- Even people with mild Covid-19 infections experience loss of smell and taste
- Some patients never entirely recover their sense of smell
- It's not a cure, but in some cases 'smell training' help people regain some of their olfactory ability
Since the start of the Covid-19 pandemic, it's become clear that many people with the infection lose their sense of smell and taste. And doctors are concerned that some will never get back to normal.
At this point, it's hard to know how common the symptom is. First, there were anecdotal reports of Covid-19 patients who had lost their ability to smell or taste, said Dr Nicholas Rowan, an assistant professor of otolaryngology-head and neck surgery at Johns Hopkins University in Baltimore.
And then, he said, studies started to confirm "there's a lot of truth to it".
Rowan pointed to one study of patients hospitalised for Covid-19 that used objective tests to detect smell "dysfunction". Nearly all patients – 98% – showed some loss of smell.
Smell and taste intertwined
But the problem isn't limited to severely ill patients. It appears to be common, and even a "cardinal" symptom, among people with milder Covid-19 infections. Cardinal symptoms are the key ones from which a diagnosis is made.
For example, in a study of European patients with mild-to-moderate Covid-19, 86% reported problems with their sense of smell, while a similar percentage had changes in taste perception.
As anyone who's ever had a cold knows, smell and taste are closely intertwined, Rowan said. So the loss of smell – which doctors call anosmia – may be diminishing people's perception of flavours.
But, Rowan noted, it's also possible the coronavirus does have some direct effect on the sense of taste.
Respiratory viruses, including cold viruses and the flu, are known to sometimes trigger anosmia.
Fortunately, the issue resolves for most people. "But unfortunately," Rowan said, "some patients are left with permanent olfactory [smell] dysfunction."
Infects area of olfactory nerve
That's what has doctors worried – particularly since these sensory problems appear unusually prevalent in people with Covid-19.
"It does happen with other viruses," said Dr Daniel Coelho, a professor of otolaryngology-head and neck surgery at Virginia Commonwealth University in Richmond.
"But," he added, "we're seeing it a heck of a lot more with this virus."
It's not clear why, but Rowan said there's some evidence that SARS-CoV-2 – the virus that causes Covid-19 – directly infects the area of the olfactory nerve. That might be how the virus gains entry into the body.
For some people, loss of smell and taste may be the first red flag that they are infected – or even the only symptom, both Rowan and Coelho said.
Coelho and his colleagues have undertaken a nationwide study to track changes in smell and taste related to Covid19. Preliminary results, based on 220 survey respondents, indicated that nearly 40% had loss of smell or taste as a first, or only, symptom of Covid-19.
For some, improvement has been slow.
"We're assuming that not all of these patients are going to return to their pre-Covid level of function," Coelho said.
And that's a concern, Rowan said. "There's a well-described correlation between anosmia and depression and anxiety," he noted.
Smell training supported
Correlation doesn't mean "cause-and-effect", he added. On the other hand, Rowan said, there's no doubt that much of the pleasure in life is related to the sense of smell – from enjoying meals to bonding with other people.
Coelho agreed that anosmia takes a toll on quality of life, and can even be dangerous – if a person can't smell the smoke from a house fire, for example. "We really tend to take our sense of smell for granted," he said.
As for treating lingering anosmia, the options are "not great", according to Rowan. But some evidence supports smell training, he said. It works like other types of rehabilitation, where a person relearns a diminished ability – in this case by spending time each day sniffing essential oils or other scents.
"It's not a cure, and it doesn't work for everyone," Rowan said. "But it's a viable option and basically no-risk."
As for people who develop a new problem with smelling ability, take it seriously, Rowan advised. "It might be the first sign of Covid-19," he said.
Coelho echoed that point. "Presume you're positive," he said. "Then self-isolate and call your doctor about what to do next."