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by Adam Brown   BScPT
Long COVID Rehabilitation Physiotherapist
updated Feb 10, 2022


Anosmia refers to a complete loss of the sense of smell. Dysosmia is a partial loss of the sense of smell. It occurs for a variety of reasons including head injury, sinus infection or other viral infections. Since late 2020 the incidence of anosmia has increased dramatically because it is a frequent complication of COVID-19 infection. There are thousands of documented reports of patients experiencing partial or full loss of smell and taste following a COVID-19 infection.


Are Smell Disorders A Big Problem?

In a word, Yes. A clinical review by Boesveldt et al. came to the conclusion that anosmia causes a profound negative impact on a patients quality of life. Our sense of smell provides us with a great deal of important information to help us navigate our lives. The smell of smoke or gas may alert us to danger in our immediate area.

Patients who suffer from anosmia also tend to have a very reduced sense of taste because our tongue and our nose work together to produce what we know as taste. Determining if a food item has gone bad is a much more difficult task if you have an impaired sense of taste and smell.

Not only is there potential danger from the loss of smell and taste, there is a profound reduction in the pleasure that can be experienced from delicious food that people would otherwise enjoy.


How does COVID-19 Cause Anosmia?

Each case of loss of smell is a little bit different and may be triggered by different situations. For instance, in the case of head trauma it has been suggested that the olfactory neurons (smell receptors) can become damaged from sheer force where they pass through the skull into the nasal cavity. 

There is some exciting research that was published in the journal “Cell” in February 2022 that suggests a possible cause of anosmia in patients after COVID-19 infection. The research was conducted on hamsters (Hamsters have remarkably the same symptoms and response to treatments of COVID-19 as humans do). 

The researchers found that COVID-19 infection resulted in high levels of inflammation that damaged cells in the olfactory bulb (smell receptor area) called SUS cells. These cells help to organize the functioning of olfactory neurons in this area. This high degree of inflammation causes the olfactory cells to use up most of their energy dealing with the inflammation from the surrounding cells, significantly reducing their ability to process smells. The good news is that in most cases the olfactory neurons themselves were not damaged, but were temporarily weakened by dealing with the consequences of the nearby inflammation. As this inflammation resolved most of the subjects’ sense of smell returned. This may be a clue as to why steroid medications seem to help many people suffering from post-viral olfactory dysfunction.

It has been shown that many of the complications of COVID-19 are linked to increased and widespread inflammation in the body. Research questions must now focus on the best ways to eliminate this inflammation safely and effectively.


Can The Sense of Smell Be Tested?

There are clinical tests designed to test a patients sense of smell. One popular test uses a product called “Sniffin Stix” (not joking) and it involves a protocol that allows a clinician to objectively test a persons olfactory impairment. These tests are used in research applications to determine efficacy, but are more difficult to find in the regular medical community.


Can You Get Your Sense of Smell Back After COVID-19?

Approximately 60% of patients who have a reduction in their sense of smell experience a spontaneous resolution of their symptoms.  Your chances of spontaneously regaining your sense of smell improves if you are young, female or a non-smoker. Which is to say that if you had good olfactory function prior to infection, you are more likely to have your sense of smell return after infection.

However, that leaves 40% of people that do not experience immediate resolution. Within this group some will recover over a prolonged timeline and others may not recover at all.


What Are The Treatment Options For Anosmia?

If you are experiencing anosmia following a COVID-19 infection you should start by talking to your doctor. Through a physical examination they can begin the process of ruling out any other causes that may need to be addressed. A number of treatments for anosmia are under investigation but only two have consistently shown to help.


Jafari and Holbrook conducted a meta-analysis of the treatment literature on treatments for anosmia and concluded that short term topical and systemic corticosteroid use is sufficiently supported by the literature to be used as a treatment for anosmia related to COVID-19 and other infections. Most patients experienced minimal if any side effects, but of course corticosteroid use should be prescribed by your doctor and supervised appropriately.

Olfactory Training

The other treatment that has consistently shown to help people recover from anosmia is olfactory training. This is a protocol where people use a series of scents and intentionally smell them several times a day to begin to train their olfactory system to process smells again. There are many protocols used throughout the literature. Most use 4 or more strong scents repeated twice daily.

It is worth noting that the research in this area tends to get the best results when corticosteroid use is combined with olfactory training.


Does Olfactory Training Really Work?

It sure does! Damm et al conducted a randomized, controlled, multi-centre study that found that olfactory training improved post-infectious olfactory dysfunction. The study also noted that it tends to work better when higher concentrations of the scent are used and when patients begin training within 12 months of the onset of the disorder.

A recent study with over 100 patients showed that 71% of participants with post-infectious olfactory dysfunction improved with olfactory training over one year, while only 37% of patients without olfactory training spontaneously recovered over the same time period.

Not only does olfactory training have promising results, the very nature of it means it is safe and has no undesirable side effects.


How Do You Do Olfactory Training?

To begin olfactory training at home will require you to find a few concentrations to smell and to commit some time to the process every day. Here are some tips on getting started with olfactory training.

  • If you are a smoker, now is the time to quit. Your chances of success increase a great deal.
  • Common scents used are  phenylethyl alcohol (rose scent), eucalyptol (eucalyptus scent), citronella (lemon scent), and eugenol (clove scent­).
  • Feel free to find other concentrated scents to add to your regime to improve your chances of success.
  • Put each scent into a small jar that can be closed up between sessions.
  • Take time twice each day to sniff each scent for a full 30 seconds each.
  • Sniff for the full 30 seconds with each scent with no breaks.
  • Settle in and be patient. Many patients see results over the course of 25 weeks and some need to persist for a year.


Where Can I Get Help For My Reduced Sense Of Smell?

As mentioned earlier, start with your primary care doctor. if you have had, or are suspected of having COVID-19 and your loss of smell came on as a result, get in touch with us at Cornerstone Physiotherapy and one of our COVID-19 rehabilitation trained therapists can help advise you on how to get started with olfactory training.

About the author

Adam Brown

Co-founder, Physiotherapist Learn More about Adam Brown

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