Loss of smell can be devastating. One’s sense of smell is intimately related to the sense of taste, and so an alteration or loss of smell affects the ability to appreciate the quality of food and drink. A complete loss of smell is termed anosmia, whereas partial loss of smell is called hyoposmia.
Viral infections can cause this problem. Temporary loss of smell (and taste) is quite common with COVID-19 infections, but the majority of patients fully regain these senses. However, there are a minority who have persistent loss of, or reduced, sense of smell, long after the virus has cleared out. This also occurs—fortunately infrequently—with annual influenza virus (the “flu”) where damage to the nerves that provide for the sense of smell are permanently damaged.
Patients complain that, “I can’t smell a thing, even my dog’s poop!” or “things don’t smell right, some stuff smells foul, like dog poop” or “food has no taste,” or “some of it tastes nasty, like poop!” Notice the common denominator? “Poop” is synonymous with displeasure.
Brief anatomy primer
There are two “bulbs” just above the nasal passages, one on each side. These olfactory bulbs are comprised of too-many-to-count individual olfactory nerves that arise under the front part of the brain. Each bulb lies on top of the skull base above the nose called the cribiform plate. Tiny branches of the olfactory nerves then travel through small porous openings in the cribiform and then branch out into the mucosa of the upper part of the nasal cavity. As air moves into the nose, molecules of substances that carry any type of odor travels upwards to stimulate those nerves. The nerve signals are transmitted to the brain where it interprets the smell input. That input also is processed into taste sensation, which is the reason a sense of smell is required for a sense of taste.
The tongue also has nerves that sense taste. But these nerves only provide the 5 rudimentary tastes of sweet, sour, salt, bitter and unami (the “meaty” character of certain foods). Many patients with loss of smell can detect these basic tastes, but the real quality, the subtle nuances and the unique flavor of food is impaired or absent. Sometimes normally flavorful foods can have an unpleasant, rancid or foul taste for those with impaired smell. Hence, the pop comparison.
Those Bad Viruses
Let’s say we’ve ruled out treatable causes (such as nasal polyps, chronic sinusitis, nasal congestion from allergies, and the like) and you’re left with a post-viral cause. Once the virus clears your system and you’re no longer feeling ill, the inflammatory effects can still damage structures such as nerves. Sometimes the nerves recover and the sense of smell is restored. Sometimes they don’t. Viruses can wreak havok on other neuromotor or neurosensory areas, such as the case with Bell’s Palsy (facial nerve paralysis) and the inner ear in sudden hearing loss, both believed to be virally-caused.
In the case of prolonged loss of smell after viral infections such as the run-of-the-mill flu or COVID, there are no really no adequate medical therapies to restore the lost sense of smell. However, olfactory training can be of benefit to improve one’s sense of smell (and subsequently sense of taste, since these two senses go hand in hand). This is based on the concept of neuroplasticity, where nerves can form new connections when repeatedly stimulated. This is the basis of olfactory training. In the case of impaired smell, repeatedly smelling a variety of strong odors for a prolonged period of time can aid in neuroplasticity.
Instructions
for olfactory training:
Use
substances with strong scents, such as essential oils with highly concentrated
odors.
Sniff in at least four different scent types:
1. Flora (such as rose, lavender)
2. Citrus (i.e., lemon, orange)
3. Spice (such as clove, peppermint, rosemary)
4. Fresh or effervescent scents (i.e., eucalyptus)
Smell each scent for twenty seconds or more, twice a day for three months.
A couple studies have shown 21-26% of patients had a significant improvement after three months of this form treatment (vs 9% and 11% for their respective control groups). Yeah, I know these numbers aren’t great, but at least it’s a promising means of therapy to offer with little risk. It requires a bit of persistence over a considerable amount of time to extract any benefit. But it beats using the “poop” term repeatedly, which I imagine loses its novelty and becomes rather tiresome for those who must hear it over-and over-again (and wish they’d suffer sudden hearing loss…sorry, bad joke).
©Randall S. Fong, M.D.
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topics on medicine, health and the weirdness of life in general, check out the
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