How to restore loss of smell, taste after COVID-19

As the COVID-19 pandemic spread around the world anosmia and dysgeusia were quickly recognised as two of the key presenting symptoms. Temporary loss of smell, or anosmia, is the main neurological symptom and one of the earliest and most commonly reported indicators of COVID-19. For today’s article our source person is Dr. Sujeewa Weerasinghe who is the National Organizer of the Chartered Society of Physiotherapist and the vice President of the World Disability and Rehabilitation Professionals Association. 

Patients with viral upper respiratory infections to experience a temporary — or sometimes permanent — loss of taste or smell. These symptoms appear to be particularly prevalent in COVID-19. Studies suggest it better predicts the disease than other well-known symptoms such as fever and cough, but the underlying mechanisms for loss of smell in patients with COVID-19 have been unclear. Up to 80% of people who test positive for COVID-19 have subjective complaints of smell or taste loss. That percentage rises when these patients are tested using objective methods that measure smell function. Most patients first notice problems with their sense of smell, but because the smell is necessary to taste the flavor, the symptoms are often connected.

Now, an international team of researchers led by neuroscientists at Harvard Medical School has identified the olfactory cell types in the upper nasal cavity most vulnerable to infection by SARS-CoV-2, the virus that causes COVID-19. Several studies suggest that infection of nonneuronal cell types may be responsible for anosmia in COVID-19 patients and help inform efforts to better understand the progression of the disease. This implies that in most cases, SARS-CoV-2 infection is unlikely to permanently damage olfactory neural circuits and lead to persistent anosmia, Datta added, a condition that is associated with a variety of mental and social health issues, particularly depression and anxiety.

How can a virus cause smell and taste loss?
People with upper respiratory infections often have congestion, drainage, and other nasal symptoms that can block odor’s ability to reach the smell nerve, which sits at the top of the nasal cavity. But, we believe the primary cause, particularly for people with extended or permanent loss of smell function, is that the virus causes an inflammatory reaction inside the nose that can lead to a loss of the olfactory, or smell, neurons.

Surprisingly, sensory neurons that detect and transmit the sense of smell to the brain are not among the vulnerable cell types. The probability of return of smell is related to the severity of smell loss at presentation, but it appears that the loss of sense of smell and taste seems to persist in approximately 10% of the affected patients after 6 months. As a result of COVID-19, it is estimated that within the next 12 months.

The probability of return of smell is related to the severity of smell loss at presentation, but it appears that the loss of sense of smell and taste seems to persist in approximately 10% of the affected patients after 6 months

While many people report a loss of taste as a primary symptom, or some people experience the loss of smell as their only COVID-19 symptom and no one knew how long people would lose their sense of smell or if it would ever return. It’s a loss of smell that’s often a worse culprit since most of what we perceive as taste is a combination of smell and taste. It’s estimated that 50% of COVID-19 patients experience changes to their sense of taste and smell. 

Momentary loss of smell in this setting is typically from congestion or inflammation in the nose. Things get enlarged and the scents simply are not getting to the smell receptors that live high in the nose. With longer-term cases, that stretch on for quite a long time or even forever the issue might be harmful to the smell receptors or olfactory nerves themselves. That is the thing that we think when we take a gander at a CT check or an MRI and don’t perceive any actual indications of the clog or apparent actual change

Most will recover within two to three weeks, but many of them are still working towards recovery many months later, but new research shows it can continue up to five months after the virus first strikes. When this damage occurs as part of COVID, it tends to be a more extreme issue than when people lose those senses due to other respiratory issues. This is quite common in many infectious diseases, but in COVID, the effect was much more important. In other viruses, smell and taste usually return after the sinuses are clear. But in COVID-19, the virus might penetrate the small area of the brain called the olfactory bulb, which is important for the recognition of smell. The virus probably kills some of the cells in the olfactory bulb, and that’s why you have a long-lasting effect

Smell training could help recovery 

Smell therapy or smell training, also referred to as olfactory training, is not a new procedure formulated recently to resolve anosmia and parosmia in patients with COVID-19. Olfactory training for COVID-related smell loss but what if your patients could train themselves to smell again? That’s the thinking behind olfactory training and it would be worth trying even for COVID-related smell loss. The idea is that it’s an extremely safe, self-driven treatment option with no side effects that’s been helpful, including in post-viral cases of smell loss. Smell training has no known side effects and is low cost. Moreover, it is the only available treatment… supported by a robust evidence base.

smell therapy that works by rewiring the brain’s smell-linked nerve channels i.e., the olfactory nerves, and repairing damaged olfactory receptors, olfactory bulbs – which happen in COVID-19, which are the organelles that recognize and process smell. This in turn renews memory and emotions associated with distinct odors, thereby helping restore normal olfactory perceptions.

This basic technique of smell training is where Patients are instructed to gently smell different essential oils or herbs with familiar scents for 20 seconds while focusing on their memories and experiences with that scent. Sniffing four items with a distinct odor - rose, cloves,  eucalyptus, lemon, for 20 seconds, twice a day, for 3 months. People who actively performed smell therapy for the entire period of 12 weeks were able to dispel olfactory dysfunction and enhance their sense of smell. The basis for choosing these specific four items for smell therapy is that just like there exist three primary colors of red, blue, and yellow, there are four primary smells – floral i.e. rose, fruity – lemon, aromatic – with cloves and resinous – eucalyptus.