Upper respiratory infections are one of the most common causes of temporary, and sometimes lasting, loss of taste and smell. Doctors have recognized this connection long before COVID-19 made it headline news; the medical term “post-viral olfactory dysfunction” describes smell loss triggered by any common cold virus. What changed with the pandemic is how widespread and conspicuous the problem became, prompting a wave of research that has deepened our understanding of why viruses damage these senses and what can be done about it.
How a Respiratory Virus Disrupts Your Sense of Smell
There are two basic ways a virus can knock out your ability to smell. The first is straightforward: swelling and mucus physically block odor molecules from reaching the smell receptors high inside your nose. This is the stuffed-nose mechanism most people are familiar with from a bad cold. When the congestion clears, smell usually returns.
The second pathway is more damaging and involves the virus directly harming the cells responsible for detecting odors. Research during the pandemic revealed that SARS-CoV-2 preferentially infects sustentacular cells, the support cells that surround and maintain the olfactory sensory neurons in your nasal lining.1PubMed Central. SARS-CoV-2 infection of sustentacular cells disrupts olfactory signaling pathways When those support cells are compromised, the sensory neurons they prop up can no longer function properly, even though the neurons themselves may not be directly infected. This explains something that puzzled early COVID researchers: many patients lost their smell without much nasal congestion at all. MRI studies showed that in a significant number of these patients, the nasal passages remained clear, pointing to damage at the cellular level rather than a simple blockage.2PubMed Central. Post-viral olfactory loss and parosmia
This sensorineural damage is not unique to COVID. Post-viral olfactory dysfunction has long been recognized as a neurogenic disorder caused by common cold viruses, including rhinoviruses, parainfluenza viruses, and coronaviruses circulating before 2019.3PubMed Central. Heterogeneous Damage to the Olfactory Epithelium in Patients with Post-Viral Olfactory Dysfunction What differs between viruses is the severity and frequency with which they cause it.
Is It Really Your Taste That Is Gone, or Your Smell?
Most people who say they “can’t taste anything” during a cold are actually experiencing smell loss. That sounds counterintuitive, but the flavors you perceive when eating are mostly constructed by your brain from odor molecules that travel from the back of your mouth up into your nasal passages. The tongue itself detects only basic categories like sweet, salty, sour, bitter, and savory. Strip away the smell component, and food tastes flat and featureless even though the tongue is working fine. So when a virus impairs your olfactory system, the perceived loss of “taste” is typically a loss of retronasal smell.
COVID-19 complicated this picture. Research using home-based taste testing found that SARS-CoV-2 reduced the ability to perceive purely gustatory stimuli like plain salt and sugar solutions, stimuli that have no odor component at all.4PubMed Central. Covid-19 affects taste independently of smell: results from a combined chemosensory home test and online survey from a global cohort This confirmed that COVID could impair true taste sensation independently of smell, something less commonly documented with ordinary cold viruses. If you catch a regular cold and feel like food has lost its flavor, it is almost certainly your nose, not your tongue, that is the problem. If a COVID infection leaves food tasting wrong, genuine taste-cell damage may be part of the equation.
COVID Versus Influenza and Other Cold Viruses
Smell and taste disorders have always occurred with respiratory infections, but COVID dramatically amplified the risk. A large matched comparison found that the three-month rate of smell and taste disorders was roughly seven times higher after COVID than after influenza, with matched risk ratios around eleven to one.5PubMed. Comparison of the incidence of smell and taste disorders between influenza and COVID-19 The overall incidence was still under one percent for COVID and a tenth of a percent for flu in that dataset, but the relative difference was striking. Earlier SARS-CoV-2 variants, especially the original strain and Alpha, were particularly notorious for causing sudden, severe smell loss. Later variants like Omicron appeared to cause chemosensory problems less frequently, though they still did so more often than typical cold viruses.
From an MRI standpoint, COVID-related smell loss tended to produce less severe structural damage to olfactory regions than post-infectious olfactory dysfunction caused by other viruses, even though it was far more common.6PubMed Central. A Comparative Olfactory MRI, DTI and fMRI Study of COVID-19 Related Anosmia and Post Viral Olfactory Dysfunction In other words, a cold virus that happens to damage your smell may do so more thoroughly on a structural level, but COVID was unusual in how often it triggered the problem.
What Happens Inside Your Brain
Smell loss from a respiratory infection is not just a nose problem. The olfactory bulb, a small structure at the base of the brain that processes odor signals, can shrink measurably after a viral assault. Brain imaging of patients with persistent post-COVID smell loss found that those who still reported dysfunction had significantly smaller olfactory bulb volumes compared with patients whose smell returned to normal.7Scientific Reports. Reduced olfactory bulb volume accompanies olfactory dysfunction after mild SARS-CoV-2 infection Separate imaging work showed that over ninety percent of patients with lingering COVID-related smell loss had abnormal signal intensity in the olfactory bulbs, including scattered bright spots and signs of microhemorrhages, and about a fifth had signal changes in the primary olfactory cortex itself.8PubMed Central. Olfactory Bulb MRI and Paranasal Sinus CT Findings in Persistent COVID-19 Anosmia
These findings help explain why recovery sometimes takes months rather than days. The nose can regenerate its olfactory neurons over time, but the process depends on the olfactory bulb receiving and interpreting their signals correctly. When the bulb itself is inflamed or reduced in volume, that feedback loop is impaired. The good news is that olfactory bulb volume can recover as well, and there is evidence that targeted rehabilitation speeds this along, a topic covered below.
