"Smell training" could help coronavirus patients regain the lost sense after overcoming the infection, research suggests.
The coronavirus is thought to be mild in four out of five cases, however, even those who do not become seriously ill may experience lingering complications. Smell loss is relatively common, with around one in five still enduring the muted sense eight weeks after catching the infection.
Corticosteroids, often used as a preventative asthma treatment, have been suggested as a remedy for coronavirus-related smell loss.
A group of international scientists have urged "caution", however, with there being little evidence the drugs are effective.
The team instead recommends smell training – sniffing at least four different odours twice a day for several months.
"The huge rise in smell loss caused by COVID-19 [the disease caused by the coronavirus] has created an unprecedented worldwide demand for treatment," said study author Professor Carl Philpott, from the University of East Anglia.
"Around one in five people who experience smell loss as a result of COVID-19 report their sense of smell has not returned to normal eight weeks after falling ill.
"We do know smell training could be helpful.
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"This involves sniffing at least four different odours twice a day every day for several months.
"It has emerged as a cheap, simple and side-effect free treatment option for various causes of smell loss, including COVID-19."
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Coronavirus-related smell loss is thought to be caused by inflammation, which can be dampened by corticosteroids.
Nevertheless, the scientists have said evidence supporting this approach is "weak".
Corticosteroids also have "well-known potential adverse events", particularly when taken in tablet form, rather than as an inhaler.
"Doctors often prescribe them to help treat conditions such as asthma and they have been considered as a therapeutic option for smell loss caused by COVID-19," said Professor Philpott.
“They [the drugs] have well-known potential side effects including fluid retention, high blood pressure, and problems with mood swings and behaviour."
Writing in the journal International Forum of Allergy & Rhinology, the scientists also pointed out "spontaneous recovery" of smell in coronavirus survivors is "high".
"Luckily most people who experience smell loss as a result of COVID-19 will regain their sense of smell spontaneously," said Professor Philpott.
"Research shows 90% of people will have fully recovered their sense of smell after six months."
In the meantime, smell training helps "the brain's ability to reorganise itself to compensate for a change or injury".
The scientists have added corticosteroids may be useful when another cause of smell loss worsens the coronavirus' lingering effects, like chronic inflammation of the sinuses.
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