During a typical annual physical, a patient is likely to get checked for any deviations that might affect their senses of sight, hearing, and proprioception. However, while a doctor will usually look up the nose, searching for inflammation or discoloration, she likely won’t test—or even ask about—your sense of smell.
This omission may seem unremarkable to many readers. The average person tends to view olfaction as our least important sense, especially when it comes to our ability to navigate and function in the world. Even at the height of the COVID-19 pandemic, when smell loss and its effects were a particularly hot topic, researchers found that survey respondents put far less value on olfaction than they did on vision, hearing, or even material goods. A quarter of college-age subjects said they’d sooner part with their sense of smell than their cell phones.
But smell isn’t incidental, it’s just underappreciated by the general public and understudied by most modern researchers relative to our other senses. Over the last few decades, the handful of researchers and clinicians who actually grapple with this sense and what happens when it malfunctions have shown that it plays a major role in our ability to detect environmental hazards and enjoy the good things in life, like the aroma of garlic sautéing in olive oil or the unique perfume that seems to emanate from the head of a healthy baby. They’ve also found strong associations between a loss of smell and a laundry list of health conditions, including major neurodegenerative disorders.
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Many of these experts believe smell is so important and potentially indicative of health problems that we should test it as often as we do sight or vision. Valentina Parma of the Monell Chemical Senses Center, one of the few dedicated smell and taste research institutes, argued in an interview with JSTOR Daily that we ought to get our olfaction checked at every health screening “as routinely as blood pressure assessments.”
Advocates for regular olfaction testing have coalesced and their efforts have gained momentum in recent years. But while they make a strong case for adding a new diagnostic component to checkups, even the strongest smell screening proponents acknowledge they’ll need to break through popular skepticism and practical roadblocks before that goal becomes a reality.
Smell loss is usually—and intuitively—associated with colds and other respiratory tract infections, allergies, or exposure to toxicants like tobacco and alcohol, nasal polyps, and deviated septums; that is, it’s linked to anything that messes with the pathway between an airborne odor molecule, a smell receptor, and the brain. Head trauma, nerve damage, strokes, or other complications that impede the brain’s ability to translate raw data into an experience may also alter our sense of smell. Ditto for certain medications, hormonal imbalances, and nutritional deficits, which muck with wide-ranging body systems.
However, over the last couple of decades, researchers have started to notice that smell loss isn’t just associated with certain neurologic disorders—it seems to be a telltale, early symptom of them. In many people later diagnosed with Alzheimer’s, multiple sclerosis, or Parkinson’s, loss of their sense of smell preceded their disorders’ more recognizable and expansive symptoms, like motion or cognition issues, by several years. The going theory is that, as these degenerative conditions spread through the brain, they often hit smell processing sites before they affect motor or speech centers.
“Other illnesses can mimic Parkinson’s” hallmarks like tremors, explained Julien Wen Hsieh, a physician-scientist at the Geneva University Hospitals who specializes in rhinology and olfaction, in an interview with JSTOR Daily. “But they do not influence smell.”
Yet while around twenty-two percent of people live with at least partial smell loss (hyposmia) and at least three percent live with total smell loss (anosmia), most people are remarkably bad at noticing a change in the sense, especially a gradual decline.
“People are often unaware until it’s gone,” said Carl Philpott, a professor at the University of East Anglia who studies olfaction and serves as co-chair and director of research for the British smell loss charity SmellTaste, in an interview with JSTOR Daily.
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People are also bad at judging how well they used to be able to smell and, thus, how much of the sense they’ve lost. And the average clinician, for lack of education and experience, is bad at catching and responding to signs of loss, and the deeper issues it may point to, says Parma.
So, while scattered voices had long called for better smell testing, Parma explained, “systemic calls for routine olfactory screening emerged more visibly in the 2000s,” as research on smell loss’s potential role as an early warning sign of serious neurodegenerative disorders increased.
