Smell loss is a common symptom of respiratory illnesses, including COVID-19.
By Annie Hayes
It’s common for upper respiratory infections such as the common cold or flu – or allergies like hay fever – to temporarily impair your sense of smell. Known medically as anosmia, the symptom also occurs in approximately half of COVID-19 cases. While around two thirds recover within eight weeks, many are still affected by loss of smell.
Smell plays a huge role in memory, mood and emotion. Your sense of smell and sense of taste work together to create the perception of flavour, so losing the ability to detect aromas can greatly affect your relationship with food. At the more extreme end of the spectrum, smell loss can even endanger your life – if you fail to detect a gas leak, for example.
We spoke to smell loss expert Professor Carl Philpott from the University of East Anglia’s Norwich Medical School about the common causes behind smell loss, the ways in which anosmia affects quality of life, and how smell training can help to reverse the condition:
What causes smell loss?
Smell loss is most commonly caused by chronic sinusitis, rhinitis, and similar conditions that swell the mucous membrane lining the nose, called the olfactory epithelium. These illnesses can lead to a temporary loss of smell, which tends to return on its own.
If the pathway between the brain and the nose malfunctions due to brain or nerve damage, this can result in a permanent loss of smell. There are many conditions that can cause this damage, including Alzheimer’s disease, multiple sclerosis, alcoholism and even old age.
Smell loss is most commonly caused by conditions that swell the mucous membrane lining the nose.
Not everyone experiences a complete loss of smell. Some find they can still detect certain odours, known as hyposmia. Among others, their sense of smell is distorted, known as parosmia – a bowl of porridge, for instance, may smell like rotting fish. People may also experience phantosmia, which means they smell things that are not there.
Loss of smell and COVID-19
Smell loss is also a prominent symptom of COVID-19. It tends to last longer compared to other upper respiratory infections, and can take up to four weeks to improve. Often, people with COVID-19 experience loss of taste as a consequence of their loss of smell. The virus isn’t thought to affect your smell receptors directly, but the area around them.
Research shows the virus gets into deeper structures in the brain and has a more central effect on smell performance.
‘The working theory is that the coronavirus gets into the cells that sit around the smell receptors, called the supporting cells,’ says Professor Philpott. ‘It causes that layer to swell, squeezing the smell receptors, which has an indirect effect on their function. It’s thought that’s why there’s often a sudden onset.’
If so, this may also explain why smell loss is usually a relatively short-lived phenomenon. But among some people, the symptom has been shown to linger long-term. ‘There is research that shows the virus is getting into deeper structures in the brain and having a more central effect on smell performance,’ says Professor Philpott.
The effects of smell loss
Losing your sense of smell can have a profound effect on your quality of life. As well as obvious dangers – being unable to smell expired food, or detect gas or smoke – there are emotional and practical effects. In a study co-authored by Professor Philpott at the University of East Anglia, the team found that almost every area of life is disrupted by smell loss, from concerns about personal hygiene to a loss of sexual intimacy with partners.
‘About two thirds of patients report depression or anxiety as a consequence of smell loss,’ says Professor Philpott. Among people who suffer long-term, ‘around one third will report losing weight because they lose all interest in food,’ he says. ‘Another third report gaining weight, because they go out of their way to stimulate their senses by eating takeaways and comfort eating.’
Many report feelings of isolation, ‘because they feel a disconnect from the social ethos connected to eating, but also to memories,’ Professor Philpott continues. Smell loss can make it difficult to bond with loved ones, ‘particularly partners,’ he says. ‘Some people experience an inability to maintain relationships or to form new ones because of the subconscious connection through smell.’
In the study, parents of young children couldn’t tell when their nappies needed changing. One mother found bonding with her baby difficult. Smell loss can affect your career, too. ‘People who use their sense of smell on a professional basis are significantly impacted,’ says Professor Philpott. Doctors, for example, may miss an infected wound. Social workers may find it trickier to identify whether their client is drinking too much alcohol.
