Anosmia is the medical term for a complete loss of smell. A reduced sense of smell is called hyposmia. Although smell loss became widely recognised during the COVID-19 pandemic, there are many other possible causes, including nasal polyps, chronic sinusitis, viral infections, head injury and problems affecting the olfactory nerve.
Why have I lost my sense of smell?
There are two broad ways in which smell can be lost.
The first is conductive smell loss. If the nose is blocked by inflammation, nasal polyps or sinus disease, odour molecules may not reach the specialised smell receptors high inside the nose. Treating the underlying nasal problem can sometimes restore the sense of smell.
The second is nerve-related or sensorineural smell loss. In this situation, you may be able to breathe normally through your nose, but the olfactory nerve cells or the pathways connecting them to the brain are not working normally. This can occur following viral infections, including COVID-19, or after a head injury.
Sometimes both mechanisms are involved.
Anosmia and COVID-19
COVID-19 brought anosmia into the public consciousness. During the first wave of the pandemic, ENT doctors noticed that sudden loss of smell could be an early symptom of COVID-19, sometimes occurring without a blocked or runny nose.
There was an unusual opportunity to study this using Google searches. Researchers found that searches for terms such as “loss of smell” and “anosmia” rose alongside COVID-19 cases in several countries. One early study, involving researchers from Guy’s and St Thomas’ in London, found strong correlations between smell-loss searches and COVID-19 cases and deaths.
It was an intriguing example of using population search behaviour as a potential epidemiological tool. However, later research showed that media coverage itself strongly influenced searches, meaning that Google searches could not reliably be used on their own to track COVID-19 outbreaks.
Why is smell so interesting?
Our sense of smell is remarkably sophisticated. In 2004, Richard Axel and Linda Buck won the Nobel Prize in Physiology or Medicine for their discoveries concerning smell receptors and the organisation of the olfactory system.
Smell is also closely connected to memory and emotion. William Wordsworth understood the power of sensory experience to evoke memories. A particular perfume, meal or the smell of a place can instantly transport us back to another time.
For someone with anosmia, this whole dimension of everyday life can disappear.
If you want to explore the subject further, On the Scent by Paola Totaro and Robert Wainwright is an engaging book about the science and personal experience of losing smell.
Can you retrain your sense of smell?
One of the most useful treatments for persistent post-viral smell loss is olfactory training, commonly known as smell training.
This involves deliberately smelling several distinctive odours – traditionally rose, lemon, clove and eucalyptus – twice a day for several months, concentrating carefully on each smell.
It is rather like physiotherapy for the smell system. Studies suggest that olfactory training can improve smell function in people with post-viral smell loss, although recovery varies considerably between individuals.
What about omega-3 supplements?
There has been interest in whether omega-3 fatty acids might help recovery of the olfactory system, partly because of their potential anti-inflammatory and neuroprotective effects.
A small pilot study found that omega-3 supplementation alongside smell training produced a greater improvement in odour threshold than smell training alone. However, a larger placebo-controlled study of persistent COVID-related smell loss did not demonstrate a significant additional benefit from omega-3 supplementation.
For this reason, I would regard omega-3 as an interesting but unproven adjunct, rather than a treatment that can currently be recommended as a proven cure for anosmia.
Where can I find more information?
AbScent has been an excellent source of information and support for people affected by smell disorders, with particularly useful resources on anosmia, parosmia and smell training.
If your sense of smell has suddenly disappeared, has become distorted, or has failed to recover after an infection or head injury, an ENT assessment can help establish whether the problem is caused by nasal blockage, inflammation or dysfunction of the olfactory system.
Smell may be easy to overlook – but when it disappears, we quickly discover just how important it is.