Loss of sense of smell or reduced sense of smell: causes

Anosmia is the name of a condition in which there is a complete loss of the sense of smell. You then completely lose your sense of smell. Anosmia can be congenital or acquired and different causes occur within both groups. Loss of smell can also occur partially. This is called ‘hyposmia’. There are several possible causes of loss of smell. The loss of smell can have a harmless cause, such as a cold or flu, but it can also be a symptom of a serious condition. Recovery from an olfactory disorder depends entirely on the cause. After a cold or flu, the sense of smell often recovers after a few days. Sometimes surgery is necessary, for example for nasal polyps. As of 2023, there is no effective treatment for olfactory disorders resulting from damage to the olfactory epithelium, nerve pathway or brain.

  • What is anosmia and what is hyposmia?
  • Types of olfactory disorders
  • The possible consequences of loss of smell
  • Causes partial or total loss of smell
  • No longer smelling anything due to a cold or flu
  • Permanent nasal congestion
  • Surgery, trauma, smoking and cocaine
  • Smell reduced by medicines
  • Systemic diseases
  • Anosmia as part of a syndrome
  • Vitamin or mineral deficiency
  • Age
  • No underlying cause
  • Loss of smell due to nasal spray
  • Course of hyposmia
  • Examination and diagnosis
  • Interview and physical examination
  • Follow-up research
  • Smell tests
  • Restoration of sense of smell and possible treatment
  • Treatment and spontaneous course
  • Conductive and sensorineural olfactory disorders
  • Acceptance and self-help groups
  • Complications of loss of sense of smell
  • Prognosis of loss of smell


What is anosmia and what is hyposmia?

Anosmia is the name of a condition in which there is a complete loss of the sense of smell. It is more common for a person to partially lose their sense of smell (hyposmia); a complete loss of the sense of smell is quite rare. Anosmia can be temporary or permanent depending on the cause. There are several possible causes of anosmia. Anosmia can have a harmless cause, but it can also be a symptom of a serious condition.

Types of olfactory disorders

An olfactory disorder or disorder in the sense of smell is also called ‘dysosmia’. Five types of olfactory disorders are distinguished:

  • Anosmia: the complete absence of the sense of smell.
  • Hyposmia: A partial loss of the sense of smell.
  • Parosmia: a distortion of the sense of smell.
  • Phantosmia: smelling something when there is nothing to smell.
  • Presbyosmia: A decrease in the sense of smell caused by old age.


The possible consequences of loss of smell

When someone can no longer smell, this can have major consequences, both practically and socially and interpersonally. Smell and taste are closely linked. You can taste certain substances better if you can also smell them and some substances you cannot taste with your tongue; you only ‘taste’ them when you smell them. If you put such a substance on your tongue while pinching your nose, you won’t taste anything.
Taste and smell
The taste buds of the tongue register taste and the sensory cells in your nose respond to different smells. Both sensations are transmitted to the brain, where the information is combined. This allows flavors to be recognized and assessed. The five main tastes (sour, salty, sweet, bitter and umami) can be recognized without the sense of smell, these are perceived by the taste buds on the tongue. But for more complex flavors (raspberries or cherries, for example), both taste and smell are necessary. The aroma of the food is perceived through your nose. People who suddenly experience anosmia can often only taste (very) little. They then taste only what the tongue can perceive: bitter, sweet, salty and sour. People with congenital anosmia have often developed some kind of taste.

The smell of freshly brewed coffee / Source: Istock.com/PuwanaiSomwan

Consequences of anosmia
Anosmia can have practical, social and psychological consequences. If you can no longer smell spoiled food or detect a gas leak, and you have no idea whether your clothes still smell fresh or need to be washed, you can imagine that this can make someone very insecure, especially in social situations. The ability to perceive smells and assign them a certain meaning also has an important psychological value. The smell of freshly mown grass, the smell of a summer rain after a sweltering day, the smell of a pine forest, the smell of freshly brewed coffee, the smell of our loved one, the smell that evokes a certain memory: all these things give it life an extra dimension. And don’t forget the smell of your meal. Complete loss of smell can cause a person to lose interest in food, which can lead to weight loss and malnutrition. Loss of smell has a lasting negative impact on the general quality of life. Anosmia can therefore also lead to depression and mood swings.

Causes partial or total loss of smell

The sense of smell can be affected by roughly the following three factors:

  1. changes in the nose;
  2. changes (or damage) in the nerves that run from the nose to the brain; or
  3. changes (or damage) in the brain.

