Khoo Bee Khim
CNA – The loss of one’s sense of smell has, most recently, been associated with COVID-19. But as you’ve probably experienced before, the common cold can also rob you of this ability.
And these aren’t the only reasons. According to Senior Consultant with Singapore General Hospital’s Department of Otorhinolaryngology – Head and Neck Surgery Dr Neville Teo, “viral infections, diseases affecting the nose and sinuses such as allergic rhinitis or sinusitis, head injury, and nerve disorders such as Parkinson’s disease” can also affect your ability to smell things.
Although, he added, “in some cases, no cause is found.”
While there’s no specific data for Singapore, Dr Teo said that anosmia (the complete loss of smell) and hyposmia (reduced sense of smell) is thought to afflict three per cent to 20 per cent of our population.
WHAT’S THE CONNECTION WITH COVID-19?
Since the loss of smell is currently linked with the coronavirus, let’s start with that. According to Dr Teo, in addition to anosmia, COVID-19 could also bring about hyposmia or alter your sense of smell.
“An altered sense of smell is smelling a scent that is not actually present, such as a burning smell when there is nothing burning around you,” he said.
“Early data suggests that the majority of smell disturbances from the COVID-19 infection is temporary, although more long-term data is needed to determine this, especially in our local context,” said Dr Teo.
Medical Lead Dr Nate Favini at Forward, a US preventive primary care practice, noted that if losing your sense of smell is your only symptom, it’s unlikely to be COVID-19.
Besides, the flu can also cause loss of smell in 30 per cent of patients, he told Healthline. “It’s a common symptom for respiratory viruses and isn’t specific to COVID-19.”
Meanwhile, a study released by the University of San Diego found that you’re 10 times more likely to have COVID-19 if you lose both your senses of smell and taste.
In fact, Dr Carol Yan, one of the researchers and an otolaryngologist at UC San Diego Health, said that “this study supports the need to be aware of smell and taste loss as early signs of COVID-19”.
In Singapore, the authorities have included the loss of taste or smell as one of the symptoms of COVID-19. Dr Teo noted that it’s not surprising that anosmia can also affect the sense of taste. “The flavours of foods are contributed by the sense of smell, so alteration in smell can also lead to an altered taste sensation.”
WHY DOES AGE AFFECT YOUR SENSE OF SMELL?
But anosmia is not a novel issue and neither is it uniquely linked to COVID-19 or any particular sickness.
In fact, ageing has something to do with it as well. The older you are, the more likely you are to lose your sense of smell. It is also the likely reason why older individuals aren’t able to taste food well.
“Population studies from the United States show that about half of those aged between 65 and 80 years old have a reduced sense of smell,” said Dr Teo, adding that the cases increase to three-quarters in those above the age of 80. However, there is no fixed age at which the loss starts to happen.
There are a few reasons for this. “Changes in the mucus secretions in the nose, lining of the nose and decreased nasal clearance of mucus occur with age,” explained Dr Teo. “Reduction in the size and number of smell receptors in the nose and the brain with age also contribute to the increasing occurrence.”
Furthermore, older people are more likely to be put on anti-hypertensive medications to control their blood pressure. And these medicines can alter your sense of smell and taste, said Dr Teo.
Similarly, antibiotics and chemotherapy drugs may have the same effect.
IF IT HAPPENS, CAN YOU SMELL THINGS AGAIN?
It depends on the cause of the loss. If you’ve lost your sense of smell to an infection (such as allergic rhinitis or sinusitis), trauma or other underlying causes, your ability to smell can return if the underlying cause is treated, said Dr Teo.
But things are different in instances where the smell nerve fibres are damaged or injured, which can happen after a head trauma, tumour, surgery or even a viral infection, he said. “The loss of smell is usually permanent and irreversible.”
Sometimes, steroids may be used to help restore the sense of smell when there is no specific cause behind the loss of smell and taste, said Dr Teo. But the outcome may not be as effective.
“Smell training is another option, which can potentially improve smell identification,” he said.
According to Professor Thomas Hummel, an ear, nose and throat expert at the University of Dresden in Germany, that involves smelling odours on a regular basis.
In an interview with the BBC, Professor Hummel said that four odours are used: Rose, eucalyptus, cloves and lemon.
These odours are picked as they seem to “affect growth of olfactory receptors in the nose”, he said, adding that each odour is sniffed for 20 seconds, twice a day.
Prof Hummel found that 45 per cent of people with anosmia improved with training.
Without training, only 22 per cent were able to smell again.