Anosmia is the inability to smell. In fact, some people have anosmia from birth, whereas others lose their ability to smell over time.

Moreover, experts suggest that anosmia and hyposmia affect about 3–20% of the population. Hyposmia is a decreased ability to smell.

Additionally, sometimes people call anosmia smell blindness. Consequently, the condition may be permanent or temporary.

Furthermore, smell is a complex process that involves communication between the brain and nose. For instance, when a person sniffs an odor, air travels into the nose, and the odor molecules attach to receptors on the nerve that sense smell, called the olfactory nerve.

In this regard, these nerves line the olfactory epithelium, which is the tissue lining the nasal cavity. When this occurs, odor molecules from the environment stimulate these nerves, they transmit signals to the brain.

Finally, the brain receives the olfactory information and processes it into a scent that a person can identify.

What is Loss of Sense of Smell? -Anosmia

Symptoms

When people develop anosmia, they may notice that they can no longer smell identifiable odors. Conversely, people who were born with anosmia due to genetic differences may not recognize they have anosmia, since they never had the ability to smell.

Additionally, neurodegenerative diseases, such as Parkison’s disease and Alzheimer’s disease, may cause a loss of the sense of smell.

Therefore, if people living with neurodegenerative diseases recognize a loss of the sense of smell, they should seek medical evaluation as soon as possible. Indeed, sometimes anosmia is the earliest sign of neurodegenerative diseases.

Moreover, when a person can no longer smell, they are unable to sense warning odors in foods and the environment. As a result, people living with anosmia may experience a lower quality of life related to social interactions, eating, and feelings of well-being.

Causes

Several factors may contribute to anosmia, including:

  • First, chronic sinonasal diseases, which affect the nasal cavity or the nasal sinuses
  • Second, inherited anosmia
  • Next, neurodegenerative diseases
  • Moreover, older age
  • Furthermore, severe head injury
  • Finally, upper respiratory infections

Inherited Anosmia

Some people may inherit anosmia, which means they have it from birth. Consequently, healthcare professionals refer to anosmia not associated with any other condition as isolated congenital anosmia (ICA).

However, researchers have only identified two genes associated with ICA. Therefore, scientists need to do further research to find out more about the genetic basis for this condition.

Aging

As people age, their sense of smell decreases. Furthermore, people may also lose the ability to discriminate between different smells.

Experts suggest that possible reasons some older adults may lose their sense of smell include:

  • First, decreased nerve fibers and receptors in the olfactory bulb, a part of the brain responsible for processing scent
  • Second, loss of sensory cells in the nose
  • Lastly, deterioration in the central nervous system cognitive processing functions

Chronic Sinonasal Diseases

People with chronic sinonasal diseases may have one of two categories of disease: conductive or neurosensorial.

In particular, conductive sinonasal disease refers to conditions that affect airflow, such as:

  • Allergic rhinitis, or hay fever
  • Sinonasal tumors
  • Nasla Polyps
  • Septal deviation

On the other hand, people with neurosensorial sinonasal disease may have damage or dysfunction along the nerve pathway between the nose and brain. Specifically, some conditions that can damage this pathway include upper respiratory viral illnesses and toxin inhalation.

Furthermore, upper respiratory infection may contribute to 43% of neurosensorial olfactory loss. Similarly, tumors can also cause neurosensorial anosmia.

In addition, toxins that may contribute to anosmia include:

  • Tobacco
  • Illicit drugs
  • Toxic vapor

Neurodegenerative diseases

Moreover, some neurodegenerative diseases that may cause anosmia or some degree of loss of smell include:

Idiopathic Anosmia

Finally, sometimes doctors are unsure why a person developed anosmia. This is known as idiopathic anosmia.

Diagnosis

General health exams do not typically include olfactory or smell testing. Therefore, to detect whether a patient has anosmia, a doctor needs to rely on them to self-report a loss of or change in their ability to smell.
In general, experts suggest that self-reporting of the sense of smell is specific but not sensitive. Consequently, this means that people may not be able to recognize anosmia if they experience it.
Furthermore, improving health questionnaires may help doctors diagnose anosmia better.
In particular, diagnostic questionnaires may help identify more people with anosmia by asking both younger people and older adults about any changes they have experienced in their smelling ability and the presence of phantom scent sensations.
Additionally, the National Health and Nutrition Examination Survey (NHANES) self-reported olfactory function index offers a reliable method to screen for anosmia.
Ultimately, through this survey, doctors can arrange further examination for a person based on what they report.

