The most common reason for a poor sense of smell is inflammation inside the nose. Swelling from allergies, sinus infections, or a lingering cold can physically block odor molecules from reaching the smell receptors high up in your nasal cavity. But inflammation is just one possibility on a long list that includes medications, nutritional gaps, aging, and occasionally something more serious. About 4% of adults in their 40s have some form of smell impairment, rising to 25% of people in their 70s and 39% of those over 80.
How Your Sense of Smell Works
To understand what can go wrong, it helps to know the basics. When you breathe in, odor molecules travel to a small patch of tissue called the olfactory epithelium, tucked high inside each nostril. Specialized nerve cells there detect the molecules and send signals through the olfactory bulb to your brain, which interprets them as specific smells. A problem anywhere along that chain, from a stuffy nose blocking the molecules to nerve damage disrupting the signal, can weaken or warp your sense of smell.
Doctors use a few terms to describe what’s happening. A reduced ability to detect odors is called hyposmia. A complete loss is anosmia. If familiar smells seem distorted (coffee suddenly smells rotten, for example), that’s parosmia. And if you smell something that isn’t there at all, it’s phantosmia. Knowing which pattern fits your experience can help pinpoint the cause.
Nasal Inflammation and Congestion
This is the single most frequent culprit. Anything that swells the tissue inside your nose can block odor molecules from physically reaching the smell receptors. Seasonal allergies, a cold, the flu, a sinus infection, or COVID-19 can all do it. In most of these cases, smell returns once the inflammation clears.
Chronic rhinosinusitis, a condition where the sinuses stay inflamed for months, causes a more stubborn form of smell loss. The ongoing inflammation, especially when driven by a specific type of immune response involving eosinophils (a kind of white blood cell), doesn’t just block airflow. It actively damages the smell-detecting nerve cells in the lining of the nose, causing them to degenerate. Nasal polyps, the soft growths that often accompany chronic sinusitis, make it worse by adding a physical obstruction on top of the chemical damage.
A deviated septum can contribute too. If the wall between your nostrils is significantly crooked, airflow to the olfactory region on one or both sides may be reduced enough to dull your sense of smell.
Viral Infections and COVID-19
Viruses can damage smell through several mechanisms, not just congestion. With COVID-19 in particular, the virus targets supporting cells in the olfactory lining rather than the smell neurons themselves. These support cells maintain the environment the neurons need to function. When they’re damaged, the neurons can’t do their job even though they’re technically intact. This is why many people with COVID lost their smell without ever feeling particularly congested.
In most cases, the support cells regenerate and smell returns within weeks to a few months. But in some people, the damage extends deeper, reaching the smell neurons or even the olfactory bulb in the brain. That can lead to longer-lasting or permanent loss. It also explains parosmia, the strange smell distortions many people report during recovery: new neurons are growing back and reconnecting, but not always to the right targets at first.
Medications That Dull Smell
Smell and taste disturbances are associated with almost every major category of medication, with cardiovascular drugs (blood pressure medications, cholesterol-lowering drugs) among the most frequently reported. The more prescription medications a person takes, the greater the cumulative effect on smell and taste. If your sense of smell declined around the time you started a new medication, that timing is worth noting and mentioning to your prescriber. In many cases, the effect reverses when the drug is stopped or switched.
Nutritional Deficiencies
Zinc plays a specific role in smell. One of the key enzymes your olfactory system depends on, carbonic anhydrase, requires zinc to function. When zinc levels are low, that enzyme can’t do its job, and smell suffers. Zinc deficiency is a well-established cause of both smell and taste loss. People at higher risk include older adults, vegetarians, those with digestive conditions that impair absorption, and heavy alcohol users.
Ironically, too much zinc applied directly to the nose can also destroy smell. Some over-the-counter zinc nasal sprays have been linked to permanent anosmia, which is why several were pulled from the market. Oral zinc supplements at recommended doses don’t carry this risk, but megadosing isn’t helpful either. General malnutrition from any cause can also impair smell, since the olfactory neurons turn over regularly and need adequate nutrition to regenerate.
