Coronavirus: How does the infection dampen our taste and smell?
A loss to our sense of smell or taste is now recognised by the NHS as a key symptom of the coronavirus.
With Britons previously being told they only had to self-isolate entirely at home if they developed a fever or cough, muted senses has now been added to that list.
While the move was welcomed by experts, some worried it came a little too late.
The World Health Organization and US Centers for Disease Control and Prevention have long recognised a loss of taste or smell as a potential sign of infection.
Now Britons know to look out for the tell-tale symptom, it begs the question how the coronavirus could rob us of our senses, albeit temporarily.
Early research suggests the coronavirus is mild in four out of five cases, however, it can trigger a respiratory disease called COVID-19.
Coronavirus: How does it dampen our smell and taste?
The coronavirus is not the only infection that dampens our senses, with the seasonal sniffles also leaving many unable to taste their food.
Speaking to Stanford Medicine’s blog Scope, Dr Zara Patel explained viruses can “attack” the cranial nerves.
Some of these nerves “bring information from the sense organs to the brain”.
When the immune system detects an invading pathogen, like a virus, it launches an immune response that triggers inflammation.
This inflammation can affect the nerves in the nasal lining or the inner body of the nerves themselves, leaving them unable to function correctly.
The coronavirus only emerged at the end of 2019, with relatively little being known about how it operates.
Professor Myra McClure, from Imperial College London, wondered whether it has a “broader tropism than we first thought”, making it capable of infecting cells outside of the airways.
Even if the coronavirus does not just infect the respiratory tract, “it would not be difficult to understand why changes to the nasal tract caused by the virus could damage the ability to taste and smell”, she told Yahoo UK.
“The most likely explanation is – like [with] other respiratory viruses – the nasal passages become congested with excess mucous, nasal secretions and dead cell shedding, leading to the loss of smell.
“If you were to look microscopically at the specialised cells responsible for taste and smell, you would probably see the hair-like endings that detect odours have been damaged or destroyed as a result of the infection and can no longer able to pick up the molecules of smell.”
While no one can say for sure what mechanism is at play, a loss of taste and smell usually go together.
“Taste is so linked to smell that the loss of smell is also usually loss of taste,” Professor Paul Hunter, from the University of East Anglia, told Yahoo UK.
Coronavirus: Do taste and smell come back?
Most coronavirus sufferers are expected to recover their sense of taste and smell in full, however, it can take time.
“Once the swelling in the nasal passages has subsided and the virus comes under control within about 14 days, taste and smell usually returns with all respiratory viral infections”, said Prof McClure.
Professor Hunter warned, however, damage to the cells that pick up smell can persist for “several years”.
Nevertheless, most coronavirus patients recover their senses within 14 days, he agreed.
This suggests the symptom comes about due to “inflammation of the olfactory nerve rather than damage to the receptors”.
“We will need to wait to see whether some COVID-19 patients develop the more long lasting form,” said Prof Hunter.
Dr Patel recommended seeking help sooner rather than later if muted senses persist after other symptoms have passed.
“Olfactory training” and certain medications can help people smell the roses again, she added.
What is the coronavirus?
The coronavirus is one of seven strains of a virus class that are known to infect humans.
Others cause everything from the common cold to severe acute respiratory syndrome (Sars), which killed 774 people during its 2002/3 outbreak.
Since the coronavirus outbreak was identified, more than 5.4 million cases have been confirmed worldwide, according to Johns Hopkins University.
Of these cases, over 2.2 million are known to have “recovered”.
Globally, the death toll has exceeded 346,300.
The coronavirus mainly spreads face to face via infected droplets expelled in a cough or sneeze.
There is also evidence it is transmitted in faeces and can survive on surfaces.
Symptoms include fever, cough and slight breathlessness.
The coronavirus has no “set” treatment, with most patients naturally fighting off the infection.
Those requiring hospitalisation are given “supportive care”, like ventilation, while their immune system gets to work.
Officials urge people ward off infection by washing their hands regularly and maintaining social distancing.
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