Why do Covid patients lose their sense of smell? Medics aim to explain symptom mystery

The study in Singapore looked into why some people with Covid-19 were more likely to experience an altered or reduced sense of smell

The study’s author said it is “good news” for those wanting to recover their sense of smell after having Covid-19 (Getty Images)

A new study could explain why some people lose their sense of smell when diagnosed with Covid-19.

The analysis by researchers in Singapore found that altered smell was 16 times more likely to happen to people with specific, pre-existing nasal abnormalities.

Loss or change to sense of smell is one of the most common and recognisable symptoms of coronavirus, alongside a new, continuous cough, a high temperature and altered taste.

The study discovered that people who lose their sense of smell when diagnosed with Covid-19 could have a nasal abnormality called a abnormal olfactory cleft.

The olfactory clefts are tunnels in the nose that help make us able to smell normally, and an altered or decreased sense of smell - or a olfactory dysfunction - was found to be more 16 times more common in those those with an olfactory cleft abnormality.

“Before this study, most scientists thought that the loss of smell in COVID-19 was mainly due to inflammation and damage to the olfactory nerves,” said senior author Neville Wei Yang Teo, MRCS, MMed, of Singapore General Hospital.

“Now, we have compiled evidence from medical imaging that COVID-19 loss of smell is also due to swelling and blockage of the passages in the nose that conduct smells.”

The peer-reviewed study by Wiley and published in the The Laryngoscope involved researchers analysing medical literature on changes in olfactory structures found through imaging tests of coronavirus patients.

It found that the prevalence of an olfactory cleft abnormality was nearly 16-fold higher in patients with Covid-19 and olfactory dysfunction (63%) compared with controls (4%).

“We think this is good news for patients who want to recover their sense of smell,” said lead author Claire Jing-Wen Tan, of the National University of Singapore, “since these blockages are expected to resolve with time, while nerve damage in comparison would likely be more difficult to recover from,”

“These findings may not fully account for those who suffer from prolonged olfactory dysfunction, however, and further studies that evaluate patients in this group may provide more information.”

Britain first recognised a loss of smell or taste as symptoms of Covid-19 in May 2020, months after its first reported case, and it is now one of the most recognisable symptoms of the virus.