What is anosmia

Anosmia is the medical term for complete loss of smell. You can be born with anosmia, but there are many things that can cause anosmia throughout life. If a person has a partial sense of smell, it’s called hyposmia. Many things – including smoking, a cold or flu, depression, schizophrenia, seasonal affective disorder and ageing – can cause hyposmia.

Anosmia may be temporary or permanent, depending on the cause. Although anosmia is rarely a symptom of a serious condition, even a partial loss of smell could cause you to lose interest in eating, which could possibly lead to weight loss, malnutrition or even depression.

Causes of anosmia include:

• head and nose injuries
• brain tumors and nasal polyps
• viral infections
• some chemicals
• some medications
• surgery
• Parkinson’s disease
• Alzheimer’s disease
• chronic sinusitis
• cocaine addiction

Some people never find out what caused them to lose their sense of smell.

If you have a cold or flu, your sense of smell will usually come back within a week or two. Otherwise, it’s a unpredictable – in some cases, anosmia can be permanent.

What is smell?

Smell results when individual molecules, suspended in the air, are inhaled and attach to receptors in the mucous membranes of the nose, stimulating nerves that connect directly to the brain. Any problem within this olfactory system — congestion or obstruction in the nose, inflammation of its lining, nerve damage, or altered brain function — affects your ability to smell normally.

While total loss of smell is fairly rare, and the more common causes improve with time, symptoms are sometimes severe enough to result in significant problems or distress. An intact sense of smell is necessary to accurately taste and enjoy food; losing this sense could cause you to lose interest in eating, potentially leading to weight loss, malnutrition or even depression.

Can anosmia be cured?

That depends on the cause of your anosmia. If you have a cold or flu, your sense of smell will usually come back within a week or two. Otherwise, it’s a unpredictable – in some cases, anosmia can be permanent.

Anosmia causes

The common cold with nasal congestion is the most common cause for a partial, temporary loss of smell. Obstruction in the nasal passages, particularly from polyps or nasal fractures, also is common. Normal aging also may cause a loss of smell, which may be progressive, becoming complete and permanent.

Causes of anosmia include:

• Allergies
• Head and nose injuries
• Brain tumors
• Blockage of the nose due to nasal polyps, nasal septal deformities, and nasal tumors
• Infections in nose, throat, or sinuses
• Viral infections
• Some chemicals
• Medicines that change or decrease the ability to detect odors (such as amphetamines, estrogen, naphazoline, phenothiazines, long-term use of nasal decongestants, reserpine, and possibly zinc-based products)
• Nasal or sinus surgery
• Parkinson’s disease
• Alzheimer’s disease
• Chronic sinusitis
• Cocaine addiction
• Endocrine disorders
• Dementia or other neurological problems
• Nutritional deficiencies
• Radiation therapy to head or face

Some people never find out what caused them to lose their sense of smell.

Problems with the inner lining of your nose

Conditions that cause temporary irritation or congestion of the mucous membranes lining the inside of your nose are the most common cause of loss of smell. These may include:

• Acute sinusitis (sinus infection)
• Common cold
• Hay fever (allergic rhinitis)
• Influenza (flu)
• Nonallergic rhinitis (chronic congestion or sneezing not related to allergies)

Obstructions of your nasal passages

Conditions or obstructions that block the flow of air through your nose can include:

• Bony deformity inside your nose
• Nasal polyps
• Tumors

Damage to your brain or nerves

Less commonly, the nerves leading to the olfactory center of the brain or to the brain itself can be damaged or deteriorate due to:

• Aging
• Alzheimer’s disease
• Brain aneurysm (a bulge in an artery in your brain)
• Brain surgery
• Brain tumor
• Chemical exposures to certain insecticides or solvents
• Diabetes
• Huntington’s disease
• Kallmann’s syndrome (a rare genetic condition)
• Klinefelter syndrome (a rare condition in which males have an extra X chromosome in most of their cells)
• Korsakoff’s psychosis (a brain disorder caused by the lack of thiamin)
• Malnutrition
• Medications (for example, some high blood pressure medications)
• Multiple sclerosis
• Multiple system atrophy (MSA) (a progressive disorder of the nervous system)
• Niemann-Pick (Pick’s disease, a form of dementia)
• Paget’s disease of bone (a disease that affects your bones, sometimes facial ones)
• Parkinson’s disease
• Radiation therapy
• Rhinoplasty
• Schizophrenia
• Sjogren’s syndrome (an inflammatory disease that generally causes dry mouth and eyes)
• Traumatic brain injury
• Zinc deficiency
• Zinc-containing nasal sprays (taken off the market in 2009)