How Long Recovery Takes
For most people, smell and taste come back within weeks. By self-report, roughly ninety-five percent of patients recover olfactory function within six months after COVID infection.9PubMed Central. Recovery rates and long‐term olfactory dysfunction following COVID‐19 infection That number sounds encouraging, but it comes with an important caveat: when patients are tested with standardized smell kits rather than simply asked if they think their smell is normal, the rates of persistent dysfunction are higher. People tend to overestimate how well they can smell, partly because the brain adapts to its new baseline. Research in healthy older adults found that roughly three-quarters of those with measurably reduced smell sensitivity believed their sense of smell was normal.10PubMed. Unawareness of smell loss in normal aging and Alzheimer’s disease: discrepancy between self-reported and diagnosed smell sensitivity This mismatch means some people walk around with partially impaired smell after a URI and never realize it.
Recovery has been documented continuing for at least two years after infection, so patience matters.9PubMed Central. Recovery rates and long‐term olfactory dysfunction following COVID‐19 infection Some patients, however, do experience incomplete recovery. A survey-based study found a significant proportion of patients still reporting dysfunctional taste and smell well beyond the acute phase, with eleven patients retaining both impairments at follow-up.11LIAQUAT MEDICAL RESEARCH JOURNAL. Long term recovery assessment of post-COVID-19 loss of taste and smell- A population-based survey
Who Is More Likely to Lose Smell, and Who Takes Longer to Recover
The risk of developing smell loss after a respiratory infection is not evenly distributed. A case-control study found that women were more likely than men to develop olfactory dysfunction after COVID, and younger patients were more likely to notice it than older patients (though older patients who lost smell had a harder time getting it back).12PubMed Central. Unmasking Risk Factors for Post-COVID-19 Olfactory Dysfunction Resulting From Early Stages of the Pandemic: A Case-Control Study of Lost and Lingering Smells Patients with seasonal allergies had about a forty-four percent higher likelihood of developing the problem, and those who were hospitalized for their infection were at increased risk as well. For chronic smell loss specifically, being female, older, non-White, hospitalized, or having cerebrovascular disease were all associated with worse outcomes.12PubMed Central. Unmasking Risk Factors for Post-COVID-19 Olfactory Dysfunction Resulting From Early Stages of the Pandemic: A Case-Control Study of Lost and Lingering Smells
There may also be an anatomical component. One study found that a longer olfactory cleft, the narrow channel at the top of the nose where odor receptors live, was associated with a substantially higher risk of persistent smell loss after COVID. The odds of lasting dysfunction were about seven times higher when the olfactory cleft exceeded forty millimeters in length.13PubMed Central. Olfactory Cleft Length: A Possible Risk Factor for Persistent Post-COVID-19 Olfactory Dysfunction You cannot measure your own olfactory cleft at home, but this finding hints that individual anatomy contributes to why some people recover quickly and others do not.
Parosmia and Phantosmia
Not everyone who has smell trouble after an infection experiences simple loss. Many patients develop parosmia, where familiar odors are distorted and typically perceived as foul. Coffee smells like sewage, onions smell like rotting meat, and perfume becomes nauseating. Parosmia often appears as the brain begins to recover and rewire its olfactory pathways, which is why it sometimes shows up weeks or months after the initial loss rather than at the same time. It is generally interpreted as a sign that neurons are regenerating, albeit imperfectly.
Phantosmia is rarer and involves smelling things that are not there, such as a persistent smell of smoke or chemicals without any source. Both parosmia and phantosmia can be deeply distressing, but they tend to improve gradually over time. One study of patients treated with a short course of systemic corticosteroids found that about eighteen percent of those with parosmia and roughly twenty-eight percent of those with phantosmia reported improvement after treatment.14American Journal of Otolaryngology. Immediate impact of a short course of systemic corticosteroid on olfactory dysfunction, parosmia, and phantosmia
Olfactory Training
The most consistently supported rehabilitation approach for post-viral smell loss is olfactory training, a structured daily routine of sniffing specific scents. The classic protocol uses four odors representing different scent categories, typically rose, eucalyptus, lemon, and cloves. You sniff each one deliberately for ten to fifteen seconds, twice a day, while trying to recall what the scent should smell like.
