Smell training involves sniffing at least four different odours, twice daily for several months.
Smell loss expert Prof Carl Philpott, from the University of East Anglia's Norwich Medical School, said that the method "aims to help recovery based on neuroplasticity - the brain's ability to reorganise itself to compensate for a change or injury".
Research by an international group of smell experts, published in the journal International Forum of Allergy & Rhinology, advised against using steroids to treat smell loss.
Prof Philpott said there is "very little evidence" they will help with smell loss and they have "potential side effects including fluid retention, high blood pressure, and problems with mood swings and behaviour".
He said Covid-19 has led to a "huge rise" in smell loss globally and around one in five people who experience smell loss as a result of coronavirus report that their sense of smell has not returned to normal eight weeks after falling ill.
"Luckily most people who experience smell loss as a result of Covid-19 will regain their sense of smell spontaneously," he said.
"Research shows that 90% of people will have fully recovered their sense of smell after six months.
"But we do know that smell training could be helpful.
"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.
"It aims to help recovery based on neuroplasticity, the brain's ability to reorganise itself to compensate for a change or injury."
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