Brief overview
- What is anosmia? Loss of the ability to smell. Like partial loss of the sense of smell (hyposmia), anosmia is one of the olfactory disorders (dysosmia).
- Frequency: Anosmia affects an estimated five percent of people in Germany. The frequency of this olfactory disorder increases with age.
- Causes: e.g. viral respiratory infections such as colds with rhinitis, sinusitis or COVID-19, allergic rhinitis, atrophic rhinitis (a form of chronic rhinitis), nasal polyps, deviated nasal septum, medication, pollutants and toxins, Parkinson’s disease, Alzheimer’s disease, multiple sclerosis, head trauma, brain tumor, etc.
- Diagnosis: doctor-patient consultation, ENT examination, olfactory tests, further examinations if necessary
- Treatment: depending on the cause, e.g. with medication (such as cortisone), surgery (e.g. for nasal polyps), olfactory training; treatment of underlying diseases
Depending on where the cause of the impaired olfactory perception is to be found, doctors divide olfactory disorders such as anosmia into sinunasal and non-sinunasal:
Sinunasal olfactory disorder
Anosmia or other olfactory disorders are described as sinunasal if the cause is a disease or change in the nose and/or paranasal sinuses. The function of the olfactory mucosa in the upper nasal passage is impaired due to inflammation and/or the path of the inhaled air to the olfactory mucosa is more or less blocked.
A loss of smell is also typical for the coronavirus infection Covid-19, where anosmia often occurs as an early symptom. Exactly how it occurs is not yet fully understood. However, several factors are probably involved, such as swelling of the nasal mucosa (sinunasal cause), damage to the olfactory mucosa and disruption of the olfactory signaling pathway in the brain (non-sinunasal causes, see below).
Another possible cause of a sinunasal-related olfactory disorder is allergic rhinitis: if the nasal mucosa becomes inflamed and swollen as a result of hay fever or a house dust allergy, for example, those affected can only smell to a limited extent or not at all.
In other cases, anosmia occurs in connection with so-called atrophic rhinitis. In this form of chronic rhinitis, the mucous membrane becomes thinner and hardens. This often occurs in older people and those who suffer from granulomatosis with polyangiitis (Wegener’s disease). Atrophic rhinitis with subsequent anosmia can also develop after sinus surgery and with prolonged bacterial infections of the nasal mucosa.
Tumors in the nose or paranasal sinuses can also block the path of the air we breathe to the olfactory epithelium.
Non-sinunasal olfactory disorder
Non-sinunasal olfactory disorders are those caused by damage to the olfactory apparatus itself (olfactory mucosa, olfactory tract).
Very often this is a post-infectious olfactory disorder. This is a persistent disorder of the sense of smell following a temporary infection of the (upper) respiratory tract, with no symptom-free interval between the end of the infection and the onset of the olfactory disorder. In addition, up to 25 percent of those affected perceive odors differently (parosmia) or report odor hallucinations (phantosmia). Post-infectious olfactory disorders are probably mainly caused by direct damage to the olfactory mucosa (olfactory epithelium).
Other possible causes of a non-sinunasal olfactory disorder are
- Craniocerebral trauma: In the event of a fall or blow to the head, olfactory nerves can be completely or partially severed. Or bruising or bleeding can occur in areas of the brain that are responsible for perceiving and processing olfactory stimuli. The partial or complete loss of the sense of smell (hyposmia or anosmia) occurs quite suddenly in such traumatic brain injuries.
- Toxic and harmful substances: They can cause acute and chronic damage to the olfactory mucosa and thus cause a non-sinus olfactory disorder (e.g. in the form of anosmia). Possible triggers are formaldehyde, tobacco smoke, pesticides, carbon monoxide and cocaine. In the same way, radiotherapy can trigger a loss of smell (anosmia) or partial loss of smell (hyposmia) in cancer patients.
- Medication: Some medicines can cause a non-sinunasal olfactory disorder as a side effect. These include antibiotics (e.g. amicacin), methotrexate (used in higher doses as a cancer drug), antihypertensive drugs (e.g. nifedipine) and painkillers (e.g. morphine).
- Operations, infections and tumors inside the skull: Surgery and tumors inside the skull as well as central nervous system infections can disrupt the olfactory signaling pathway, causing non-sinunasal olfactory dysfunction.
- Age: The ability to smell naturally declines with increasing age. However, Parkinson’s or Alzheimer’s disease should always be considered as a possible cause in older people with loss of smell.
If no cause for an olfactory disorder can be found, doctors diagnose an “idiopathic olfactory disorder”. This is therefore a diagnosis of exclusion.