A systematic review of the evidence found that olfactory improvement from training exceeded the natural course of recovery, and that patients benefited more from longer training periods, ideally beyond twelve weeks. Both standard and modified training protocols (rotating different odorants, varying concentrations) appeared to increase effectiveness, with peak therapeutic gains typically occurring around six to nine months of training.15PubMed Central. Steroids and Olfactory Training for Postviral Olfactory Dysfunction: A Systematic Review Notably, olfactory training does not just improve subjective smell performance. A prospective study found that patients who underwent training showed significant increases in olfactory bulb volume, suggesting that the exercise physically helps the brain’s smell-processing structures recover.16PubMed. Association of olfactory training with olfactory bulb morphology in adults with post-viral long-lasting olfactory dysfunction: A COVID-19 related prospective study
The appeal of olfactory training is that it is free, carries no side effects, and can be done at home with materials you likely already own. Its limitation is that it requires patience and consistency over months.
Medical Treatments Under Investigation
Beyond olfactory training, several medical approaches have shown promise, though the evidence base is still developing. Topical corticosteroids, usually nasal sprays containing budesonide or mometasone, are the most commonly prescribed medication. A short course of about three months has shown favorable outcomes for post-viral olfactory dysfunction and is generally well tolerated.17CMAJ. Postviral olfactory dysfunction Systemic (oral) corticosteroids have more mixed evidence. One study found that roughly a quarter of patients experienced meaningful smell improvement after a short course, compared with about ten percent in a control group.14American Journal of Otolaryngology. Immediate impact of a short course of systemic corticosteroid on olfactory dysfunction, parosmia, and phantosmia Patients with worse function at the start tended to show greater recovery, suggesting that steroids may help most when inflammation is still active.
An emerging and intriguing option is intranasal insulin. A systematic review found that insulin delivered into the nose was generally associated with improved smell scores, with delivery via absorbable materials (a dissolvable film placed in the nose) performing better than self-administered sprays.18PubMed Central. The Efficacy of Intranasal Insulin in the Treatment of Post-Viral Persistent Olfactory Dysfunction: A Systematic Review Combining intranasal insulin with budesonide appeared to produce better results than either alone.19PubMed Central. Comparison Between Intranasal Insulin Films Alone and Combined Intranasal Insulin Plus Steroid Films for Post Viral Olfactory Dysfunction This is still an experimental approach, not available at most clinics, but it represents one of the more promising leads in the field.
When Smell Loss Becomes a Safety and Mental Health Issue
Losing your sense of smell is easy to dismiss as a minor annoyance, but the consequences can be serious. Your nose is a first-line warning system for smoke, gas leaks, spoiled food, and chemical hazards. Without it, you may not detect a fire until you see flames or notice a gas leak until you feel symptoms. Your sense of taste, similarly, helps you avoid ingesting something toxic or spoiled. When both are impaired, everyday safety decisions become harder.
The psychological effects can run equally deep. A systematic review found that between forty and seventy-six percent of patients with olfactory dysfunction from various causes experienced depressive episodes during the course of their condition.20PubMed Central. COVID-19 loss of taste and smell: potential psychological repercussions Loss of smell strips the pleasure from cooking and eating, which in turn erodes appetite and social engagement. People who cannot smell themselves become anxious about body odor, sometimes showering excessively. Those who cannot taste properly tend to add more salt and sugar to compensate, raising the risk of cardiovascular and metabolic problems over time.20PubMed Central. COVID-19 loss of taste and smell: potential psychological repercussions A 2025 review described the impact of olfactory loss on quality of life as moderate on average, but severe for a subset of patients, permeating nutrition, social well-being, and sense of personal safety.21PubMed Central. The impact of olfactory loss on quality of life: a 2025 review
Children and Adults
Children can lose their sense of smell after a viral infection too, though they report it less often, possibly because younger kids have difficulty recognizing or articulating the change. A hospital-based study comparing children and adults with post-COVID chemosensory disorders found that the two groups were broadly similar in the patterns of smell and taste loss they experienced. No significant differences emerged based on gender within either group, and the types of disorders were largely the same. The one measurable difference was that children were less likely to report loss of nasal trigeminal sensation, the “burn” or “cool” feeling from substances like menthol or chili.22PubMed Central. Evaluation of children and adults with post-COVID-19 persistent smell, taste and trigeminal chemosensory disorders: A hospital based study In practical terms, if your child complains that food tastes weird after a cold or flu, the same mechanisms are at play as in adults, and the same patience applies to recovery.
How to Tell If Your Smell Is Actually Impaired
If you suspect your smell has not fully returned after a respiratory infection, trusting your own judgment may not be enough. As noted earlier, many people with measurable smell loss believe their sense of smell is normal. Formal testing with validated scratch-and-sniff kits or standardized odor identification tests remains the gold standard. Researchers have also developed at-home screening tools: one such test asks you to rate seven common household scents, and while it showed moderate accuracy at identifying those with complete smell loss, it missed a meaningful fraction of milder cases.23JAMA Otolaryngology–Head & Neck Surgery. Development and Validation of a Novel At-home Smell Assessment
If you want a rough check at home, try smelling items with distinctive odors you know well: ground coffee, peanut butter, cinnamon, vanilla extract. Test each nostril separately by holding the other closed. If you detect nothing from one or both sides, or if familiar smells seem wrong, it is worth mentioning to your doctor. For persistent problems lasting more than a few weeks, a referral to an ear-nose-and-throat specialist can provide formal testing and guide you toward olfactory training or medical treatments that may help.