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Suddenly can't smell anything? Causes from post-COVID and polyps to Parkinson's, olfactory training, tests, and when medical evaluation is needed.
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When to see a doctor: smell disorder lasting more than 4 weeks, one-sided, with neurological symptoms, accompanying symptoms, or a significant loss of quality of life
A smell disorder — summarized medically as dysosmia — refers to any change in normal smell perception. This ranges from mild reduction to a distorted perception of individual scents and all the way to a complete loss of the sense of smell (anosmia). In Germany, about 5 percent of the population are affected by a relevant smell disorder, and as many as 25 percent from age 65 — many of them without ever being evaluated by a doctor.
Smell disorders are often underestimated — by those affected and by their care providers alike. Yet they affect quality of life about as much as hearing or vision loss: food loses its appeal, safety risks increase (burnt food, gas, and smoke go unnoticed), emotional experience changes (scents are closely tied to memories), and social situations such as cooking or wine and cheese tasting lose their depth. Studies show higher rates of depression and reduced life satisfaction in people with anosmia.
With the COVID-19 pandemic, smell disorders suddenly entered public awareness — it was one of the most characteristic symptoms of the illness and still affects millions of people worldwide in the post-COVID phase. At the same time, a smell disorder can be the early sign of serious neurological diseases — Parkinson's disease and Alzheimer's dementia often begin with a gradual reduction in smell that goes unrecognized for years.
The sense of smell is neuroanatomically fascinating: in the upper part of the nasal cavity, at the so-called olfactory epithelium, there are about 350 different smell receptors — a far greater variety than the sense of taste with its mere 5 basic qualities. These receptors recognize different odor molecules and send the information via the olfactory nerve (cranial nerve I) directly to the brain — without the "detour" through other brain structures that most other senses take.
This direct connection to the limbic system explains why smells are so strongly tied to emotions and memories — the scent of a perfume or an old chalkboard can call up entire worlds of experience. At the same time, the anatomy makes the sense of smell vulnerable: the thin olfactory epithelium is in direct contact with the outside world and is exposed, unprotected, to pollutants, viruses, bacteria, and injury.
Important to understand: we smell via two routes — orthonasally when actively breathing in through the nose, and retronasally when eating, as odor compounds rise from the mouth and throat. The latter accounts for about 80 percent of what we perceive as "taste" — hence the close link to taste disorders. Anyone who can no longer smell properly automatically tastes less.
ENT medicine distinguishes clearly defined forms that are relevant for diagnosis and treatment:
Clinically, parosmia and phantosmia are particularly distressing — and have become much more common because of SARS-CoV-2. Some patients report unbearable smell distortions for years that can turn every meal into an ordeal. These forms are often harder to treat than simple anosmia.
SARS-CoV-2 infects the supporting cells of the olfactory mucosa and causes acute loss of smell in a large proportion of those who fall ill. Depending on the virus variant, this affects 30 to 80 percent of all COVID-19 patients — and thus millions of people worldwide.
Acute course: the loss of smell typically appears in the first few days after symptom onset, often as an isolated early symptom with no other complaints. Most of those affected recover fully within 1 to 4 weeks. In a relevant share, however — around 5 to 10 percent — the complaints persist for more than 6 months.
Post-COVID phase: characteristic here are parosmias and phantosmias, which are not rare — coffee suddenly smells of gasoline, meat of decay, onions of chemicals. These distortions can be tormenting and can ruin meals. They are a sign that the smell neurons are regenerating — but are still "wired up" incorrectly at first. Patience is crucial here: studies show that marked improvements are still possible even after 1 to 2 years.
Treatment of post-COVID anosmia: the most clearly proven option is olfactory training (see the dedicated section further below). If a zinc deficiency is documented, supplementation can be useful. Steroids (oral or as a nasal spray) have shown a limited effect in studies — recommended only when there is a clear sinusitis component. A specialized smell clinic can offer individual treatment options, for example plasma injections or topical pentoxifylline applications — both off-label.
The second most common cause after postviral smell disorders — especially chronic rhinosinusitis with nasal polyps (CRSwNP). Polyps are benign, grape-like growths of the mucosa in the nasal cavity that mechanically block odor compounds from reaching the olfactory epithelium. About 4 percent of the population are affected — men twice as often as women. Common associations: bronchial asthma, aspirin intolerance (Samter's triad), eosinophilic inflammation.
Symptoms: gradual or fluctuating loss of smell, obstructed nasal breathing, a feeling of pressure in the face, postnasal drip, a constant urge to clear the throat, frequent bouts of sinusitis. The diagnosis is made by ENT nasal endoscopy and a CT scan of the sinuses.
Treatment: highly effective corticosteroid sprays as first-line therapy, nasal rinses with isotonic or hypertonic saline, and, for pronounced polyps, surgical removal (FESS — functional endoscopic sinus surgery). For severe eosinophilic CRSwNP, biologics (dupilumab, mepolizumab, omalizumab) have been available for several years — they show a very good effect on the sense of smell and on polyp size.
Traffic accidents, falls, sports injuries — wherever a traumatic brain injury occurs, the fine smell fibers that run from the olfactory epithelium through the cribriform plate to the olfactory bulb can be torn. Even minor injuries with brief loss of consciousness can lead to anosmia — sometimes noticed immediately, sometimes only days or weeks later.
