Changes in taste and smell usually stem from the same source: your sense of smell is doing far more work than you realize. What most people experience as “taste” is actually flavor, and roughly 80% of flavor perception comes from smell rather than your taste buds. When odor molecules travel from the back of your throat up into your nasal cavity while you eat, your brain processes that information alongside taste signals. So when your smell is even slightly reduced, food tastes bland, metallic, or just wrong.
The most common reasons for disrupted taste and smell are viral infections, medications, nutritional deficiencies, nasal congestion, and aging. Less commonly, the change signals something neurological worth investigating. About 3% of Americans have lost their sense of smell entirely or nearly so, and 1 in 20 reports persistently distorted taste.
Viral Infections Are the Leading Cause
A cold, flu, or sinus infection can knock out your sense of smell temporarily by inflaming the nasal lining. Swollen tissue physically blocks odor molecules from reaching the smell receptors high inside your nose. Once the congestion clears, smell typically returns within days.
COVID-19 works differently. The virus directly infects the support cells that surround and nourish your smell-sensing neurons, disrupting the signaling pathway even without significant nasal congestion. This is why many people with COVID lost their sense of smell without ever feeling stuffed up. Other respiratory viruses like rhinovirus and parainfluenza can occasionally damage smell this way too, but it happens far less frequently than with COVID.
The good news is that most post-viral smell loss resolves on its own. For COVID specifically, most people notice substantial improvement within two weeks. About 74% report recovered smell after 30 days, and roughly 96% recover by six months. Recovery can continue for at least two years after infection. However, an estimated 5% develop persistent dysfunction, experiencing lasting reduction or distortion in how things smell and taste.
Medications That Alter Taste
Medications are actually the single most common cause of taste disorders overall, responsible for about 22% of cases. The effect cuts across nearly every drug category, but three groups cause the most problems: cancer treatments, antibiotics and antifungals, and drugs that act on the nervous system (including some antidepressants and anti-seizure medications). Blood pressure medications that work by blocking a specific enzyme involved in fluid regulation are another well-known culprit, often producing a persistent metallic taste.
If your taste or smell shifted around the time you started a new medication, that connection is worth exploring with whoever prescribed it. Drug-induced taste changes are often reversible once the medication is stopped or swapped, though some take weeks to fully resolve.
Zinc Deficiency and Taste Bud Health
Zinc plays a direct role in how your taste buds grow and function. Your saliva contains a zinc-dependent protein that supports taste bud development. When zinc levels drop, this protein decreases too, and the taste buds themselves can physically change shape and stop working properly. Zinc deficiency accounts for roughly 15% of taste disorder cases.
The resulting symptoms vary. Some people experience a general dulling of all five taste qualities (sweet, sour, bitter, salty, and savory). Others develop dysgeusia, a persistent foul, metallic, or rancid taste that lingers regardless of what they eat. People at higher risk for zinc deficiency include older adults, vegetarians, people with digestive conditions that impair absorption, and heavy alcohol users.
Other nutritional gaps, particularly in B vitamins, can contribute as well, though zinc is the most thoroughly documented.
Nasal and Sinus Problems
Chronic sinusitis, nasal polyps, and severe allergies all reduce smell by physically obstructing airflow to the olfactory region. Unlike viral damage, this type of smell loss tends to fluctuate. You might notice it worsens during allergy season or when a sinus flare-up hits, then partially improves. If your smell loss tracks with congestion, stuffiness, or facial pressure, the underlying nasal condition is the likely driver.
Age-Related Decline
Smell function peaks in your 30s and 40s, then gradually declines. By age 60, the decrease becomes more noticeable, and by 80, a significant percentage of people have measurable smell loss. Taste buds also regenerate more slowly with age, though pure taste loss (without smell involvement) is less dramatic than most people assume. The combination of slower taste bud turnover and reduced smell sensitivity is why food often seems less flavorful to older adults.
Smell Loss as a Neurological Signal
A declining sense of smell can sometimes be an early marker of neurodegenerative conditions, appearing years before other symptoms. In Parkinson’s disease, smell loss is one of the earliest detectable changes. One study followed 44 Parkinson’s patients over three years and found that every single patient who went on to develop dementia had severe smell dysfunction at the start of the study. Patients with the worst smell scores had an 18-fold increased risk of developing dementia for each standard deviation their scores dropped.
Alzheimer’s disease also involves early olfactory decline, as the brain regions processing smell overlap with those affected early in the disease. Multiple sclerosis can cause episodes of smell disturbance alongside other neurological symptoms that come and go.
This does not mean that a stuffy nose or post-cold smell loss points to neurological disease. The red flags that warrant prompt evaluation are: smell loss that came on suddenly without any infection, smell loss accompanied by confusion or memory changes, other neurological symptoms like weakness, numbness, difficulty speaking or swallowing, or a history of head injury.
How Smell Training Works
If your smell hasn’t bounced back after a viral infection, smell training is the most evidence-backed rehabilitation technique. The protocol is simple: twice a day, you spend about 20 seconds sniffing each of four distinct scents, typically rose, eucalyptus, lemon, and clove. These four were chosen because they each activate a different type of smell receptor.
The results are meaningful. In a study of over 100 patients with post-infectious smell loss, 71% improved with smell training over one year, compared to only 37% who recovered spontaneously without training. For smell loss caused by head trauma, the numbers are lower but still significant: 23% improved with training versus 5% without it. Patients with Parkinson’s-related smell loss see the smallest benefit, with about 20% improving through training compared to 10% recovering on their own.
Consistency matters more than intensity. Most protocols recommend continuing for at least 12 weeks before judging whether it’s working, and many people continue for several months.
Getting Your Smell Tested
If you’re unsure how much smell function you’ve actually lost, standardized scratch-and-sniff tests can quantify it. The most widely used version in the U.S. presents 40 odors to identify, with scores adjusted for gender and age. A shorter 12-item version is commonly used in clinical settings, where a score of 8 or below (out of 12) flags abnormal function. These tests help distinguish between partial loss, complete loss, and distorted smell, which guides what type of treatment or training is most appropriate.