Taste and smell that fluctuate, working fine one day and fading the next, usually point to an ongoing process in your nose or nervous system rather than permanent damage. In fact, that fluctuation is often a good sign: it suggests the sensory cells responsible for detecting odors are still functional, even if something is periodically blocking or disrupting them. The most common culprits are nasal inflammation from allergies or sinus problems, recovery from a viral infection, and environmental exposures, though neurological conditions can play a role too.
Nasal Inflammation and Sinus Disease
The single most common reason smell and taste come and go is inflammation inside your nose and sinuses. Allergic rhinitis causes smell problems in roughly 21 to 23 percent of people who have it, and taste disorders in about 31 percent. When your nasal lining swells from allergens like pollen, dust mites, or pet dander, it doesn’t just block airflow to the smell receptors high in your nose. The inflammation itself damages the tissue those receptors sit in. Research shows that the olfactory impairment in persistent allergic rhinitis is driven more by this inflammatory damage than by simple nasal congestion.
This explains why the fluctuation tracks your allergy exposure. On a low-pollen day or after taking an antihistamine, your sense of smell rebounds. During a flare, it fades again. The pattern creates a continuum: mild seasonal allergies might cause occasional dips, while chronic sinusitis or nasal polyps can produce more dramatic swings between near-normal smell and barely detecting anything at all.
Chronic rhinosinusitis with nasal polyps is a more advanced version of the same process. Polyps are soft, noncancerous growths that form from prolonged inflammation and can physically obstruct airflow. As polyps swell and shrink in response to inflammation, infections, or steroid treatment, your smell ability shifts accordingly. Clinicians actually consider a history of fluctuating smell sensitivity to be an encouraging sign in these patients, because it indicates the underlying sensory tissue is still working and may respond well to treatment.
Recovery After a Viral Infection
If your smell and taste started fluctuating after a cold, flu, or COVID-19 infection, the explanation lies in how your olfactory neurons heal. Unlike most nerve cells in the body, the smell receptors in your nose can regenerate. But that regeneration process is imperfect, and it takes time, typically 45 to 60 days after the initial infection for the new neurons to grow back.
During this recovery window, you may notice your smell cutting in and out or, more disturbingly, familiar things smelling wrong. A cup of coffee might smell like garbage, or cooking onions might trigger a burning chemical odor. This distortion, called parosmia, happens because the regenerating nerve fibers don’t always reconnect to the correct targets in your brain. Think of it like re-wiring a switchboard in the dark: some connections land in the right place, others don’t, and the result is a scrambled signal your brain interprets as a foul or unfamiliar smell.
There’s also a simpler mechanical explanation. When only some of your receptor types have regenerated, you’re only picking up certain components of a complex odor while missing others. Most smells are made up of dozens of chemical compounds. If you can only detect the pungent, low-threshold molecules without the balancing pleasant ones, the overall perception shifts dramatically. This incomplete detection model explains why parosmia triggers tend to be consistent across patients: foods like coffee, chocolate, meat, and garlic all contain volatile compounds that are detectable at extremely low concentrations, so they’re the first things your partially recovered nose picks up, but without the full picture.
About 5 to 10 percent of people with COVID-related smell loss don’t fully recover. For the rest, the fluctuation is a phase. It can last weeks to months, but the general trajectory is toward improvement as more neurons regenerate correctly.
Environmental Chemical Exposure
If you work around strong chemicals or have recently moved into a newly renovated space, your fluctuating smell may be a form of sensory desensitization. Controlled studies have shown that as little as two weeks of daily exposure to a volatile chemical in a home environment can significantly reduce your ability to detect that chemical, and irritants in general. The process happens at the receptor level in your nose: the cells essentially dial down their sensitivity to protect themselves from constant stimulation.
The good news is that this type of smell loss is reversible. In one study tracking participants for a full year after exposure ended, sensitivity returned to baseline levels for the majority of subjects. If you notice your smell is worse during the workweek and better on vacations or weekends away from a particular environment, chemical desensitization is worth considering.
Migraines and Neurological Causes
Migraines can temporarily alter your sense of smell in ways that mimic other conditions. Some migraine sufferers experience phantom smells, most commonly cigarette smoke or burning, as part of their aura phase. These olfactory hallucinations typically appear 30 minutes or so before the headache, though in some cases they persist for days afterward. The mechanism is the same wave of altered brain activity (cortical spreading depression) that causes visual aura symptoms like flashing lights or blind spots, just affecting the brain’s smell-processing areas instead.
If your smell changes reliably coincide with headaches, light sensitivity, or visual disturbances, migraines are a likely explanation. The fluctuation in this case isn’t about your nose at all. It’s about temporary disruptions in how your brain processes sensory input.
More rarely, progressive or unexplained smell loss can be an early marker of neurodegenerative conditions like Parkinson’s or Alzheimer’s disease, or can result from tumors pressing on the olfactory pathways. This is more concerning when the loss is gradual and worsening over time rather than truly coming and going, and when it’s accompanied by other neurological symptoms like tremors, memory changes, or balance problems.
Why Taste Follows Smell
Most people who report losing their taste are actually experiencing smell loss. True taste, the ability to detect sweet, sour, salty, and bitter on your tongue, relies on a completely separate set of nerves and is rarely affected by the conditions above. But what we experience as “flavor” is overwhelmingly driven by smell. When odor molecules from food can’t reach the receptors in your upper nose (either because of swelling or because those receptors are damaged), food tastes flat and one-dimensional even though your tongue is working perfectly fine.
This is easy to test at home: if you can still tell the difference between sugar water and salt water, your taste is intact. What you’re missing is the smell component that makes an orange taste different from a grapefruit, or makes chicken taste different from pork.
Olfactory Training for Recovery
One of the most evidence-backed strategies for speeding recovery is olfactory training, essentially a structured smell workout. The standard protocol involves sniffing four essential oils (rose, eucalyptus, clove, and lemon) for about 15 seconds each, twice a day, with a brief pause between each scent. Some protocols expand this to eight scents, adding options like mint, vanilla, and cedarwood.
In a multicenter clinical trial of post-COVID patients, 81.3 percent reported subjective improvement after just four weeks of training. Objective smell test scores also improved significantly across groups. Interestingly, patients who had fluctuating smell at the start of the study tended to score better on formal smell tests than those with stable loss, reinforcing the idea that fluctuation signals a system that’s actively trying to recover.
The training works by encouraging the regenerating neurons to form correct connections, similar to physical therapy after an injury. Consistency matters more than intensity. Twice a day, every day, for at least a month is the minimum commitment, and many clinicians recommend continuing for three to six months.
How Doctors Evaluate Fluctuating Smell
If your symptoms persist or worsen, a clinical evaluation typically starts with a detailed history of when the changes began, what makes them better or worse, and whether you’ve had any recent infections. A nasal endoscopy, where a thin camera is guided into your nasal passages, lets the doctor look for polyps, swelling, or structural issues that might be blocking airflow to the smell receptors.
Formal smell testing uses standardized kits that measure three distinct abilities: your threshold (the faintest concentration you can detect), your discrimination (whether you can tell two similar smells apart), and your identification (whether you can name what you’re smelling). Taste is screened separately using sprays of sweet, sour, salty, and bitter solutions on the tongue. Together, these tests help distinguish whether the problem is in your nose, your nerves, or your brain, and whether the fluctuation pattern suggests a condition likely to improve on its own or one that needs targeted treatment.