Congenital anosmia

Congenital anosmia is a condition in which people are born with a lifelong inability to smell. It may occur as an isolated abnormality (no additional symptoms) or be associated with a specific genetic disorder (such as Kallmann syndrome or congenital insensitivity to pain) ¹. Isolated congenital anosmia is usually sporadic, although some familial cases have been reported. In most cases of isolated congenital anosmia, the genetic cause in unknown ². Unfortunately, there is currently no cure or treatment for congenital anosmia ³.

Studies suggest that approximately 1 in 10,000 people are affected by congenital anosmia ⁴. This includes people affected by isolated congenital anosmia (no additional symptoms) and those with congenital anosmia caused by a specific genetic disorder (such as Kallmann syndrome or congenital insensitivity to pain) ⁴.

What causes congenital anosmia?

Congenital anosmia may occur as an isolated abnormality or be associated with specific genetic disorders (such as Kallmann syndrome and congenital insensitivity to pain) ².

Most cases of isolated congenital anosmia (not associated with additional symptoms) occur sporadically in people with no family history of the condition. In these people, the exact underlying cause of the condition is unknown. Scientists suspect that the condition is due to abnormal development of the olfactory system (the sensory system used for sense of smell) prior to birth. This may include abnormalities of the nasal cavity; disruptions in the pathway that carries information from the nose to the brain; or malformations of the portion of the brain that processes sense of smell ².

When isolated congenital anosmia affects more than one family member, it may have a genetic component. One study found that some people affected by isolated congenital anosmia have changes (mutations) in the PROKR2 gene or PROK2 gene. These genes have previously been reported in people with Kallmann syndrome (an inherited condition associated with congenital anosmia and other symptoms) ⁴. Another study found that two brothers with anosmia had a mutation in the CNGA2 gene ⁵. However, in most familial cases of isolated congenital anosmia, the cause remains unknown.

Is congenital anosmia inherited?

Most cases of isolated congenital anosmia (not associated with additional symptoms) occur sporadically in people with no family history of the condition. Rarely, more than one family member may be affected. In these families, inheritance appears to be autosomal dominant with reduced penetrance ⁴. Autosomal dominant inheritance means that having a change (mutation) in only one copy of the responsible gene in each cell is enough to cause features of the condition. Reduced penetrance means that not all people who have or inherit the mutation will be affected. When a person with a mutation that causes an autosomal dominant condition has children (whether they are affected or not), each child has a 50% (1 in 2) chance to inherit that mutation. For conditions with reduced penetrance, it is not possible to predict whether a child who inherits the mutation will be affected. In most familial cases of isolated congenital anosmia, the genetic cause is unknown.

Congenital anosmia can also by associated with hereditary genetic disorders such as Kallmann syndrome and congenital insensitivity to pain. In these cases, it is inherited in the same manner as the associated condition. For example, Kallmann syndrome can be inherited in an autosomal dominant, autosomal recessive or X-linked recessive manner depending on the underlying genetic cause (it can be caused by mutations in several different genes) ⁶. Congenital insensitivity to pain has an autosomal recessive pattern of inheritance ⁷.

What is Kallmann syndrome

Kallmann syndrome is a condition characterized by delayed or absent puberty and an impaired sense of smell. Kallmann syndrome is a form of hypogonadotropic hypogonadism, which is a condition resulting from a lack of production of certain hormones that direct sexual development. These hormones are normally made in a part of the brain called the hypothalamus. Males born with hypogonadotropic hypogonadism often have an unusually small penis (micropenis) and undescended testes (cryptorchidism). At puberty, most affected individuals do not develop secondary sex characteristics, such as the growth of facial hair and deepening of the voice in males, the start of monthly periods (menstruation) and breast development in females, and a growth spurt in both sexes. Without treatment, most affected men and women are unable to have biological children (infertile).