Treatment

When deciding on the most appropriate treatment for a person living with anosmia, doctors must choose a therapy that matches the cause.
For instance, people with genetic disorders may want to look into treatment options, such as cell and genetic therapies.
On the other hand, if a person developed anosmia following an infection, doctors may suggest the supplement zinc gluconate or smell training.
Similarly, people with post-traumatic olfactory disorders resulting from a head injury may also benefit from smell training.
In fact, smell training involves sniffing four different odors intensely twice per day for several seconds over at least 4 months. Moreover, people may benefit more from this therapy when they sniff a variety of odors on rotation over a prolonged training period.
Conversely, surgery or corticosteroid drugs may be the only available options for people with anosmia resulting from sinonasal disorders. In this case, doctors may recommend corticosteroid drugs to manage anosmia, taken either into the nose or by mouth.
Furthermore, researchers have only shown that topical intranasal steroids are effective in allergic rhinitis, especially when a person takes them with intranasal antihistamine.
Lastly, oral corticosteroids can be effective for anosmia, although the dose and duration are still controversial.
Doctors may find it challenging to predict whether surgical methods can help with anosmia. Moreover, endoscopic sinus surgery might improve anosmia in some people.
Furthermore, some cases of anosmia may also resolve spontaneously without treatment. Specifically, this can occur in about 32–66% of patients with an upper respiratory tract infection.
In addition, some people living with anosmia report they have difficulty finding and receiving appropriate care for their condition.
Consequently, part of the issue is that some people living with anosmia have difficulty detecting, identifying, and distinguishing the condition.

Complications

People living with anosmia may experience, consequently, a lower quality of life. Losing the sense of smell can affect romantic and sexual intimacy because smelling one’s intimate partner is part of the sensual experience.
Furthermore, mealtime may also be less enjoyable, particularly when a person cannot smell their food.
In addition, anosmia can also be dangerous. Normally, a person’s sense of smell can inform them of environmental dangers, such as a gas leak or the presence of smoke. Moreover, the ability to smell spoiled food or poisonous liquids can prevent a person from accidentally ingesting toxins.
Finally, people living with Alzheimer’s or Parkinson’s disease may develop severe complications from anosmia, including malnutrition, safety problems, and increased mortality risk.

COVID Related Anosmia

“The novel coronavirus responsible for the COVID-19 pandemic causes, in particular, a reduction of smell and taste in many patients.
These symptoms occur early in the disease; moreover, they may sometimes be the only recognizable symptom in people with the SARS-CoV-2 virus.
In studies researchers did earlier in the COVID-19 pandemic, they reported that anosmia occurred in about  5% initially of individuals with a SARS-CoV-2 infection. However, further studies throughout the pandemic reported higher rates of anosmia.
A hypothesis for why some people with a SARS-CoV-2 infection develop anosmia is, in part, genetic differences that affect the ability of the virus to attach to receptors in the nasal cavity.
Consequently, this may dictate the infectivity and spreading of the virus. Therefore, researchers need to conduct further studies to investigate these findings.
If research can support this hypothesis, it may help clinicians better describe which populations are more at risk of developing COVID-19, and in turn may help healthcare experts manage the pandemic more effectively.
Ultimately, people with a SARS-CoV-2 infection typically regain their sense of taste and smell after several days or weeks; however, for some, it can take much longer than that.

Summary

Although losing the sense of smell, or developing anosmia, does not appear to be life threatening, the complications can, in fact, be dangerous.
Furthermore, smell allows people to recognize a dangerous environment or spoiled food; consequently, people living with anosmia lose this ability.
Additionally, smell also provides pleasure. For instance, smelling the scent of delicious food, the fresh air of the countryside, or the sensual scents of intimate moments enhances a person’s everyday experiences. As a result, people who recognize they have lost their sense of smell may experience a lower quality of life.
Moreover, doctors have identified several causes of anosmia. Notably, some causes can lead to permanent or temporary loss of smell. Therefore, choosing the most appropriate treatment requires an accurate diagnosis of the cause of anosmia.

Biospecimen

biospecimen

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Types of Biospecimens

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In addition to the standard processing protocols, Bay Biosciences can also provide human plasma, serum, and PBMC bio-fluid samples using custom processing protocols. Additionally you buy donor-specific collections in higher volumes and specified sample aliquots from us.

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