The COVID-19 outbreak
highlighted an unusual
symptom for about a
third of patients — a
loss of the sense of smell. But the
disorder is neither new nor specific
to COVID-19.
Between 3 and 20 per cent
of people around the world
are believed to suffer from
the disorder, although it is not
known how many in Singapore
have the problem. The disorder,
which can also affect taste, can
be temporary or permanent,
depending on the cause. Causes
include viral infections, injuries
of the smell and taste nerves,
and medications.
“In general, viruses can
affect the nerves controlling
smell and taste, and cause these
disturbances,” said Dr Neville
Teo, Consultant, Department of
Otorhinolaryngology – Head and
Neck Surgery, Singapore General
Hospital (SGH).
Preliminary data from SGH
suggests that patients with
COVID-19 infection have a higher
chance of suffering from smell and
taste disturbances than patients
with other viral respiratory illnesses.
However, the exact reason for this
is still uncertain. Of the 870 SGH
patients with COVID-19 symptoms
seen between 26 March and 10 April
2020, 5 per cent had smell and taste
dysfunction at admission. Of the 154
patients confirmed with the virus
later, 23 per cent had the disorder.
Some COVID-19 patients have
reportedly lost their sense of smell
completely (known as anosmia)
or partially (hyposmia), while
others developed an altered sense
of smell. In the latter, the person
might smell something burning
when nothing around is on fire.
So far, the dysfunction among
COVID-19 patients appears
to be temporary for most, but
longer-term data are necessary to
confirm this, said Dr Teo.
In non-COVID-19 patients,
anosmia appears to be more
common among older people,
Dr Teo added. No specific data
exist for Singapore, but population
studies for the US show that about
half of those aged between 65 and
80 years have a reduced sense of
smell, with the number increasing
to three-quarters in those above
the age of 80.
Older people tend to be more
at risk because as people age,
changes in mucus secretions and
the lining of the nose occur.
The size and number of smell
receptors in the nose and brain
also shrink with age, contributing
to the greater possibility of the
disorder occurring.
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 cause the
disorder. In some cases, no cause
is found, Dr Teo said.
The disorder can be reversed
when the underlying cause, such
as an infection, is treated. A
complete recovery may take
weeks or months. “For the loss
of smell associated with an
underlying disease in the nose and
sinuses, treatment of the disease
can help patients regain their
sense of smell,” he added.
In cases of significant head
injury, or where the smell nerve
fibres were destroyed by tumours
or surgery, the loss of smell is
usually permanent. Medicines,
ranging from antibiotics and
antihypertensive medications to
chemotherapy drugs, can also
affect smell and taste. “If starting
a new medication coincides with
the onset of the smell disturbance,
the drug may be the cause.”
Anosmia, in any form
or severity, is not just an
inconvenience. “The main serious
complication associated with a
loss of smell is that one is not
able to detect noxious fumes in
the environment. This may be a
hazard at home if the gas stove is
left on unknowingly. For patients
with a complete loss of smell, this
is something to be cautious of,”
said Dr Teo.
With a loss of smell and
taste considered a COVID-19
symptom, Dr Teo advises anyone
experiencing the disorder to
seek treatment at polyclinics
or private clinics, based on the
latest guidelines available on
sgcovidcheck.gov.sg.