Smell loss is hardly a smoking gun. Most people with hyposmia “won’t have dementia or Parkinson’s,” stressed Michigan State professor Honglei Chen, who studies olfaction as it relates to various aging-related oucomes including neurodegenerative disorders, during an interview with JSTOR Daily. But as with other general health metrics, like blood pressure, a clinician could use an ongoing measure of olfactory function alongside other patient information or demographic risk factors as a low-cost signal to investigate further. Ideally, providers could catch and start treating neurodegenerative conditions far earlier than usual, Parma explained. And even if a patient’s smell loss isn’t related to a larger, more threatening condition, clinicians still might catch and treat clinically-relevant issues like low-symptom respiratory infections or exposure to environmental pollutants, that they may have otherwise missed.
Across the late 2010s, the push for routine smell testing started to draw mainstream interest, as the link between hyposmia and Alzheimer’s and Parkinson’s especially grew stronger. High-profile studies also suggested that a loss of smell might also be a warning sign of imminent and severe declines in function in older people; doctors could use their findings on loss of smell in this population to preempt the effects of frailty. (Those studies focused on screening older, already at-risk patients rather than the general populace.)
Interest in widespread smell screening truly took off in mid-2020, as the world realized that smell loss was one of the most common and unique symptoms of the first waves of COVID-19. (Some of the later strains didn’t compromise patients’ sense of smell.) Suddenly, public health agencies threw their weight behind developing low-cost, quick, and easy smell tests for use in-clinic or at home, as a means of screening wide swathes of the population for potential COVID-19 cases. Support for these sorts of tests faded as swabs and spit strips became more accessible. However, popular concerns about long-term smell loss following a case of COVID created an unprecedented, sustained wave of support for and awareness of olfaction research overall.
“We’ve been working quite hard to capitalize on that interest and awareness generated by the pandemic to ensure it isn’t just forgotten,” said Duncan Boak, who lost his sense of smell in 2005 following a head injury and now serves as the head of SmellTaste, in an interview with JSTOR Daily.
Granted, most of that sustained popular interest is focused on potential treatments for smell loss. But groups like Monell, which developed a test in 2020, began actively promoting the concept of universal smell screening as a rapid, accessible way to measure the presence of smell dysfunction linked to respiratory infections, as well as other pathologies.
Smell is a complex sense. Most of the scents we detect are the result of several odor molecules binding to separate olfactory receptors in your nasal cavity, sometimes only triggering sensation after hitting a threshold. Change the concentration of one molecule relative to the others—or the nose’s ability to pick up on a piece of the whole—and you’ll end up with a different olfactory experience.
As someone who’s lived with progressive smell loss for over a decade, I find that people often, when trying to understand what my life is like, assume the condition must be akin to a dimmer switch, reducing my ability to detect everything equally. It’s more like someone’s going into my brain and scrambling a massive, finely tuned mixing board, rendering me fully incapable of smelling some odors, dampening others, while leaving a few untouched. While some of those remaining scents smell as strong to me as they used to, their quality is different. Take cleaning products as an example: I’ve lost the ability to detect the pleasant additives manufacturers put into them, and now experience only a vague yet powerful chemical astringency. I’ve also lost the ability to distinguish between once-distinct aromas, like fruits, as I can now only pick up on a faint, common sweet note. And smell researchers, including Alan Hirsch, neurological director of the Smell & Taste Treatment and Research Foundation, and G. Neil Martin of Regent’s University in London, have told me in interviews for prior articles I’ve authored on olfaction that all of us are probably born with slightly different olfactory abilities. That initial capability, they added, likely changes over time—even before smell loss comes into the picture—as our noses and nerves attune to the most important odors in our cultures, environments, or personal lives.
All of which makes the process of developing an ideal smell test incredibly challenging. You can’t just wave one odor under everyone’s nose, figure out how much of it each person can detect, and assign a single absolute score like a blood pressure stat. The best tests researchers have developed use a small but diverse array of scents, presented at different concentrations and distances, to get a sense of what a patient can pick up on, when, and which they can confidently identify or distinguish from each other. But those tests “require a lot of time, effort, and human resources” to administer, said Hsieh.
