London (CNN) "I woke up and couldn't taste or smell anything. It was the most acute thing I've ever experienced," says Londoner Holly Bourne.

Bourne has not had the widely recognized coronavirus symptoms -- a cough or high fever -- and therefore is not eligible to be tested by the UK's National Health Service (NHS). But her experience of suddenly losing her sense of smell, combined with "weird head rushes," headaches and exhaustion led her doctor to diagnose her "straight off the bat" with Covid-19 over the phone.

While there have yet to be robust studies on the link between coronavirus and smell, doctors have reported anecdotally that losing the ability to smell may be among the virus's symptoms -- but how widespread that is, and how long it might last, is unclear.

"I feel lucky I don't have the really scary symptoms," the 33-year-old author says. However, she describes her loss of the sense of smell, or anosmia, as "one of the most upsetting things I've ever gone through because you're not in the driving seat.... I just feel really powerless and scared."

Aside from the psychological impact of believing you've caught a deadly virus, and how losing your sense of smell strips joy from eating food, anosmia can also be dangerous.

Holly Bourne describes her anosmia as "one of the most upsetting things I've ever gone through."

As Bourne discovered when her boyfriend asked why a plastic margarine tub was melting on the stove in their London home. She had her back turned while making sandwiches and couldn't detect the synthetic burning smell.

Like the dozens of people experiencing loss of smell that CNN has spoken to for this article, with a lack of official health authority advice available, Bourne turned to Google and social media for answers. She shared what she found in a thread on Twitter, where some people are reporting their sense of smell still hasn't returned after three or four weeks.

I'm making a thread for those who have lost their sense of smell and taste due to #COVID19 with all the things I've found helpful. It's an unnerving, miserable symptom and I know I've spent the last two weeks frantically googling it. Hope this is useful to you. Please add to it — Holly Bourne (@holly_bourneYA) April 6, 2020

The thing many people experiencing new-onset anosmia or hyposmia -- a partial smell loss -- during the coronavirus pandemic want to know is how long is it going to last? Will it be permanent?

The answer, according to Professor Steven Munger, Director of the University of Florida's Center for Smell and Taste, is unknown.

"What we've known for a long time is one of the major causes of smell loss are upper respiratory tract infections due to viruses -- a common cold, influenza -- a subset of people lose their sense of smell, most of them temporarily, but a small subset lose that smell permanently," Munger tells CNN.

For a sense of smell to return, "it might take days, it might take weeks, sometimes it even takes months to years on rare occasions. Sometimes it's gradual, sometimes it is all at once and we don't really know why that is," he adds.

"I'm at almost two weeks now and about 70% of my sense of smell has returned. One nostril is doing better than the other nostril," Bourne says.

Mark Driver, a 55-year-old winemaker from London, began to feel unwell with a cough, sore throat and mild temperature after coming into contact with a former colleague who has since tested positive in Dubai for Covid-19. On around day 8 of Driver's sickness, he lost his sense of smell. "This coincided with very severe headaches in the front of my head, just above the eyes," he says.

Mark Driver says his wine tasting is "appalling" and he still can't smell much at all.

"Smell is very important to my job, so I got a little worried that it might not come back." Twenty days since he first got sick, Driver says his wine tasting is "appalling" and he still can't smell much at all.

Sian Griffiths, 60, who normally runs a Bed and Breakfast in Argyll, Scotland, began feeling tired on March 28 and realized she had lost her sense of smell while cooking a curry the next day. "I realized I couldn't taste it, even when I inadvertently chewed a cardamom pod. This was rather disconcerting as I had no other symptoms such as a blocked nose," she says.

Like many others in the UK, she followed government guidelines and did not contact her local health service because she did not have a cough or fever. But she became concerned after a couple of days. "I tried sticking my nose right into a jar of coffee -- nothing. Whisky -- nothing. Frying bacon -- not a hint."

"Eating anything was most unpleasant, even repellent because I couldn't be sure that what I was eating was actually food," Griffiths adds.

The question about whether people are experiencing smell loss or taste loss comes down to the scientific or colloquial use of the word taste, Munger says. "When scientists talk about taste they are talking about what you can detect in your mouth that gives you a sensation -- sweetness, saltiness, bitterness, sourness, or umami (savoury). But taste plus smell is what your brain puts together to create flavor function," Munger explains.

Sian Griffiths noticed how losing her sense of smell meant she could no longer tell if food had gone off.

Griffiths noticed how losing her sense of smell meant she could no longer tell if food had gone off, saying "it's almost automatic to sniff a bottle of milk before pouring just in case it's on the turn." Speaking on what is day 12 without her full sense of smell, Griffiths says: "I now have slight hints of it returning. Almost as if some molecules are getting through. I caught a whiff of fresh paint where I had been painting woodwork a few days previously... I would say I have about 10% smell and taste now."

Amy Walker, 30, a finance and business manager from London, felt like she had come down with a bad cold and lost her sense of smell on March 18 -- more than three weeks ago.

"I was extremely lethargic, going from my bed to the toilet felt like I had run a marathon," she recalls. Walker had come into contact with someone who tested positive for coronavirus and called the NHS helpline but after spending a long time on hold, figured that because her symptoms weren't affecting her respiratory system she should just follow the advice given on the NHS website.

"The taste and smell both went together. I'm in recovery for an eating disorder that I've had for over half of my life and the loss of taste is an extremely triggering thing for me psychologically -- it immediately made me feel utterly miserable," Walker says.