Ad 1: A change in the nasal passage, for example because it is blocked as a result of a cold, can reduce the sense of smell because the smell is captured by the olfactory cilia cells at the top of the nasal cavity. Due to a blockage of (part of) the nose, the odorants can no longer properly reach the olfactory organ.
Ad 2 and 3: As a result of damage to the nerve pathway or part of the brain involved in smell, an olfactory disorder occurs.

No longer smelling anything due to a cold / Source: Istock.com/gpointstudio

No longer smelling anything due to a cold or flu

A viral upper respiratory infection due to a cold or flu is the most common cause of (partial) loss of smell. Some people cannot smell or taste properly for several days or even weeks after having the flu or a bad cold. This is a temporary loss of smell, which will disappear on its own. The culprit is often the parainfluenza virus type 3. Loss of smell after an upper respiratory infection is referred to as ‘post-viral anosmia’.

Permanent nasal congestion

With permanent blockage of the nose, the sense of smell may be affected for a long time or permanently. This can be caused, among other things, by:

  • nasal polyps;
  • chronic sinusitis or sinusitis;
  • allergic rhinitis;
  • severe obliquity of the nasal septum; and
  • large turbinates.


Surgery, trauma, smoking and cocaine

In some cases, paranasal sinus surgery can lead to a loss of smell due to damage to the olfactory epithelium. Some medicines and toxic substances can cause smell disorders. Smoking also has a harmful effect on the sense of smell, as does snorting cocaine. In people who stop smoking, their sense of smell eventually recovers. Head injuries (skull trauma) are another common cause of loss of smell, especially after a fall or a hard blow to the back of the head.

Medication can have a reduced sense of smell as a side effect / Source: Jarmoluk, Pixabay

Smell reduced by medicines

At least 250 different medications affect the sense of taste or smell, and some of these medications can cause hyposmia. This may include the following medications:

  • Antibiotics, such as ampicillin and tetracycline;
  • Antidepressants, such as amitriptyline; and
  • Antihistamines, such as loratadine.


Systemic diseases

Olfactory disorders can also occur in systemic diseases such as hypothyroidism (a deficiency of thyroid hormones), Cushing’s disease, severe liver failure, chronic renal failure and diabetes. Olfactory disorders are also seen in several psychiatric conditions, such as depression and schizophrenia. Parkinson’s and Alzheimer’s patients often exhibit smell disorders in the early stages of the disease. Loss of smell also occurs with HIV infection and hepatitis C infection and is mainly caused by damage and loss of olfactory epithelium.

Anosmia as part of a syndrome

Anosmia can be congenital and part of Kallmann syndrome. This is a congenital defect characterized by (almost) complete absence of smell, underdeveloped genitalia and sterile gonads. Familial anosmia also occurs, without other abnormalities.

Reduced sense of smell or taste due to a vitamin A deficiency / Source: Istock.com/NatchaS

Vitamin or mineral deficiency

A vitamin-mineral deficiency can also be the cause of a poor sense of smell and/or taste. One of the symptoms of a vitamin A deficiency and a zinc deficiency is a poor sense of smell and/or taste. Zinc is involved in all kinds of physiological processes in the body, including a good sense of taste and smell.


Furthermore, the sense of smell decreases with age. This is clearly noticeable, especially after the age of sixty. Loss of smell due to aging is called ‘presbyanosmia’. Some degree of loss of smell can be observed in 1 in 4 people over the age of 53.

No underlying cause

In roughly 20% of cases, no underlying cause for the loss of smell is found. This is called an idiopathic olfactory disorder. Idiopathic means ‘without demonstrable cause’.

Loss of smell due to nasal spray

If you have a short cold, you can safely use Otrivin nasal spray for a short time, but no more than seven days (see package leaflet), but preferably shorter. After a while, the blood vessels in the nasal mucosa become accustomed to the substance xylometazoline in the nasal spray. When administration of the substance is stopped, the blood vessels in the nose have to get used to the absence, causing them to dilate again. Long-term use of this nasal spray can even lead to damage to the nasal mucosa and it is even possible that the epithelium within the nose completely disappears. Although this can recover, it often takes many months before it is completely healed. The nose can remain closed for months after stopping the nasal spray and this also affects your sense of smell, making it difficult to continue.


Course of hyposmia

Hyposmia often improves without treatment, especially if it is caused by seasonal allergies or a respiratory infection. A person who notices a loss of smell when he or she has a cold or sinus infection usually regains their normal sense of smell within a few days or weeks. When hyposmia is caused by head injury or significant inflammatory damage to the cells involved in odor formation, recovery may not be possible even after treatment.

