UK Edition
Smell loss: the hidden but very common coronavirus symptom
The sudden loss of smell which many are experiencing could tell us a lot about how Covid-19 works
By now you will probably be well aware that a cough, shortness of breath or high temperature are warning signs of Covid-19, and anyone who gets them needs to self-isolate for seven days. But another odd symptom seems to be a calling card: a sudden loss of smell, which is not caused by a blocked nose.
The symptom appears to be incredibly common even though it is not yet widely discussed in the UK. More than two-thirds of those with coronavirus in Germany have lost their sense of smell, and 30 per cent of sufferers in South Korea have had anosmia as their main symptom, according to a report from ENT UK, an organisation which represents ear, nose and throat surgeons.
The smell loss associated with coronavirus is different to that which you might get with a normal cold, says Professor Claire Hopkins, president of the British Rhinological Society. “Typically when you have a cold your nose is congested, and therefore no-one is surprised you can’t smell”, she says. “But what’s happening here is there is no nasal obstruction so people are really surprised.”
The best guess of experts so far seems to be that Covid-19 is affecting the smell nerves in the nose. “We have seen evidence showing how the virus has the ability to affect the nerves, and the smell nerves are the only bits that are exposed in a way that no other nerves are”, says Professor Carl Philpott, professor of rhinology at the University of East Anglia. He believes that the virus causes neuronitis, or inflammation of the nerves in the nose, which stops them from performing as they should.
Professor Hopkins adds that the virus could even enter into the brain and cause further effects on the sense of smell, although this is not necessarily something to worry about: “Viral invasion is common but it sounds worse than it is.” She says that many rhinoviruses and coronaviruses which cause the common cold do this.
But no-one is yet completely sure for the reasons for the smell loss. Doing further research at present is difficult, says Professor Philpott: “We would need to examine the noses, and that’s what we’re telling people not to do as it puts the doctor at massive risk.”
Worryingly, anosmia can appear entirely by itself and without the “typical” coronavirus symptoms, which means that many will not be aware that they have it. This seems to be fairly common: in a study of suspected coronavirus-sufferers with smell loss, 1 in 6 had it as the only symptom, according to Professor Hopkins.
A further 1 in 10 lost their sense of smell before getting other symptoms, which shows that they could be spreading infection before reaching the criteria which require self-isolation. Professor Hopkins has seen this in her own life: “A colleague contacted me to say he lost his sense of smell 48 hours before. He got a private test which was positive, which meant he could stay away and not infect patients”.
Anosmia appearing without other symptoms is something we should be aware of, says Professor Nirmal Kumar, president of ENT UK. “The spreading of it is difficult because these patients aren’t terribly unwell, so they are walking around as if nothing is wrong”, he says.
This seems to be particularly the case when younger people catch Covid-19: “I saw nine young people with loss of sense of smell who were otherwise fit and well this month. That’s extremely unusual, I might usually see one a month”, says Professor Hopkins.
Some patients who are reporting smell loss are also saying that they have lost their ability to taste. The likelihood is they are mistaking smell for taste, says Professor Philpott. “When you’re eating 80 per cent of what you appreciate of flavour is the smell, so people think they can’t taste even though they can still get salty, sweet, bitter and sour.”
Some patients are even experiencing dysgeusia: things tasting different to normal. Most people suffering this are describing a “metallic taste”, says Professor Hopkins. “That does suggest other neurological manifestations as you should retain sweet, salty and so on. It suggests there is something going on in your brain potentially.”
The good news is that the coronavirus-induced anosmia looks like it will be temporary; most patients who have reported it so far describe their sense of smell returning within a fortnight says Professor Hopkins.
It could be that smell loss is not the only symptom of coronavirus that the UK is not yet picking up on. Many other countries are not focusing as narrowly on cough and temperature as we are: France’s diagnostic test asks 23 questions which cover sore throat, tiredness and aches, as well as loss of smell and taste. Professor Hopkins has seen some more unusual symptoms herself: “I’ve had a couple of colleagues say they had hearing loss or a burning sensation in their nose.”
The most important thing is to take smell loss seriously as a potential symptom of coronavirus. If you have suddenly lost your sense of smell, you should follow the recommendations for those with a new cough or temperature, says Professor Kumar, and isolate yourself for at least seven days. “For social distancing to work we need to make sure people are not spreading it around”, he says.