Anosmia is a condition characterized by a loss of smell. While the condition can be temporary—such as in the case of severe nasal congestion due to a cold, allergy, or sinus infection—sometimes anosmia is a sign that something more is going on. Therefore, it's important to see a doctor if your sense of smell fails to return to normal as your other sinus symptoms improve. Your primary care provider may refer you to an ear nose and throat doctor (ENT) to diagnose the underlying cause.
Normal Aging Process
Just like vision and hearing, your sense of smell can diminish as you get older. If an ENT specialist determines that age is the cause, anosmia (known as presbyosmia in this case) may not be treatable.
The combination of less mucus production and the loss of nerve endings in the nose as you age can affect your ability to smell. When mucus production decreases, smells don't remain in your nose long enough for the nerve endings in the moist surfaces to detect them. This can change the way you perceive smells.
Aging and Medications
Certain medications, such as anti-inflammatory drugs, heart medications, and antidepressants, that doctors prescribe to treat age-related illnesses can cause loss of smell as a side effect. In some cases, reducing the dose or substituting another medication may help restore some of your ability to smell.
Aging and Progressive Disease
Chronic, progressive diseases such as Parkinson's disease and Alzheimer's disease, which are commonly associated with aging, can also affect your sense of smell. Alzheimer's disease can affect the olfactory cortex in the brain which processes smells; therefore the loss of smell may be an early sign of Alzheimer's disease.
A reduced sense of smell may be an early symptom of Parkinson's disease as well. Recent research suggests that the disease may have its origins in the gastrointestinal and olfactory systems before the protein clumps associated with the disease travel to other parts of the brain.
Smoking dulls the senses, including the senses of taste and smell. Smoking damages the olfactory nerve—a cranial nerve that plays a key role in the sense of smell—impairing your ability to smell.
An ENT doctor may insert an endoscope into your nasal passages to evaluate the extent of the damage smoking has caused to the nerves in your nose. Although your sense of smell may return after you quit smoking, heavy and long-term smoking can cause permanent damage whether you are young or old.
If the cause of your anosmia is nasal polyposis, you may need surgery to remove the polyps blocking one or both of your nasal passages. Polyps in the nasal cavity are small, noncancerous growths that can prevent smells from reaching the olfactory mucosa where signals are carried from olfactory nerve fibers to the brain. Allergies and recurrent sinus infections often trigger nasal polyps.
Removing these benign obstructions that block the air flow through nasal passages can restore your sense of smell. However, if inflammation of tissue high in the nasal cavity also occurs, you can suffer permanent damage and surgery may not help to restore your sense of smell.