Introduction
Smelling, or olfaction, is an important job of the nose. It’s not just about detecting scents and odors but also plays a role in how we behave, think, and enjoy life. Smell is vital for warning us about dangers, like the smell of fire, smoke, or a gas leak. It helps us avoid eating spoiled food and is linked to about 80% of what we taste. Remember the smell of a loved one or the taste of mom’s cooking? Smell and taste connect to our most profound memories and how we see the world. Losing these senses can be very difficult and can make life less enjoyable.
How Smell and Taste are Connected
When people say they’ve lost their sense of taste, it’s often because they’ve lost their sense of smell. The tongue helps us taste salty, sweet, sour, bitter, and savory (umami), but the most important flavor of food comes from our sense of smell. For example, the difference between chocolate and caramel is primarily due to smell. That’s why food doesn’t taste as good when you have a cold or a stuffy nose. While disorders of smell are common, affecting approximately 2 million Americans, true taste disorders are rare.
Where Smell Happens in the Nose
The nose has a special area high up called the olfactory cleft, which senses smell. Each side of the nose has its own olfactory cleft. Cells in this area can detect different smells in the air and send signals to the brain through the olfactory nerve.
Causes of Loss of Smell
Losing the sense of smell can happen because of a blockage in the nose (conductive) or damage to the olfactory cleft or nerve (sensorineural). Swelling from common colds, allergies, sinusitis, and nasal polyps can affect smell. Structural problems like a deviated septum or enlarged turbinates can also reduce smell. Nasal polyps are non-cancerous growths in the nose that result from inflammation and can commonly block smells. Inflammation from longstanding sinusitis can damage the cells and nerves involved in smell. It is important to not only treat the physical blockage but also the inflammation.
The common cold (See Upper Respiratory Infections) can also cause loss of smell. Usually, this is only for a few days or weeks. A few patients experience a more prolonged or permanent loss of smell after a cold. This permanent loss may be caused by inflammation and direct injury of the olfactory nerves by the viruses that cause the cold, such as COVID-19. Patients without an apparent reason for their loss of smell and taste likely have a viral-related loss of smell. They may not remember the inciting incident. The virus may have directly attacked the nerves themselves without causing other cold symptoms.
Zinc nasal sprays, previously used to prevent the flu, are associated with smell loss. Patients who have this type of loss describe an immediate burning sensation when using the spray, followed by a loss of smell. The Zicam brand of nasal spray has since been removed from shelves and is no longer available in the United States.
Loss of smell may also be linked to benign or malignant tumors, radiation treatment side effects, head trauma, aging, and health issues like obesity, diabetes, and neurological diseases like Parkinson’s, Alzheimer’s, and multiple sclerosis.
Testing for Loss of Smell
To determine why someone has lost their sense of smell, a doctor might use a nasal endoscope to examine the inside of the nose. A scratch-and-sniff test may also be used to measure smell loss. A CT or MRI scan can help identify abnormalities in the deep sinuses, olfactory system, and brain.
Treatments for Loss of Smell
Treatment of smell loss depends on the cause. Allergies or inflammation may be treated with antihistamines or steroids. Surgery could be an option for structural issues like a deviated septum, nasal polyps, or chronic rhinosinusitis. However, some causes, especially inflammatory diseases, may lead to permanent loss. Many patients with obstructive causes for their loss of smell report improvements after treatments. It is harder to predict recovery of smell after trauma or due to a virus. Medications, like oral steroids (prednisone), may help in some cases.
More recently, olfactory training has been helpful for patients with smell loss. Olfactory training, where the nose is exposed to strong smells several times per day, may stimulate the olfactory system and help recover smell, much like undergoing physical rehabilitation. Ongoing research aims to find more effective treatments over time.
Summary
If someone experiences loss of smell or taste, seeing a doctor is important. Early diagnosis helps determine the cause and potential treatments. While some losses are permanent, others can be improved with medical or surgical interventions, especially if started soon after the onset of loss.