Most health systems—insurance billing codes, electronic health records, and even the basic setup of an exam room—aren’t designed to account for and provide smell tests either. “We’re talking about enacting a process of fairly significant societal change,” acknowledged Boak.
And even these gold-standard exams are apt to miss things, explained Chrissi Kelly in an interview with JSTOR Daily. Kelly lost her sense of smell after a viral infection in 2012, starting a long journey of research and recovery and eventually founding the education and advocacy group AbScent. You might be able to identify a scent, but suffer from parosmia, a (usually unpleasant) distortion in what it actually smells like to you versus others, or from phantosmia, sporadic olfactory hallucinations. Neither of those conditions will necessarily register on even a complex, well-designed smell screening test.
Some advocates of expanded testing, like Hsieh, also acknowledge that the case for the utility of smell screening isn’t ironclad. Sure, maybe you can launch a few early interventions if you catch a neurodegenerative disease early. But he harbors doubts about the value of regular testing outside of populations already at risk for those conditions.
“It may introduce anxiety for patients with a declining sense of smell, which will not benefit them,” Hsieh explained. “This would do more harm than good.”
So, while Parma claimed specialists are increasingly aligned around and pushing hard for a new era of routine smell testing, it makes sense that generalist clinicians remain skeptical.
“We have a lot to do to provide more concrete scientific evidence to prove the value of this,” said Chen.
Honestly, you may not need a perfect test—a granular snapshot of a person’s olfactory abilities—to deliver meaningful benefits. Monell and other organizations have developed kits that cost about a dollar and take less than a minute to administer, which can establish an individual’s baseline ability to detect several strong and unique scents, like bubblegum and coffee, and then monitor any change in their personal olfactory abilities and experiences over time.
Even an imperfect, broad sense of change, when combined with the other rough metrics a provider tracks, may offer clues about undetected illnesses or lurking issues, Parma stressed. And catching any form of smell loss would allow doctors to help patients deal with the effects of the change itself, argued Dr. Steven Munger, Co-director of the University of Virginia Center for Smell and Taste Disorders, in an interview with JSTOR Daily.
Whether short-term or permanent, and no matter the extent or cause, smell loss exposes us to dangers we don’t necessarily recognize, like eating spoiled food or going about our business while gas leaks into our homes. It changes our relationship with food, diminishing appetites for lack of enjoyment or leading us to consume more fats and sugars just to get some kick of sensation from that pure taste. (Most of the flavor of a meal, beyond core components like sour, salty, or umami, actually comes from the odors carried up the back of our throats to our nasal passageways and the olfactory receptors therein.) And it dampens our overall experience—our enjoyment—of all sorts of everyday activities, fueling elevated levels of confusion, depression, and often isolation.
Rather than cause anxiety, a cheap, lo-fi smell test may also reassure people who’re recovering from (hopefully) temporary smell loss, inasmuch as it could give them the knowledge that they’re getting better. Even these limited benefits are surely worth an extra buck and minute per checkup, testing boosters argue. And the value of smell tests will likely increase with time and research.
In 2023, a group of smell specialists and smell loss advocates, including Boak, Munger, and Parma, gathered the largest collection of stakeholders ever for a landmark conference on the topic. There, they affirmed their joint belief in the value of smell testing, and developed a roadmap for creating testing standards, overcoming bureaucratic hurdles related to insurance coverage, and educating non-specialists on the merits of basic smell testing.
“The meeting marked a shift from advocacy to implementation planning,” Parma explained in our interview. “What remains is to operationalize this momentum into policy change, economic models, and clinical infrastructure that can support scalable, routine testing across health systems.”
“There’s still a long way to go,” Boak admitted. “But we’ll get there.”