Age-Related Decline
Your sense of smell naturally weakens with age in a process called presbyosmia. Unlike sudden smell loss from an infection, this happens so gradually most people don’t notice it for years. The olfactory bulb loses roughly 10% of its key signal-processing cells each decade, so by the ninth or tenth decade of life, fewer than 30% of those cells remain. At the same time, the stem cells that replenish the smell-detecting lining of the nose become less effective, partly because of chronic low-grade inflammation that accumulates with aging.
The practical consequences go beyond missing pleasant scents. Older adults with reduced smell may not detect spoiled food, gas leaks, or smoke. They also tend to eat less or add excessive salt and sugar to compensate for food tasting bland, which can affect nutrition and chronic disease management.
Neurological Conditions
A declining sense of smell can occasionally be an early signal of a neurological condition, most notably Parkinson’s disease. Between 75% and 90% of Parkinson’s patients report a diminishing sense of smell, and the striking finding is that this symptom often appears up to 10 years before the tremors, stiffness, and other motor symptoms that lead to a diagnosis. Researchers at Yale have identified biological changes in the olfactory system specific to Parkinson’s and see smell testing as a potential tool for much earlier detection.
Alzheimer’s disease and multiple sclerosis are also linked to smell loss, though the pattern differs. In Alzheimer’s, the ability to identify and name odors tends to decline before the ability to detect them does, reflecting the cognitive component of smell processing. This doesn’t mean a poor sense of smell predicts dementia. Most people with reduced smell have one of the far more common causes listed above. But if smell loss is accompanied by memory changes, coordination problems, or other neurological symptoms, it’s worth a thorough evaluation.
Other Medical Causes
Several less obvious conditions can affect smell. Hormonal imbalances, including thyroid disorders, sometimes alter olfactory function. Type 1 diabetes has been associated with reduced smell. Even severe dental problems like extensive tooth decay or advanced gum disease can contribute, likely because of chronic infection and inflammation so close to the nasal passages.
How Smell Loss Is Evaluated
If your reduced sense of smell doesn’t resolve on its own within a few weeks, a doctor can evaluate it with a combination of a physical exam of the ears, nose, and throat, a review of your health history (including chemical exposures and head injuries), and a formal smell test. The most common version uses a booklet of scratch-and-sniff pages, each containing tiny beads filled with a specific odor. You scratch, sniff, and try to identify the smell. Incorrect answers or an inability to detect the odor at all helps quantify the degree of loss.
Another type of test measures the faintest concentration of an odor you can detect, which helps distinguish between a problem with detection (the nose) versus identification (the brain’s processing). Imaging may be ordered if a structural problem like polyps is suspected or if there are neurological concerns.
What Improves Smell
Treatment depends entirely on the cause. Inflammation-driven smell loss often responds to nasal corticosteroid sprays or, in the case of severe polyps, surgery to open up the nasal passages. Treating underlying allergies or sinus infections can restore smell within weeks. If a medication is responsible, switching to an alternative frequently brings smell back.
For post-viral smell loss, including long-lasting cases after COVID, smell training is the most supported approach. You deliberately sniff four distinct strong scents (commonly rose, lemon, clove, and eucalyptus) for about 20 seconds each, twice a day, for at least three months. The practice is thought to stimulate regeneration and proper reconnection of olfactory neurons. Studies show meaningful improvement in a significant portion of people who stick with it, though recovery can take six months or longer.
Correcting a zinc deficiency through diet or supplementation can restore smell when low zinc is the underlying issue. Foods rich in zinc include red meat, shellfish (especially oysters), chickpeas, and pumpkin seeds. For age-related decline, there is no way to fully reverse the process, but staying on top of treatable factors like allergies, medications, and nutritional gaps can prevent the loss from being worse than it needs to be.