"It brought back fears of food and an attitude of 'Well I can't taste it so what's the point of eating anything?' " she adds. "Being confined and so exhausted with those two senses taken away from you whilst there was panic and fear mongering everywhere was beyond draining."

Amy Walker felt like she had come down with a bad cold and lost her sense of smell on March 18.

Walker says her sense of taste and smell is now at around 50%, however, having a slight bit of taste and smell come back and then have no further progress has made her wonder if she's "now stuck like this".

One ENT doctor leading the charge to get loss of sense of smell recognized by the World Health Organization as a coronavirus symptom is Claire Hopkins, President of the British Rhinological Society.

Hopkins pushed for loss of sense of smell to be included in a coronavirus symptom-tracking mobile app developed by King's College London. Subsequently, on April, 1 King's reported its research found loss of sense of smell or taste is a stronger predictor of coronavirus infection than fever. Out of 400,000 people in the UK reporting one or more symptoms between March 24-29, 18% had lost their sense of smell or taste and 10.5% were suffering from fever.

Hopkins has been overwhelmed by the hundreds of people who have contacted her to share their experiences since issuing a letter on March 20 via ENT UK, an organization representing ear, nose and throat surgeons in the United Kingdom. The letter said patients with new-onset anosmia should self-isolate.

When one of her colleagues at Guys & St Thomas' Hospital in London circulated her letter, within five minutes she had 20 doctors telling her "this is exactly what I've got." One of them got a private Covid-19 test and tested positive that day, she says.

There is still a shortage of coronavirus testing taking place in the UK. For example, on April 9 the Department of Health reported little more than 10,000 people had been tested; the government's target by the end of the month is to test 100,000 per day, according to Health Secretary Matt Hancock.

This means patients and doctors alike are having to self-isolate based on symptoms, which obviously makes it even more important to know what the coronavirus symptoms are.

Since being inundated with enquiries after her letter was published, Hopkins has carried out an email survey on almost 2,500 patients experiencing sudden loss of sense of smell. At the time of filling in the survey, around 50% said they were already starting to see an improvement. At a one week follow-up, two-thirds reported they were already starting to see improvement, Hopkins says.

She advises that if you don't recover you should see a doctor when it's possible to have face-to-face consultations again.

Advice for sufferers

So what -- if anything -- can people do to aid the return of their sense of smell during the coronavirus pandemic?

For those feeling anxious and concerned, Munger says people should "recognize that it's legitimate."

From a safety perspective there is potential of failing to detect fires and consuming spoiled foods, but there is also "a real emotional component to smell, a connectedness that comes with it" that is linked to our social interactions that often revolve around food or drink.

"There's also that connectedness with the world: flowers, the smell of a partner's hair, all those types of things are very real and not having it can be emotionally isolating," he reasons.

One of the treatments that ENT doctors sometimes use for smell loss that might come from an inflammatory response is to use nasal steroids, Munger says. This involves spritzing steroids up into the nose to try and reduce inflammation.

Hopkins explains that normally in post-viral anosmia "we would consider the use of steroid tablets" however, that is not the case right now because the World Health Organization is warning against the use of oral steroids for people with Covid-19 infections, citing the potential risk of increasing the severity of respiratory complications.

"Until we know for sure that steroids won't cause harm, we are avoiding them, particularly in the first two weeks. Most people who deteriorate, deteriorate between day 8-12, in terms of respiratory complications. There is a potential that if you get past that 14 day window the risk of steroids might be less but nobody really knows," Hopkins adds.

For those types of treatments you would need to go and see a specialist, but there is another potential aid that Munger and Hopkins both suggest trying at home.

It's called "smell training" -- essentially sniffing things around the house that are safe to smell to help stimulate a response in the olfactory epithelium. That's a tissue in the very upper part of the nasal cavity, right against the skull, that contains the sensory system that responds to odors.

That's the part of the nose that appears to be damaged by the coronavirus, Hopkins said.

"We know that the coronavirus receptors -- the ACE2 receptors -- are found at very high levels in the lining of the nose and so it allows the coronavirus to attach into the nose and cause damage to the olfactory receptors that pick up the odors."

Smell training

According to FifthSense , a British charity for people affected by smell and taste disorders, for the training to be most effective you should practice smelling at least twice every day, ideally morning and evening. Relax and inhale naturally and don't sniff too hard or for too long. Ten seconds for each smell is enough.

Munger says it is unnecessary to use essential oils for smell training. If you don't have them, you can pick safe things out of your home: shampoo, mild spices, lemon juice.

"Just repeat it, over and over, and what it may be doing is helping the brain focus on that amount of smell function that is still intact and allowing you to maximize it," he explains.

"Think of it like learning to practice throwing a ball, or ice skating or a foreign language -- you are trying to use the apparatus that you have left to smell and your brain is making changes with repeated exposure to do it better."

He's cautious about its effectiveness, saying the "jury is still out" -- it's unclear if spontaneous recovery is because of the smell training or just occurs naturally -- but crucially, there is no harm in trying.

Although the science surrounding Covid-19 and taste and smell loss from case controlled studies does not yet exist, scientists and doctors around the world are working to gather data. The Global Consortium of Chemosensory Researchers (GCCR), a group of more than 300 international smell and taste researchers from 40+ countries, has launched a patient survey

For anyone still suffering with a lack of smell or taste more than two weeks after first getting sick during this pandemic, Hopkins has these reassuring words: "The good news is the vast majority of people are likely to recover."