The loss of smell that can accompany coronavirus is unique and different from that experienced by someone with a bad cold or flu, say European researchers who have studied the experiences of
patients. When Covid-19 patients have smell loss it tends to be sudden and severe. And they usually don't have a blocked, stuffy or runny nose - most people with coronavirus can still breathe freely. Another thing that sets them apart is their "true" loss of taste. It's not that their taste is somewhat impaired
because their sense of smell is out of action, say the researchers in the journal Rhinology. Coronavirus patients with loss of taste really cannot tell the difference between bitter or sweet. Experts suspect this is because the pandemic virus affects the nerve cells directly involved with smell and taste sensation. The main symptoms
of coronavirus are:
Anyone with these symptoms should self-isolate and arrange to have a swab test to check if they have the virus. Members of their household should isolate too to prevent possible spread.
Media caption,
Covid symptoms: What are they and how long should I self-isolate for?
Smell research
Lead investigator Prof Carl Philpott, from the University of East Anglia, carried out smell and taste tests on 30 volunteers: 10 with Covid-19, 10 with bad colds and 10 healthy people with no cold or flu symptoms.
Smell loss was much more profound in the Covid-19 patients. They were less able to identify smells, and they were not able to discern bitter or sweet tastes at all.
Prof Philpott, who works with the charity Fifth Sense, which was set up to help with people with smell and taste disorders, said: "There really do appear to be distinguishing features that set the coronavirus apart from other respiratory viruses.
"This is very exciting because it means that smell and taste tests could be used to discriminate between Covid-19 patients and people with a regular cold or flu."
He said people could do their own smell and taste tests at home using products like coffee, garlic, oranges or lemons and sugar.
He stressed that diagnostic throat and nose swab tests were still essential if someone thought they might have coronavirus.
The senses of smell and taste return within a few weeks in most people who recover from coronavirus, he added.
Prof Andrew Lane is an expert in nose and sinus problems at Johns Hopkins University in the US.
He and his team have been studying tissue samples from the back of the nose to understand how coronavirus might cause loss of smell and have published the findings in the European Respiratory Journal.
They identified extremely high levels of an enzyme which were present only in the area of the nose responsible for smelling.
This enzyme, called ACE-2 (angiotensin converting enzyme II), is thought to be the "entry point" that allows coronavirus to get into the cells of the body and cause an infection.
The nose is one of the places where Sars-CoV-2, the virus that causes Covid-19, enters the body.
Prof Lane said: "We are now doing more experiments in the lab to see whether the virus is indeed using these cells to access and infect the body.
"If that's the case, we may be able to tackle the infection with antiviral therapies delivered directly through the nose."
What is anosmia?
Anosmia is the complete loss of your sense of smell. It can be temporary or permanent. (If you just have a reduced sense of smell, we call this hyposmia.)
A lack of smell happens either when odorants (particles of odour) cannot reach the olfactory lining inside the nose, or when there is damage to the olfactory nerves.
The longer anosmia goes on for, the greater the need for your nose and sinuses to be examined by an expert and the more likely you are to need a scan to investigate further.
Does anosmia also affect your sense of taste? Are there any other symptoms?
75-80% of what we perceive as taste actually comes from smell, so it’s no surprise than anosmia can affect our sense of taste
Orthonasal olfaction is when you smell something through sniffing. During this process, air carries odours high up inside the nose.
Retronasal olfaction is where food odours from the oral cavity (i.e. your mouth) pass into the nose while you eat. 75-80% of our flavour perception actually comes from this process, so it is no surprise that anosmia can affect our sense of taste as well as smell.
Any problem that interferes with smell can also interfere with taste. This can reduce the pleasure we have when eating and drinking, which can certainly affect quality of life.
More serious results of both permanent and temporary loss of smell include not being able to smell gas leaks or smoke, or less dangerous but still important smells like a soiled nappy.
If you lose your ability to smell these things, it’s important to take precautions (such as alarms in your home), and potentially ask for help with childcare while you recover.
What are the most common causes of anosmia?
Common causes of anosmia include viruses; allergies such as tree pollens, grass pollens, animals and dust; a deviated septum; nasal polyps; or an injury to your head – even just a small bump.
Other, less common causes include sinusitis, damage to the central nervous system, and tumours.
Usually, you can diagnose anosmia easily using an endoscope and maybe also a scan to examine your nose.
Around 70% of people with COVID-19 report losing their sense of smell
Can COVID-19 cause anosmia?
Yes, COVID-19 can absolutely cause a loss of smell. In fact, it is the most common presentation of the coronavirus infection, more common than either a new-onset cough or a high temperature.
Around 70% of people with COVID-19 report losing their sense of smell, or both taste and smell. This is why Public Health England has recognised anosmia as an important symptom of COVID-19 infection.
If you suddenly lose your sense of smell, it is crucial that you follow government advice for self-isolation, even if you don’t have any of t the other COVID-19 symptoms.
However, it is really important that you (or your doctor) don’t automatically assume that a loss of smell and taste is due to COVID. There are other possible causes that should be ruled out too.
The longer you are without your send of smell or taste, the more important it is for you to be assessed by an ENT (ear, nose and throat) specialist. This is especially true if you don’t think you have had COVID-19.
How long do people normally lose their smell for?
Post-viral anosmia is very common, both from COVID-19 and other viruses. Around 40% of people with an upper respiratory viral infection will experience loss of smell.
Thankfully, around 90% of people will start to recover after 2-3 weeks, for COVID as well as other infections. COVID-related anosmia behaves in the same way as anosmia resulting from other upper respiratory viruses, of which there are around 200!
The majority of the remaining 10% of people will take a while longer to recover, usually up to 12 weeks after the onset of the infection. Again, this is the same for coronavirus-related illnesses.
Although it is rare, there are some cases where people will lose their sense of smell permanently after a viral infection.
Can anosmia be cured?
Anosmia caused by a virus can’t technically be cured; in most people it tends to just recover over a period of time. For most people, smell returns after 3-12 weeks.
What treatments are available for anosmia?
The treatment you are recommended will depend on the cause.
For non-COVID anosmia, your ENT specialist may prescribe you a spray, an antihistamine or a steroid tablet to decongest the olfactory area in your nose, hopefully improving your sense of smell. Some people might need surgery on their septum, polyps or sinuses.
For people with post-viral anosmia, the only treatment currently proven to help is olfactory training (also known as smell training). This method can potentially help to amplify your recovery.
You can purchase a smell training kit from the charities AbScent and Fifth Sense, which also give detailed explanations of how the process works and offer various resources to support you through anosmia.
You may have read about other proposed treatments for anosmia, such as omega 3, vitamin A drops or alpha-lipoic acid. The evidence that these help your smell recover is not very strong, but they are unlikely to do you any harm.
What should I do if I lose my sense of smell?
The most important thing to do is follow current government advice. If you lose your sense of smell, use the government website to book a test, and be sure to quarantine/self-isolate before and after the test.
Whether or not your test for COVID-19 was positive, you should keep in mind that you may need to see an ENT specialist if your anosmia lasts for a long time. Current advice is to see a specialist after six weeks if you have not had COVID, and 12 weeks if you tested positive for COVID.
It’s important to see a specialist in case there is some other reason behind your anosmia, because viral infections are not the only possible cause.