What are olfactory disorders? What are the causes of dysosmia (a distortion in thesense of smell) and why do they occur? Why is this so important?
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Olfaction and the Importance of Our Sense of Smell
It would be hard to imagine living life without experiencing the smell of a rose, or the taste of morning coffee. Olfaction, our sense of smell, plays a significant role in almost everyone’s life.
Not only does olfaction help us detect fragrances in the air around us, but it’s also important in helping us enjoy the flavors of foods. You may have heard that “taste” primarily smells, and that is true to a large degree. A damaged sense of olfaction is severely disrupting: the joy of eating and drinking may be lost, and depression may result. Furthermore, there are dangers associated with theloss of smell, including the inability to detect leaking gas or spoiled food.
More than 2.7 million people in the United States have an olfactory disorder, and this is likely an underestimate. Some people have suggested that about half of people over the age of 60 have a decreased sense of smell.
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The Anatomy and Physiology of Olfaction (The Sense of Smell)
In the upper and middle part of the nose, there’s a small cell area called the olfactory mucosa. This area secretes several protective substances, like immunoglobulins (antibodies that bind with foreign matter such as microorganisms), in order to prevent pathogens from entering the head. There are also a large number of proteins, called receptors, that capture chemicals in the environment, or odorants. Each receptor is thought to have a special shape that fits these odorants like a key fits a lock.
The olfactory receptors live on an estimated six to ten million olfactory chemoreceptor cells in each nasal cavity. New receptors are formed throughout adulthood—one of the few examples of how the brain can form new nerve cells throughout life. When there’s a fit between an environmental chemical and a receptor on an olfactory cell, the nerve cell fires a signal directly to the brain on the olfactory bulb.
While the olfactory bulb is commonly considered the “firstcranial nerve,” it is technically not a nerve, but part of the brain itself. Signals transmitted from the olfactory bulb travel to special parts of the cerebral cortex and even the amygdala, which is a part of the brain involved with emotion. From the primary olfactory cortex, signals are relayed to other parts of the brain, including the thalamus and hypothalamus.
Smell Disorders
There are several terms that are used to describe the different types of smell disorders. These include:
Causes of Dysomia (A Distortion in the Sense of Smell)
There are a variety of factors and conditions that can cause dysosmia.
Other possible causes include:
The sense of smell is also commonly diminished through both natural aging, and in degenerative diseases like dementia. While the adult olfactory bulb in young adults has about 60,000 mitral neurons, both the number of mitral neurons and the diameter of their nuclei decrease dramatically with age.
In roughly one out of five people with olfactory disorders, the cause is “idiopathic,” meaning no specific cause is found.
Diagnosis of Olfactory Disorders
The diagnosis of olfactory disorders often begins with a careful history and physical exam. A physical exam can look for evidence of a viral infection or nasal polyps. A careful history may reveal possible toxic exposures.
A test known as the University of Pennsylvania Smell Identification Test may be done do assess whetherhyperosmiaor anosmia is truly present. Since there are many possible causes ranging from brain disorders to nutritional causes, and more, further testing will depend on many factors.
Treatment and Coping With the Loss of a Sense of Smell
There are not any specific treatments which can reverse a change in the sense of smell. Sometimes, dysomia resolves on its own in time. Researchers have evaluated the use of high dose vitamin A andzinc supplementation, but as of yet, this does not appear to be effective. Olfactory training is currently being evaluated and appears to be promising in early studies.
Coping is thus the primary goal of treatment. For those who have no sense of smell, safety measures such as making sure you have a fire alarm are important. Nutritional counseling may be helpful since some foods and spices which are most likely to stimulate the receptors (trigeminal and olfactory chemoreceptors.)
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Bottom Line on Olfaction and Disorders Which Affect Our Sense of Smell
1 SourceVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Xu X, Geng L, Chen C, et al.Olfactory impairment in patients with primary Sjogren’s syndrome and its correlation with organ involvement and immunological abnormalities.Arthritis Res Ther. 2021;23(1):250. doi:10.1186/s13075-021-02624-6Additional ReadingKasper, Dennis L.., Anthony S. Fauci, and Stephen L. Hauser. Harrison’s Principles of Internal Medicine. New York: Mc Graw-Hill Education, 2015. Print.Pekala, K., Chandra, R., and J. Turner.Efficacy of Olfactory Training in Patients with Olfactory Loss: A Systematic Review and Meta-Analysis.International Forum of Allergy and Rhinology. 2016. 6(3):299-307.Wongrakpanich, S., Petchlorlian, A., and A. Rosenzweig.Sensorineural Organs Dysfunction and Cognitive Decline: A Review Article.Aging and Disease. 2016. 7(6):763-769.
1 Source
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Xu X, Geng L, Chen C, et al.Olfactory impairment in patients with primary Sjogren’s syndrome and its correlation with organ involvement and immunological abnormalities.Arthritis Res Ther. 2021;23(1):250. doi:10.1186/s13075-021-02624-6Additional ReadingKasper, Dennis L.., Anthony S. Fauci, and Stephen L. Hauser. Harrison’s Principles of Internal Medicine. New York: Mc Graw-Hill Education, 2015. Print.Pekala, K., Chandra, R., and J. Turner.Efficacy of Olfactory Training in Patients with Olfactory Loss: A Systematic Review and Meta-Analysis.International Forum of Allergy and Rhinology. 2016. 6(3):299-307.Wongrakpanich, S., Petchlorlian, A., and A. Rosenzweig.Sensorineural Organs Dysfunction and Cognitive Decline: A Review Article.Aging and Disease. 2016. 7(6):763-769.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Xu X, Geng L, Chen C, et al.Olfactory impairment in patients with primary Sjogren’s syndrome and its correlation with organ involvement and immunological abnormalities.Arthritis Res Ther. 2021;23(1):250. doi:10.1186/s13075-021-02624-6
Kasper, Dennis L.., Anthony S. Fauci, and Stephen L. Hauser. Harrison’s Principles of Internal Medicine. New York: Mc Graw-Hill Education, 2015. Print.Pekala, K., Chandra, R., and J. Turner.Efficacy of Olfactory Training in Patients with Olfactory Loss: A Systematic Review and Meta-Analysis.International Forum of Allergy and Rhinology. 2016. 6(3):299-307.Wongrakpanich, S., Petchlorlian, A., and A. Rosenzweig.Sensorineural Organs Dysfunction and Cognitive Decline: A Review Article.Aging and Disease. 2016. 7(6):763-769.
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