In Kallmann syndrome, the sense of smell is either diminished (hyposmia) or completely absent (anosmia). This feature distinguishes Kallmann syndrome from most other forms of hypogonadotropic hypogonadism, which do not affect the sense of smell. Many people with Kallmann syndrome are not aware that they are unable to detect odors until the impairment is discovered through testing.

Kallmann syndrome can have a wide variety of additional signs and symptoms. These include a failure of one kidney to develop (unilateral renal agenesis), abnormalities of bones in the fingers or toes, a cleft lip with or without an opening in the roof of the mouth (a cleft palate), abnormal eye movements, hearing loss, and abnormalities of tooth development. Some affected individuals have a feature called bimanual synkinesis, in which the movements of one hand are mirrored by the other hand. Bimanual synkinesis can make it difficult to do tasks that require the hands to move separately, such as playing a musical instrument.

What is congenital insensitivity to pain

Congenital insensitivity to pain is a condition that inhibits the ability to perceive physical pain. From birth, affected individuals never feel pain in any part of their body when injured. People with this condition can feel the difference between sharp and dull and hot and cold, but cannot sense, for example, that a hot beverage is burning their tongue. This lack of pain awareness often leads to an accumulation of wounds, bruises, broken bones, and other health issues that may go undetected. Young children with congenital insensitivity to pain may have mouth or finger wounds due to repeated self-biting and may also experience multiple burn-related injuries. These repeated injuries often lead to a reduced life expectancy in people with congenital insensitivity to pain. Many people with congenital insensitivity to pain also have a complete loss of the sense of smell (anosmia).

Congenital insensitivity to pain is considered a form of peripheral neuropathy because it affects the peripheral nervous system, which connects the brain and spinal cord to muscles and to cells that detect sensations such as touch, smell, and pain.

What hereditary conditions are associated with congenital anosmia?

Isolated congenital anosmia, occurring with no other abnormalities, has been reported to run in some families (usually following autosomal dominant inheritance). In most of these cases, the underlying genetic cause is unknown. One study found that some people affected by isolated congenital anosmia have changes (mutations) in the PROKR2 gene or PROK2 gene. These genes have previously been reported in people with Kallmann syndrome, which is usually also associated with other features ⁴. Another study found that two brothers with anosmia had a mutation in the CNGA2 gene ⁵.

Congenital anosmia in combination with other abnormalities (syndromic anosmia) has been reported in various hereditary conditions, including ²:

• Kallmann syndrome – characterized by hypogonadotropic hypogonadism; anosmia or hyposmia (reduced ability to smell); and sometimes other abnormalities
• Congenital insensitivity to pain
• Some ciliopathies (diseases caused by defects in the function or structure of cilia) including Bardet-Biedl syndrome and Leber congenital amaurosis 10. These two disorders are characterized by retinal dystrophy and various other abnormalities.

People with multiple affected family members who have questions about the cause of anosmia in their family are encouraged to meet with a genetic counselor or other genetics professional. A genetics professional can help by:

• thoroughly evaluating the family history
• addressing questions and concerns
• assessing recurrence risks
• facilitating genetic testing if desired and available

The following online resources can also help you find a genetics professional in your community:

• The National Society of Genetic Counselors (https://www.nsgc.org/) provides a searchable directory of US and international genetic counseling services.
• The American College of Medical Genetics (https://www.acmg.net/) has a searchable database of US genetics clinics.
• The University of Kansas Medical Center (http://www.kumc.edu/gec/prof/genecntr.html) provides a list of US and international genetic centers, clinics, and departments.
• The American Society of Human Genetics (http://www.ashg.org/membership/member_search.shtml) maintains a database of its members, which includes individuals who live outside the United States. Visit the link to obtain a list of the geneticists in your country, some of whom may be researchers that do not provide medical care.

