difficult to recall years later? Would I ever fall in love again if I couldn't physically smell another’s scent, the chemicals intimately communicated by the human body? Would I have trouble bonding with my own child one day? Would I lose my connection to myself if I no longer was acquainted with my own body odor? And why did a minor concussion entirely knock out my ability to smell?

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My own research suggests that likely my loss of smell was caused by my brain bouncing against the front of my skull when it hit the ground, severing some 400 hair-like olfactory receptors that bind to odor molecules at the back of the nasal cavity, which pass through a honeycomb-like cribriform plate, and carry signals to the olfactory bulb in the brain. When the nerves are damaged, they are no longer able to send signals to the olfactory bulb, which connects to the amygdala, interpreting and mapping up to one trillion different odors.

Most sensory research focuses on visual and auditory disorders because those senses have the biggest implications for people’s ability to survive and thrive. People can live without their sense of smell, so there have been fewer resources devoted to research on the topic. But according to researchers at the Monell Center in Philadelphia, more than 6.3 million Americans are living without their sense of smell. Founded in 1968 as a center for taste and smell research, the institution is attempting to learn more about this sense and its relation to quality of life. In early 2014, the center began A Sense of Hope—a three-year awareness and research campaign for anosmia.

When I visited the center recently, I learned why I’ve been depressed lately. According to Pamela Dalton, an experimental psychologist at Monell, the direct connection between olfactory receptors and the amygdala creates a feedback loop in the brain when you smell something. If odor input to the brain ceases, behavioral or emotional changes might occur. “In animal studies where [researchers] have ablated the [animal’s] sense of smell, they do see behavioral changes,” she says. “The [animals] seem to have certain neurotransmitters reduced in the circulation of their bloodstream, which may be associated with a certain blunted emotional state.” When I describe my olfactory condition, she offers, “[It’s like] you’re getting the broad brush strokes but not all of the detail, right?” This is exactly it, I think.

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Growing up in the suburbs of Sacramento, one of the smells I do remember is that of freshly cut grass in the summertime. Its scent signaled freedom because it was the sweetest and most verdant right around the time school let out for summer vacation. In summer, the smell of chlorine became my eau-de-toilette. My sister and I learned how to swim at our next door neighbor’s house, and while we were in the pool, the smell of homemade potato pancakes wafted from their kitchen window, luring us inside.

I also distinctly remember those fall days the rice fields were burned in the lowest recesses of valley in Sacramento County. The brown smog hung thick in the air, burning my eyes. An acrid odor held on, nestling in my hair, hinting at the sickening smell of too much caramel corn at the state fair.

Because the olfactory system depends on the turnover of the cells that interact directly with the environment on a daily basis, the nerves have the capacity to regenerate. But it’s unclear to scientists why this occurs in some people with anosmia and not in others. I was told by my doctor there wasn’t anything I could do besides wait, and give my brain time to heal, or see an ear, nose, and throat specialist. My research told me there weren't any medical treatments currently available for nerve damage, and I didn’t want to waste my time with pointless examinations of my sinuses. So in desperation, I tried anything and everything. I took mushroom supplements that claimed they would boost brain function. During meditation, I visualized the nerves regenerating, like roots of trees inching their way backward to the olfactory bulb from which they were severed. I went to several acupuncture sessions. I’ve tried craniosacral therapy.

In the absence of smell, I became more aware of my other senses. I cooked with my eyes—making dishes with attention to color and texture and the balance of tastes I could still sense with my tongue. During my last year of college, I immersed myself in photography.

Lindsay Comstock

In my case, for reasons that are unclear, my sense of smell began to recover after those first few months. I first noticed more pungent fumes, like smoke and onions, and slowly detected other scents—a surprising whiff of jasmine or rose or coffee or sewage or body odor. After the horror of not being able to smell at all, every scent was a welcoming symbol of life, and of my own returning vitality.

But in the years since the accident, scent hasn’t been reliable. In the first year, I experienced bouts of parosmia and phantosmia, phenomena that can occur after nerve damage to the brain, where a smell is misinterpreted as something else. One time, while walking on a street in San Francisco, I confused the smell of baking bread with sweaty feet. Some days scents aren’t present at all; other days they are dim and incoherent. Sometimes the smell of spiced meat and burnt oil from a food cart on the street assaults me with a jarring intensity, but it only lasts for an afternoon. Almost a decade later, I function close to the level of someone with a normal sense of smell, but I rarely have the experience of an aroma conjuring up a memory long-buried and dusty.

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Despite all the hype about pheromones, I learned from Dalton at the Monell Center that there is no evidence that humans have a functional vomeronasal system for pheromone detection as most mammals do. Rather, “People are attracted to each other based on different major histocompatibility complexes that promote different immune responses,” she explains. In addition, people can still pick up on social and chemical cues through scent, “which can be generated by an internal metabolic state or emotional state that affects gland secretions. Emotional state can be sensed through smell,” says Dalton.

She goes on, confirming my suspicions that I had been experiencing a barrier in my relation to the world. “If it is truly all olfactory-mediated you’re missing out on the whole social-chemical signal world, or much of it, if you’ve lost your sense of smell. So that would suggest you would be less perceptive about people’s emotional states. Your interaction with others would be somewhat disrupted, or at least it wouldn’t be as accurate. But we just don’t know. The studies haven’t been done on anosmics.”

What scientists do know is that the sense of smell is a “plastic system,” according to Beverly Cowart, a sensory psychologist at Monell—and one that is learned. There are certain odors, like wintergreen, which can have different associations for different cultures. “It’s [a smell] that’s usually pleasant to Americans, but in England, it’s associated with the dentist,” she says with a laugh.

Monell is currently working on using stem cells from healthy nasal tissue to try to regenerate olfactory nerves in people with smell disorders either caused by loss of nasal tissue or damage from chemotherapy. So far, they’ve been able to regrow nerve cells from stem cells in the lab and they’ve seen these new cells activate with the input of odor molecules. But they’re a long way off from determining how these nerves will connect to the brain.

One area that they are seeing results in, however, is focused smell training. By consciously smelling and identifying things in one’s environment, synaptic connections appear to be strengthened. “There’s evidence that stimulation of the olfactory system [through odor exposure] can enhance receptor expression and possibly even stimulate regrowth,” Cowart says.

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Lindsay Comstock

Sometimes when I’m back near San Francisco, visiting Marin County where my grandparents lived, winding through narrow redwood-forest roads on Highway 1, I can almost smell the foggy eucalyptus exhalation filling the breeze. My partner grew up in the area, smelling these same smells, painting these same scenes, where clouds would wave from puddles of brackish wetland water along Richardson Bay. When I met him years after the accident, in Brooklyn, I always joked that I could smell the California sunshine in his New York affect.

Truth is, I don’t know if I could identify his shirt by smell alone. I rarely detect the scent of the ozone right before it rains. Rooms are often a blank space—the minutiae of residual odors that signal the texture of history are lost on me. And I’m not often stricken with disgust at foul odors anymore. Some say I’m luckier for it. But often I wonder what I’m missing out on in the world.