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Altered sense of smell common, even prior to COVID-19
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Altered sense of smell common, even prior to COVID-19

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Doctors are worried about a growing number of COVID-19 survivors who still don't have a sense of taste or smell. It's a common symptom that for many goes away with the virus, but for others it has stuck around months later. Researchers are still trying to figure out why it affects people differently. A doctor with Washington University School of Medicine predicts there will be at least 1 million new cases of people with chronically diminished senses in the coming year.

Q: What can cause someone to smell something bad, like heavy cigarette smoke or old garbage, when neither is nearby? And why does it make some foods taste funny when it happens?

A: Having an altered sense of smell is actually quite common. A survey of American adults found that two-thirds had experienced a problem with smell sometime during their lives. Smell disorders are often classified as one of the following:

• Anosmia: complete loss of the ability to detect odor.

• Hyposmia: decreased sense of smell with some ability to detect odors.

• Dysosmia: distorted sense of smell.

Altered smell common, even prior to COVID-19

Having an altered sense of smell is actually quite common.

Hyposmia commonly happens as we age. But what you describe falls under the category of dysosmia. With dysosmia, the distorted smell may be dramatically different from what you expect (known as parosmia). Or it could be an odor that isn’t actually present (known as phantosmia).

Your symptoms suggest you have periods of phantosmia: your brain registers an odor when none is present in the environment. But at other times, it could be parosmia, meaning you are more sensitive to a smell that doesn’t bother other people. When this occurs, the odor is usually described as unpleasant.

As to what might cause dysosmia, there are several possibilities. Today, COVID-19 tops the list, although it more often causes anosmia or hyposmia. Prior to COVID-19, potential causes included other viral illnesses, sinus infections, hay fever (allergic rhinitis), a medication side effect or a micronutrient deficiency. Some people experience dysosmia after general anesthesia.

Regarding food having a funny taste, our ability to fully enjoy food requires stimulation of many nerve endings in the mouth and nose. The strict definition of taste is the mouth’s ability to identify what is salty, sweet, sour, or bitter. There’s also a fifth, savory taste called umami (from the Japanese for delicious), which is triggered by the amino acid glutamate.

But what we commonly refer to as taste is actually a food’s flavor. Flavor is determined more by the food’s aroma, which is a function of our sense of smell rather than pure taste. So it makes sense that your dysosmia also interferes with the flavor of certain foods.

For most people who experience dysosmia, it’s a temporary alteration in sense of smell, often without an identifiable reason. However, if it becomes persistent, speak with your doctor. He or she will likely refer you to an ear, nose, and throat specialist.

Howard LeWine, M.D., is an internist at Brigham and Women’s Hospital in Boston and assistant professor at Harvard Medical School. For additional consumer health information, please visit www.health.harvard.edu.

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