Congenital anosmia diagnosis

Isolated congenital anosmia (not associated with other symptoms) is a diagnosis of exclusion. This means that the diagnosis is made by ruling out all known conditions that may cause an absent sense of smell. When an affected person has no recollection of ever being able to smell, the following tests may be ordered to support a diagnosis of congenital anosmia ⁸:

• A thorough physical examination and medical history to look for other conditions that may interfere with sense of smell
• Smell tests, particularly those that determine the smallest amount of odor that someone can detect
• Brain Imaging (such as CT scan and MRI scan) to look for malformations in the portion of the brain that processes smell
• Nasal endoscopy to look for abnormalities of the nasal cavity which may interfere with sense of smell
• Olfactory nerve testing to evaluate disruptions in the pathway that carries information from the nose to the brain.

Congenital anosmia treatment

Unfortunately, there is currently no known cure or treatment for congenital anosmia ².

Anosmia prevention

Avoiding some chemicals and some drugs, and not smoking, might help prevent you losing your sense of smell.

Avoiding dangerous sports, like horse riding, and taking more care while driving, might reduce the chance of brain injury.

If you do have anosmia, you can make your environment safer by:

• making sure your smoke alarms are working
• checking that cookers, barbecues and electrical appliances are turned off properly
• reading food expiry dates carefully

Anosmia symptoms

Obviously, if you have anosmia, you can’t smell anything. But because the sense of smell is so closely connected to the sense of taste, you may find that food tastes bland. This can really affect your enjoyment of life, particularly if your social and family life revolves around meals. It can also make it hard for you to be bothered to eat and drink.

You might fear that you won’t be able to notice a dangerous smell, like gas or smoke. You might worry about eating something that’s spoiled. Some people living with anosmia can feel depressed.

Anosmia diagnosis

Your doctor might refer you to an ear, nose and throat specialist. Tell the specialist when and how you think you lost your sense of smell.

Your doctor will perform a physical exam and ask questions about your medical history and current symptoms.

Questions may include:

• When did this problem develop?
• Are all odors affected or only some? Is your sense of taste affected?
• Do you have cold or allergy symptoms?
• What medicines do you take?
• Do you have any other symptoms?

The specialist might examine you nose with a medical instrument called an endoscope. They might ask you to have a computed tomography (CT) scan or a magnetic image resonance (MRI) scan, or have a blood test.

Additional tests that may be performed include:

• Olfactory nerve testing
• Smell testing

Anosmia treatment

Treatment depends on why you lost your sense of smell. It can involve:

• nasal sprays and steroid pills
• antihistamines
• antibiotics
• an operation, e.g. to remove nasal polyps
• reducing your exposure to chemicals and other causes

You might get your sense of smell back without treatment, although it might take several weeks or months. Sometimes there is no treatment available.

There is no treatment for loss of smell due to aging.

If you have a loss of smell due to a recent upper respiratory infection, be patient. The sense of smell may return to normal without treatment.

If the loss of sense of smell is caused by a stuffy nose (nasal congestion), decongestants or antihistamines may be prescribed.

Other treatments for a stuffy nose may include:

• A vaporizer or humidifier may help keep mucus loose and moving.
• Steroid nasal sprays or pills may be recommended.
• Vitamin A may be given by mouth or as a shot.
• Nasal steroid sprays may be prescribed.

Avoid using too many nasal decongestants, which can lead to repeated nasal congestion.

If you lose your sense of smell, you may have changes in taste. Adding highly seasoned foods to your diet can help stimulate the taste sensations that you still have.

Improve your safety at home by using smoke detectors and electric appliances instead of gas ones. You may not be able to smell gas if there is a leak. Or, install equipment that detects gas fumes in the home. People with smell loss should label when the food item was opened to prevent eating spoiled food.

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5. Karstensen HG, Mang Y, Fark T, Hummel T, Tommerup N. The first mutation in CNGA2 in two brothers with anosmia. Clin Genet. September, 2015; 88(3):293-296. https://www.ncbi.nlm.nih.gov/pubmed/25156905[↩][↩]
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