General practitioner with patient / Source: Istock.com/monkeybusinessimages

Examination and diagnosis

Interview and physical examination

Consult your doctor if you suddenly lose your sense of smell or if you have serious additional problems and complaints. The doctor starts with an extensive interview about the nature and severity of your complaints. This is called ‘anamnesis’. He will also review your medical history. The doctor will then perform a physical examination, paying particular attention to the upper respiratory tract. Your doctor will look at the nasal passages, sinuses and surrounding structure.

Follow-up research

If necessary, your GP can refer you to an ear, nose and throat specialist (ENT specialist). This specialist performs a nasal endoscopy, in which your nasal cavity and sinuses are examined with a thin flexible or rigid endoscope. For example, it is checked whether there are indications of chronic sinusitis or sinusitis. The doctor will look for signs of swelling, bleeding, pus, and possible tumors. The doctor will also look for other physical abnormalities that may be related to the loss of your sense of smell, such as (nasal) polyps, enlarged nasal structures or a deviated nasal septum. If this examination does not yield any results, an MRI scan of the brain can be done to detect neurological problems that may be responsible for the (partial) loss of the sense of smell. If necessary, a CT scan of the paranasal sinuses is also performed. Additional blood tests are only done if necessary.

Smell tests

The ENT doctor can measure the degree of smell loss using smell tests, so that the quality of the sense of smell can be objectified. Three types of smell tests are distinguished:

  • Identification tests, where you try to recognize test odors;
  • Threshold value tests, in which the minimum detectable concentration of a specific odorant is determined;
  • Discrimination tests, which examine whether you can distinguish between different odorants.


Restoration of sense of smell and possible treatment

Loss of sense of smell due to colds, allergies, or sinus infections usually recovers after a few days. Sometimes recovery takes several weeks. If no recovery occurs, consult your GP so that he or she can rule out other conditions.

Treatment and spontaneous course

The treatment options for olfactory disorders depend on the nature of the disorder and sometimes there is a spontaneous course. For example, an olfactory disorder caused by trauma can disappear on its own within a year in some cases. Some medications such as corticosteroids (anti-inflammatories) and antihistamines (an antihistamine suppresses allergic reactions) treat allergies or respiratory infections. A decongestant can also provide a solution. This medicine shrinks swollen mucous membranes and the doctor can prescribe it to open the nasal passages in case of a respiratory infection. In some cases, surgery is necessary to regain the sense of smell, for example with nasal polyps, a deviated nasal septum or other nasal problems that cause loss of smell.

Nasal polyps / Source: MathieuMD , Wikimedia Commons (CC BY-SA-3.0)

Conductive and sensorineural olfactory disorders

A distinction is often made between conductive (in case of blockage) and sensorineural olfactory disorders (the sense of smell or the olfactory nervous system is affected). Perceptual olfactory disorders are in turn distinguished into essential and central olfactory disorders: in an essential olfactory disorder the olfactory epithelium is damaged and in a central olfactory disorder there is damage in the course of the nerve pathway or part of the brain involved in smell. As of 2023, there is no effective treatment for perceptive smell disorders. Conductive olfactory disorders often improve by treating the blockage with medication or surgery. Especially in nasal polyps and chronic sinusitis, an improvement in smell is often seen after adequate treatment. Unfortunately, this effect is not always permanent. In some people with chronic sinusitis and nasal polyps, after an initial improvement in their sense of smell, their sense of smell will deteriorate again within a year after treatment.

Acceptance and self-help groups

If there are no treatment options, the loss of smell will have to be accepted as a disability and dealt with as best as possible. This is easier said than done, especially when the loss of smell is total. Understanding from the environment and contact with fellow sufferers can help with this. For example, there is an active patient association for people with smell and taste disorders: Anosmia Association Netherlands. This association has its own website (www.ruikenenstromen.nl).

Complications of loss of sense of smell

People with anosmia may lose interest in food and nutrition, leading to malnutrition and weight loss. People with anosmia should attach functioning smoke alarms in their home at all times. They must also be careful with food storage and the use of natural gas because they have difficulty detecting rotten food and gas leaks. Recommended precautions include:

  • Properly labeling foods with expiration dates;
  • Read labels and inserts on chemicals such as kitchen cleaners and insecticides;
  • Use of electrical appliances.


Prognosis of loss of smell

Loss of smell is usually caused by an upper respiratory infection or head trauma. Head trauma patients with mild or severe loss of smell have the same chance of functional recovery as patients with mild or severe loss of smell due to other causes. In other words, it is the extent of the initial loss of smell that is important, not what caused it. The literature reveals a number of factors that influence the prognosis. For example, the chance of recovery is better if the initial loss of smell is mild and unfavorable if the loss of smell is severe. Another factor is age: the older you were when the loss of smell occurred, the less likely it is that recovery will occur. The chance of improvement decreases considerably after the age of seventy.

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