Anosmia: symptoms
Loss of smell is the central characteristic of anosmia. Strictly speaking, however, doctors differentiate between functional and complete anosmia:
- Functional anosmia: The sense of smell is so severely impaired that it can no longer be used sensibly in everyday life – even if a few odors can still be perceived occasionally, weakly or briefly. However, this residual sense of smell is insignificant.
Whether functional or complete anosmia – the everyday experience of those affected is simple: “I can no longer smell”, i.e. I can no longer ask my own nose whether the milk is sour, the T-shirt from the previous day smells of sweat or the perfume gift from my partner is a hit or a miss.
In addition, many people with anosmia have problems with their sense of taste: most of them can taste salty, sour, sweet and bitter things normally, but cannot distinguish between certain flavors. This is because not only the taste receptors but also the olfactory receptors on the tongue are needed for this – only in combination can a flavor fully unfold.
Anosmia: Consequences
With the loss of smell, however, not only the enriching function of smell is lost, but also its warning function: people with anosmia cannot smell, for example, when food is burning on the hob, food has spoiled or the gas heating has sprung a leak.
Similarly, people with anosmia cannot detect the smell of sweat or a bad smell in the bathroom or kitchen. The knowledge that, unlike themselves, other people can notice this very well can put a great deal of psychological strain on anosmia sufferers.
Anosmia: therapy
Whether and how a disturbed sense of smell can be restored depends on its cause.
Chronic rhinosinusitis without nasal polyps is treated in adults with local cortisone preparations (spray) and saltwater nasal rinses. The cortisone has an anti-inflammatory effect; the nasal rinsing helps to loosen stuck mucus. If bacteria are involved, the doctor sometimes also prescribes antibiotics.
It is best to apply the cortisone spray “upside down”. If you inject the spray into both nostrils in an upright position, only a small amount of the active ingredient will reach its destination. If you use the spray upside down, on the other hand, more cortisone reaches the olfactory mucosa in the nasal cavity.
Nasal polyps themselves are very often surgically removed. This improves nasal breathing and – if the polyps have blocked the entrance to the sinuses – reduces the risk of recurrent sinusitis. Both can improve an impaired sense of smell. If you have a tumor in your nose or sinuses blocking the path of inhaled air to the olfactory epithelium, surgery is also usually performed. The same applies if a curved nasal septum causes hyposmia or anosmia as an obstacle in the airflow.
If an olfactory disorder is due to allergic rhinitis, local cortisone preparations are the most promising treatment option. Regardless of whether and to what extent the affected person’s sense of smell is impaired, the allergy itself can be treated as required (e.g. avoid allergens as far as possible, possibly hyposensitization).
There are no general treatment guidelines for anosmia or other olfactory disorders caused by other forms of rhinitis (such as rhinitis of unknown cause = idiopathic rhinitis). Instead, individual treatment attempts are recommended in such cases.
If medication triggers the loss of smell, the treating doctor can check whether the preparation can be discontinued. The olfactory disorder will then usually disappear. If discontinuation is not possible, the dosage can sometimes be reduced. This can at least improve the ability to smell.
Under no circumstances should you discontinue prescribed medication on your own initiative or reduce the dosage! Always discuss this with your doctor first.
Structured olfactory training is also recommended for patients with post-infectious olfactory disorders. If possible, training should be started within the first year after the onset of the olfactory disorder. If necessary, drug treatment can also be tried (in addition), for example with cortisone.
If underlying diseases such as Alzheimer’s, multiple sclerosis or brain tumors are behind the (partial) loss of the sense of smell, their specialist treatment is paramount.
No treatment is possible for congenital and age-related anosmia.
Olfactory training
As mentioned, experts recommend structured olfactory training, especially for post-infectious olfactory disorders. This can also be useful for olfactory disorders following a traumatic brain injury.
Olfactory training pens are also used in a similar way for the diagnosis of olfactory disorders (see below). As an alternative to such pens, some people use vials of pure essential oils for olfactory training.
You can also use your memory to help you train your sense of smell. For example, try to remember the exact smell of freshly baked cinnamon stars or freshly ground coffee. Or think about what the air smells like when a heavy downpour breaks out on a hot summer’s day.
Tips for everyday life
- Smoke alarms in your own four walls are always important – but especially if you suffer from anosmia and are therefore unable to detect the smell of burning at an early stage.
- Do you still have at least some of your sense of smell? Then adding concentrated aromas to your food can make it more tasty and enjoyable.
- Store your food properly. If necessary, make a note of the date of purchase and the opening date (e.g. for cans or milk cartons). Use the food within the recommended period. Also remember: In addition to smell and taste, the consistency and color of some foods can also indicate spoilage.
