Disorders of Smell & Taste
Arthur Wu, MD
Remember the smell of your spouse’s perfume or cologne or the taste of your mother’s cooking? Taste and smell unlock some of our deepest memories. They are critical to our perception of the outside world, and the loss of taste and smell can be a deep blow to one’s quality of life.
The Relationship Between Taste and Smell
Most patients who complain of a loss of taste actually suffer from a loss of smell. The majority of a food’s flavor comes from our ability to smell it. The tongue is our taste organ, and it can only sense salty, sweet, sour, bitter, and umami (or savory). This is why it is difficult to appreciate a food’s flavor when one has a cold or stuffy nose. Disorders of smell and taste are fairly common, affecting approximately 2 million people in the United States. However, true disorders of only taste are quite rare.
The Anatomy of Smell
The part of the nose that senses smell is a very small area high up in the roof of the nose called the olfactory cleft. Each side of the nose has its own olfactory cleft, where special cells can sense the various odors carried in the air we breathe (Image 1). These cells send their signals to the brain via the smell or olfactory nerve.
Causes of Loss of Smell
Loss of smell can result from a physical blockage of the nose or from damage to the olfactory cleft or nerve. Patients with a deviated septum
or with allergies
may have nasal obstruction which prevents odors from getting to the olfactory cleft. Nasal polyps, small non-cancerous growths in the nose, can also block smells from entering the nose (Image 2). Very rarely, loss of smell can come from benign or malignant tumors
in the nose.
Chronic sinusitis also can cause loss of smell by obstructing the nose with inflammation and swelling, but it also can permanently affect smell by injuring the special cells and nerve of the smell pathway.
As mentioned before, the common cold
often causes inflammation in the nose impairing smell. Usually this loss of smell returns days to weeks after the initial illness has resolved, but a small number of patients experience a more prolonged or permanent loss of smell after a cold. Many patients without a clear reason for their loss of smell and taste likely have viral-related loss of smell but do not remember the inciting incident.
There has been an association between zinc nasal sprays, used to prevent or shorten flu or colds, and sudden and permanent smell loss. Patients who have had this type of loss describe immediate burning sensation when using the spray followed by loss of smell. The Zicam nasal spray has since been removed from shelves and is no longer available.
Trauma to the head as in a car accident can also cause injury to the brain or the olfactory nerves causing temporary or permanent smell loss. Importantly, sense of smell also diminishes with age in a similar fashion as vision and hearing.
Testing for Loss of Smell
The physician examining a patient for loss of smell will need to perform an exam of the inside of the nose, usually with nasal endoscopy
. The physician will be looking for a deviated septum, polyps, inflammation, or other causes for physical blockage of the olfactory cleft and sources of smell loss.
The physician may also use a scratch-and-sniff or other smelling test to quantify the amount of smell loss a patient has.
In the event that there is not an obvious reason for the loss of smell, a physician may order an MRI to evaluate the olfactory cleft, nerve, and brain for any abnormalities.
Treatments for Loss of Smell
If the physician determines a patient’s loss of smell to be caused by allergies or other inflammatory diseases, he/she may recommend nasal or oral steroids to decrease the inflammation. Surgery
may be suggested if the patient is found to have nasal polyps, chronic sinusitis
, deviated septum, or other surgically treatable disorders. As mentioned before, despite medical or surgical, sometimes permanent damage to the smelling apparatus has already been done and return of smell back to a totally normal state may not always be possible. Usually patients who have obstructive causes for their loss of smell do report significant improvements though.
Patients with a permanent loss of smell after a viral illness or those without a clear reason for their loss of smell unfortunately have limited treatment options. A short course of oral steroids may be beneficial in some patients and is a relatively harmless treatment even if ultimately unsuccessful. Research is ongoing to determine the cause and potential treatment for this type of smell loss.
Patients who suffer from smell or taste loss are encouraged to seek medical attention to determine the cause of their smell loss. While certain smell losses are permanent, others can be effectively treated medically or surgically by a nose and sinus specialist.
Image 1: During a nasal endoscopy, an otolaryngologist can see the olfactory cleft between the nasal septum and the middle turbinate (MT) in a normal patient.
Image 2: A patient with a polyp (P) between the septum and middle turbinate (MT) that is affecting smell. The surgeon is pointing to the polyp with a metal suction instrument during a surgery to remove the patient’s polyps.
©American Rhinologic Society