How to test your sense of smell
If you suspect you may be losing your sense of smell, use common household items to put your nose to the test:
- Find a handful of items that have a strong, easily identifiable smell, such as coffee, garlic, mint or oranges.
- Hold each item close to – but not touching – your nose and inhale.
- Don’t use anything that could be an irritant, such as cleaning products.
- If you have trouble picking up the scents of your selected items, you may be experiencing a loss of smell or taste.
⚠️ If loss of smell symptoms develop suddenly, this may indicate the early onset of COVID-19. The current government advice outlines that you should arrange to have a test for COVID-19 and stay at home and self-isolate for 10 days from when your symptoms start.
If you do not test positive for COVID-19 or your lack of smell persists long after you have recovered from the virus speak to your GP, as you may need to see an ENT Specialist to investigate further.
How to recover your sense of smell
Repeated short-term exposure to smells, known as smell training, has been shown to benefit people with smell loss – particularly those who have lost their sense of smell due to a virus, such as the common cold. It’s suggested that you use scents from four categories – flowery, fruity, spicy and resinous – however, this is only a recommendation.
‘Smell training is a simple process that you ideally do for a couple of minutes, twice a day,’ says Professor Philpott. ‘Traditional studies use eucalyptus, rose, lemon, and clove, but they’re by no means prescriptive. I’d suggest using a smell that you are familiar with before you experienced smell loss that is readily available to you.’
Smell training has been shown to benefit people with smell loss who lost their sense of smell to a virus.
While you can hold the raw materials in your hands if you choose, decanting the source of your chosen scent can prove even more effective. ‘Liquids work quite well, because you can put them in a jar,’ Professor Philpott explains. ‘By doing so, you create a vapour space above the liquid, which creates molecules that you can detect during the training process.’
Once you’ve prepared your scents, smell loss charity Fifth Sense recommends analysing each one individually as follows:
- Relax and slowly and gently, inhale naturally – sniffing too quickly and deeply is likely to result in you not being able to detect anything.
- Repeat 2 or 3 more times, then rest for five minutes.
- Move on to the next smell and repeat as above.
- Record your experience – note down any changes and what you notice.
The minimum period for smell training is three months, ‘but it really does depend on individual response,’ says Professor Philpott. ‘More recent studies have looked at the duration of training.’ One study compared a group that trained for 16 weeks with a group who did so for 56 weeks. ‘Those who did it for a whole year got a much better result that those doing it for a shorter period,’ he says.
There are also benefits to changing the smells every four weeks, known as modified olfactory training. ‘Changing the odours regularly is the other key principal,’ says Professor Philpott. ‘That appears to have an increased benefit on recovery of smell.’ In this instance, essential oils may be useful. Just be sure to keep the lid screwed on tight in-between training sessions, and store them in the fridge or another appropriate cool, dry place.
How does smell training work?
Smell training helps recovery based on neuroplasticity, says Professor Philpott, which refers to ‘the brain’s ability to reorganise itself to compensate for a change or injury’. It’s a similar training device that perfumers and sommeliers adopt when learning to pick out scents. ‘You can get a turnover of smell receptors as consequences of the stimulation,’ he says.
Other studies have shown ‘changes in the olfactory bulb, which is the relay station where the smell nerves that come from the nose connect to the nerves that go into the brain,’ says Professor Philpott. ‘Those structures are known to be plastic… and can increase in size when you get things moving again.’ The same studies have shown changes that benefit the entire nose-to-brain pathway, improving its functionality.
Smell training doesn’t have to end when your daily session is complete. In fact, you should use every possible opportunity to stimulate your olfactory system. Whether you’re cooking a meal, indulging in a spot of gardening, or hanging freshly-washed clothes, focus on paying attention to the source of the scent as you breathe in. This will help you recall memories associated with the scent and support your regular day-to-day training.