- Some people with anosmia stick to fixed schedules for personal hygiene, changing clothes and cleaning the bathroom and kitchen. After all, their own nose cannot signal when it is time for such activities. The fixed schedules give those affected a sense of security when it comes to their own cleanliness and that of their home – often a great psychological relief.
Medical history
In order to clarify an olfactory disorder, the doctor will first take your medical history (anamnesis). To do this, he will ask you about your symptoms and possible causes of an olfactory disorder. Possible questions include, for example
- How long have you been unable to smell anything?
- Have you suddenly lost your sense of smell or has the olfactory disorder developed slowly?
- Is the loss of smell complete or can you still perceive individual, faint odors?
- Do you have any other symptoms, such as problems with tasting?
- Do you have/have you had an upper respiratory tract infection that could be related to the olfactory disorder?
- Did you have a head injury or an operation before you lost your sense of smell?
- Do you have any pre-existing medical conditions, such as chronic sinusitis or allergies?
- Are you taking any medication and if so, what is it?
Physical examination
The medical history interview is followed by an ENT examination including a nasal endoscopy (rhinoscopy). During the detailed examination of the nose, nasopharynx, paranasal sinuses and olfactory cleft (the region in the upper nasal passage where the olfactory mucosa is located), the doctor will look for signs of swelling, inflammation, nasal polyps and discharge.
They may also ask you to breathe through each nostril in turn while holding the other one closed with your hand. This will reveal whether the airflow on one side may be obstructed.
Smell test
Here are some test procedures in detail:
Sniffin’ sticks
“Sniffin’ sticks” (olfactory sticks) are felt-tip pens filled with an odorant. They are the preferred test method for clarifying olfactory disorders because they are easy to carry out and different test variants are possible.
For example, the olfactory pens can be used to carry out an identification test. This tests the patient’s ability to recognize and distinguish between different scents. To do this, the doctor holds 12 or 16 different “sniffin’ sticks” under both nostrils of the patient one after the other. The patient should try to identify the respective scent with the aid of a selection card on which all the scents are indicated.
UPSIT
The abbreviation UPSIT stands for University of Pennsylvania Smell Identification Test. In this process, 40 different fragrances packaged in microcapsules are applied to paper. As soon as a capsule is rubbed with a pen, the respective scent is released. The patient is asked to try to identify it from a list of four words.
CCCRC
The Conneticut Chemosensory Clinical Research Center (CCCRC) test combines an identification test and a threshold test: In the identification test, the patient has to recognize and name ten different scents presented to them in glass or plastic vials. In addition, the olfactory threshold is tested with butanol solutions of different concentrations.
Measurement of olfactory potentials
As test substances, the doctor holds various pure fragrances in front of the patient’s nose one after the other, for example rose fragrance (chemical: phenylethyl alcohol). It normally triggers only a weak excitation of the olfactory nerves. This is in contrast to hydrogen sulphide, for example, with its intense smell of rotten eggs.
The measurement of olfactory potentials is very complex. It is therefore only carried out in specialized clinics and medical practices.
Other tests
Anosmia: progression & prognosis
Basically, olfactory disorders such as anosmia are not easy to treat and the ability to smell cannot always be normalized again. The chances of success are generally better for younger patients and non-smokers than for older people and smokers. However, precise prognoses are not possible, only general indications:
Anosmia or hyposmia in the context of an acute viral infection of the (upper) respiratory tract such as nasal mucosal inflammation (rhinitis) or sinusitis is not usually a cause for concern. The olfactory disturbance is usually temporary and improves again once the infection has healed. In the case of long-term inflammation, however, the sense of smell can be permanently impaired or completely lost because the olfactory epithelium is progressively destroyed or remodeled.
If drugs, toxins or pollutants are the cause of an olfactory disorder, the ability to smell may improve again once these substances have been discontinued (e.g. after chemotherapy). However, irreversible damage with a permanent olfactory disorder is also possible, for example if acids have destroyed the basal layer of the olfactory epithelium.
In around two thirds of all patients with post-infectious olfactory disorders, the sense of smell improves spontaneously within one to two years. In the remainder, the impaired sense of smell or loss of smell remains permanent. In general, the younger a patient is and the shorter the duration of the disorder, the higher the chances of improvement.
- high residual creep
- female gender
- young age
- non-smoker
- no side differences in olfactory function
- Smell disorder has not existed for so long
In the case of olfactory disorders associated with underlying diseases such as Parkinson’s, Alzheimer’s or diabetes, it is not possible to predict whether and to what extent the ability to smell will improve again as a result of treatment of the underlying disease.
The natural age-related decline in the sense of smell cannot be stopped or remedied. There is also nothing that can be done about congenital anosmia.
