A sense of smell that comes and goes is surprisingly common, affecting roughly one in five adults to some degree. The fluctuation usually points to one of a handful of causes: nasal inflammation that periodically blocks airflow, nerve damage that’s slowly repairing itself, or an underlying condition that waxes and wanes. The good news is that most causes are treatable or resolve on their own, and the on-and-off pattern often means the system is still functional enough to recover.
How Your Nose Actually Detects Smell
To understand why smell flickers in and out, it helps to know how it works. Air carrying odor molecules enters your nose and travels up to a small patch of tissue called the olfactory cleft, tucked high in the nasal cavity. Specialized nerve cells there detect the molecules and send signals directly to the brain. Two things need to happen for this to work: air has to physically reach that patch, and the nerve cells have to be healthy enough to process the signal. When either step is disrupted, even partially or temporarily, your sense of smell drops out.
Sinus Congestion and Nasal Polyps
The most common reason smell comes and goes is simple: something is blocking airflow to the olfactory cleft, and that blockage shifts throughout the day. Allergies, sinus infections, and colds all cause swelling inside the nose that can narrow the passage to those smell receptors. When the swelling goes down (after a hot shower, a change in position, or when medication kicks in), smell returns. When it flares again, smell fades.
Nasal polyps are a particularly common culprit for the on-and-off pattern. These soft, noncancerous growths develop inside the nasal passages and sinuses, and they interfere with smell in two ways. First, they physically block air from reaching the olfactory cleft, acting like a valve that shifts with head position or swelling levels. Second, the chronic inflammation surrounding the polyps can damage the smell-detecting nerve tissue itself. This is why polyp-related smell loss can feel unpredictable: some days the airflow is better, some days the inflammation is calmer, and your ability to smell shifts accordingly.
Recovery After a Viral Infection
If your fluctuating smell started after a cold, flu, or COVID-19 infection, you’re likely experiencing the nerve repair process in real time. Viruses can damage or destroy the specialized nerve cells responsible for detecting odors. Unlike most nerve cells in the body, olfactory neurons can regenerate, but the process is slow and uneven.
New smell receptors typically take around 45 to 60 days to regrow after viral damage. During that window and beyond, your sense of smell may return in patches. You might pick up certain scents one day and lose them the next, or detect only parts of a complex smell. This happens because the regenerating nerve fibers don’t always reconnect to the correct targets in the brain. Think of it like a phone system being rewired: some lines work, some are crossed, and the result is inconsistent service.
This incomplete rewiring also explains why some people experience parosmia, where familiar smells become distorted or unpleasant, during recovery. Research suggests this occurs because only certain types of odor receptors have regrown, particularly those tuned to detect highly volatile compounds at low concentrations. Without the full set of receptors working, your brain gets a lopsided version of the smell, and usually an unpleasant one. As more receptors come back online, these distortions typically fade. About 5% to 10% of people with COVID-related smell loss don’t fully recover, but the majority do improve over months.
Aging and Gradual Decline
If you’re over 60, age-related changes may explain the inconsistency. The number of working olfactory nerve cells declines naturally over time, and the remaining cells become less efficient. This doesn’t always show up as a steady fade. Instead, you might notice your sense of smell is stronger on some days than others, or that you can detect strong odors but miss subtle ones. About 13% to 18% of the general population has reduced smell (hyposmia), and the rate climbs significantly with age. Many people don’t even realize it: when researchers use standardized scratch-and-sniff tests, nearly 29% of people show measurable smell loss, compared to only about 10% who report noticing it themselves.
Medications and Chemical Exposures
Certain medications can dull your sense of smell as a side effect, and if you take them inconsistently or change doses, that could explain the fluctuation. Common antibiotics and antihistamines are among the known offenders. Ironically, the antihistamines many people take for allergies (which also cause smell loss) can themselves contribute to the problem. Prolonged exposure to chemicals like insecticides, solvents, or industrial fumes can also damage olfactory tissue, sometimes in ways that heal partially and then flare up again with re-exposure.
If you suspect a medication is involved, check whether your smell changes align with when you take it. A pattern there is worth bringing up with your doctor.
Hormonal and Neurological Causes
Hormonal shifts can temporarily alter smell sensitivity. Some women notice their sense of smell fluctuates with their menstrual cycle, during pregnancy, or around menopause. These changes are usually mild and resolve when hormone levels stabilize.
Less commonly, neurological conditions play a role. Migraines can cause temporary smell distortions or phantom smells (detecting an odor that isn’t there) as part of the aura phase, though this is rare. More seriously, a declining sense of smell can be an early sign of Parkinson’s disease or Alzheimer’s disease, sometimes appearing years before other symptoms. A smell that comes and goes isn’t a hallmark of these conditions on its own, but if the overall trend is downward and you’re noticing other changes in memory or movement, it’s worth investigating.
Olfactory Training to Speed Recovery
If your smell loss is related to viral damage or is otherwise slowly improving, olfactory training is the most evidence-backed way to help it along. The protocol is straightforward: smell four distinct scents (rose, eucalyptus, lemon, and clove) twice a day, spending about 15 seconds on each one with a 10-second rest between them. While you smell each one, actively try to recall what it used to smell like. This mental effort appears to help the regenerating nerve cells find their correct connections.
After three months, switch to a new set of scents (menthol, thyme, tangerine, and jasmine) and continue the same routine. After another three months, switch again (green tea, bergamot, rosemary, and gardenia). The whole process takes about nine months. It requires patience, but studies consistently show it improves outcomes compared to doing nothing.
When Inflammation Is the Problem
For smell loss driven by nasal inflammation, whether from polyps, chronic sinusitis, or allergies, reducing the swelling is the primary approach. Nasal corticosteroid sprays are the usual first step. These work locally with minimal absorption into the body (less than 1% enters the bloodstream), making them safe for extended use. In one study of patients with prolonged smell loss, anosmia rates dropped by about 23% with nasal steroid treatment compared to placebo.
Oral corticosteroids tend to produce stronger results, particularly for stubborn cases, but come with more side effects and are typically used in short courses. For polyp-related smell loss that doesn’t respond to medication, surgical removal of the polyps can restore airflow to the olfactory cleft, though polyps sometimes recur. Newer biologic medications that target the specific inflammatory pathways behind polyp growth have shown promising results for both polyp reduction and smell recovery.
What the Pattern Tells You
Pay attention to when your smell disappears and when it returns. If it tracks with allergy seasons, congestion, or specific environments, the cause is likely inflammatory or mechanical. If it started after an illness and has been gradually improving with occasional setbacks, you’re probably in the nerve regeneration phase. If it seems random and you also experience headaches, the neurological connection is worth exploring.
The intermittent nature of your smell loss is actually a useful signal. Complete, permanent loss suggests more serious damage, while a sense of smell that keeps coming back, even inconsistently, means the underlying system is still working. That’s the foundation recovery builds on.