Prognosis: post-traumatic smell disorders recover more slowly than postviral ones — partial recovery is possible within 1 to 2 years, but about half of those affected retain a relevant residual anosmia. Olfactory training can be helpful here too.
Forensic significance: a trauma-related anosmia is a significant impairment for occupations that require a sense of smell (chefs, sommeliers, perfumers, firefighters, food chemists) and can be relevant in insurance terms. An objective smell test by an ENT doctor is important here.
About 90 percent of all people with Parkinson's disease have a relevant smell disorder — often years, sometimes decades, before the first motor symptoms (resting tremor, bradykinesia, rigidity). The smell disorder is among the earliest neuropathological changes — Lewy bodies, the protein deposits typical of Parkinson's disease, are already found in the olfactory bulb and in neighboring brain regions.
Clinical significance: isolated anosmia without sinusitis, without preceding trauma, and with no other explanation — especially in middle or older adulthood — should raise the suspicion of a prodromal Parkinson's disease. Other early signs include: REM sleep behavior disorder with strikingly active dreaming, constipation, mood swings and depression, mild cognitive changes, and increased sweating.
What to do: isolated anosmia alone does not justify a Parkinson's diagnosis — it is too nonspecific. Where prodromal signs cluster, a neurological assessment with targeted examination (a motor test and, if needed, a DAT-SPECT scan) can be useful. There is currently no established preventive treatment, but lifestyle factors (exercise, a healthy diet, social activity) are considered protective. More under tremor.
In Alzheimer's dementia, too, a smell disorder often precedes the clinical symptoms by years. The damage begins near the olfactory cortex, which is among the earliest brain regions to be affected. Studies show that pronounced anosmia markedly increases the risk of later dementia — though it is too nonspecific to serve as a screening tool on its own.
Other neurological causes: multiple sclerosis (in relapses), strokes in certain regions, brain tumors (especially meningiomas in the front of the skull), and epilepsy (in rare cases with an olfactory aura). An MRI scan is useful for an unclear one-sided smell disorder or one that is neurologically suspicious.
Medications and environmental toxins can impair the sense of smell too — usually reversibly after stopping the drug or the exposure:
Important: if a medication-related smell disorder is suspected, talk to a doctor before stopping the drug. With occupational exposure (painters, varnishers, chemical workers), make sure to use adequate respiratory protection. More: drug interactions.
About 1 in 10,000 people is born with a non-functioning sense of smell. Isolated congenital anosmia is usually genetic and affects the sense of smell with no other symptoms. A special form is Kallmann syndrome — a genetic condition in which the maturation of the pituitary gland, and thus puberty, is impaired at the same time (delayed or absent puberty, infertility, sometimes further anomalies).
Diagnosis: anosmia since birth (or as far back as childhood can be remembered), often with a small or absent olfactory bulb on MRI. In Kallmann syndrome, the sex hormones (LH, FSH, estradiol/testosterone) are typically low. Genetic counseling can be useful.
Treatment: there is no causal treatment for congenital anosmia. In Kallmann syndrome, hormone replacement is well established and enables normal pubertal development and, in many cases, fertility as well. The anosmia itself usually remains, but it can be compensated for well with adaptation and safety precautions.
In everyday life, people with anosmia are exposed to several serious dangers that are often overlooked — informing patients about them is part of the doctor's duty:
See an ENT doctor promptly if:
ENT smell diagnostics follow a structured approach:
More: preparing for a doctor's appointment, understanding blood test results.
Olfactory training is the most clearly evidence-based and, at the same time, side-effect-free treatment for postviral smell disorders, post-COVID anosmia, and also for traumatic or idiopathic forms. The principle: regular, targeted stimulation of the olfactory mucosa promotes the regeneration and re-wiring of the smell neurons.
First improvements are often only noticeable after 4 to 12 weeks — giving up early reduces the chances of success. In studies, about 30 to 60 percent of those who train benefit significantly, and some recover almost completely. Even when full recovery does not occur, the parosmias — and with them quality of life — often improve.
When an inflammatory component is documented (chronic sinusitis, nasal polyps), intranasal corticosteroid sprays (mometasone, fluticasone, beclomethasone) are very effective and safe for long-term use. During acute flare-ups, short-term systemic steroids (a prednisolone burst over 1–2 weeks) can be considered. For a purely postviral smell disorder without sinusitis, the effect is smaller.
For severe eosinophilic chronic rhinosinusitis with nasal polyps, dupilumab, mepolizumab, and omalizumab are very effective — they reduce polyp size and markedly improve the sense of smell. The indication is set in a specialized ENT clinic, often together with an assessment by an asthma specialist.
For polyps, pronounced septal deviation, or anatomical narrowing, functional endoscopic sinus surgery (FESS) is well established. It restores ventilation and drainage and can markedly improve the sense of smell. For purely postviral or traumatic anosmia, on the other hand, surgery brings no benefit.
When a zinc deficiency is documented, supplementation is useful. Vitamin A applied topically into the nose has shown signs of effectiveness in small studies — the evidence is still limited. Plasma injections (PRP) into the olfactory epithelium and topical pentoxifylline are being researched in specialized centers. Patients with treatment-resistant anosmia can turn to university smell clinics.
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