Allergy, Nose & Sinus

Loss Of Smell & Taste: Is It Covid-19 or Something Else?

blog-img Medically reviewed by Dr Gan Eng Cern, MBBS, MRCS (Edin), MMed (ORL), FAMS
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While fever, dry cough, and fatigue are symptoms that have characterized Covid-19, there’s another symptom that seems to affect the majority of those testing positive – the loss of smell or taste.

The temporary loss or distortion of one’s sense of smell and taste has, most recently, been identified as a symptom of Covid-19 and could perhaps even be the first.

However, other common ENT conditions such as sinusitis, common cold, and other upper respiratory tract infections can also rob you of these senses.

A study released by the University of San Diego found that you’re 10 times more likely to test positive for Covid-19 if you lose both your senses of smell and taste. Hence, losing your sense of smell and taste could signal early signs of Covid-19.

Since Covid-19 is a relatively new disease, little is known about the long-term outcome of patients with these symptoms. However, ongoing studies have provided some insight into what causes them, who experiences them and when we should be concerned.

Let’s dive deeper into the loss of smell and taste

The body’s chemical senses include smell, used to detect volatile odors, and taste, which recognizes food compounds such as sugars, salts, and amino acids.

Smell and taste disorders have been around for far longer than before Covid-19 surfaced.

Common conditions include:

  • Anosmia: loss of sense of smell
  • Ageusia: loss of sense of taste
  • Hyposmia: reduced ability to smell

Besides respiratory diseases such as Covid-19 and influenza, other conditions such as allergies, structural problems such as nasal polyps, and nerve issues could also result in one losing his or her sense of smell.

The loss of taste, on the other hand, is usually not impacted by viral upper respiratory infections but is rather closely intertwined with the loss of smell.

Retronasal olfaction is the perception of smell that comes from when odours leave the mouth and enter the nose through the connecting passage in the throat.

When we eat or drink, our brain combines this perception of smell with our perception of taste in the mouth to form flavour.

Hence, the loss of taste you experience could actually be more of a loss of flavour due to the reduced or absent ability to smell.

Scientists are still in the process of discovering if those with Covid-19 are actually losing their sense of taste temporarily or if it’s being impacted by their loss of smell.

How does coronavirus cause the loss of smell?

In most viral infections, the loss of smell is simply the result of a blocked nose – which prevents aroma molecules from reaching the olfactory receptors located in the nose. Hence, your sense of smell usually returns once your infection clears.

However, for Covid-19 patients, the pattern of smell loss seems to be different.

Most have reported a sudden loss of smell, followed by a full recovery within a week or two.

What’s more interesting is that many of them said that their noses were clear – eliminating blocked nose as a possible cause.

So, why else could you lose your sense of smell? Here’s the biology behind it:

The coronavirus, SARS-CoV-2, infects the body by attaching to ACE2 receptors on the surface of cells such as the sustentacular cells that line the upper respiratory tract.

Sustentacular cells are cells that support the olfactory neurons – which transmit the signal from the aroma molecule in your nose to the area in your brain where these signals get interpreted as “smell”.

A protein called TMPRSS2 on the surface of the sustentacular cells then helps the virus invade the cell. Once inside the cell, the virus replicates – triggering your immune system’s standard inflammatory response.

As a result, the immune system triggers swelling in the infected area. However, the olfactory neurons are left intact.

Hence, once the swelling subsides and the aroma molecules have a clear route to the undamaged receptors on these olfactory neurons, your sense of smell returns to normal.

However, for some, their loss of smell was prolonged and didn’t return for several weeks.

This could be because, during inflammation, the body releases chemicals to destroy the affected tissues.

When this inflammation is severe, other nearby cells start to get destroyed too – resulting in the damage of healthy olfactory neurons.

Hence, recovery is much slower since olfactory neurons need time to regenerate from the supply of stem cells within the lining of the nose.

What do we know about the Covid-19 cases where these symptoms occur?

Physicians around the world are reporting that up to 70% of patients who test positive for Covid-19 are experiencing a loss of smell and taste – despite not having fever, cough, or other typical symptoms of the disease.

According to this study, the loss of smell and taste also seems to be more prevalent in mild and moderate cases of Covid-19.

What if you don’t experience other Covid-19 symptoms?

While the loss of smell and taste can be caused by other conditions, it’s still important to remain alert and keep an eye out for other symptoms of Covid-19.

Since the loss of smell is one of the first (and sometimes only) symptoms in up to 25% of people diagnosed with Covid-19, it’s advisable to quarantine yourself and seek medical attention immediately if other symptoms appear over the next few days.

If you suspect you might be infected, go to the nearest Covid-19 testing facility accessible to you and get yourself tested.

Stay safe, stay healthy, and look out for your loved ones!