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What is this and what causes it?

Everyone will experience anosmia at some point in their life when afflicted by a cold; we all know that feeling of being bunged up, unable to smell things properly or appreciate food.  Whilst the sense of smell usually returns once other symptoms clear, for some people the snotty nose and shivers depart but the lack of smell remains.

The exact mechanism behind post-viral anosmia isn’t yet understood, but it is clear that the various viruses that cause the common cold, including flu, somehow damage and interfere with the olfactory epithelium.  This is the layer of mucous membrane at the very top of the nasal cavity which contains the olfactory receptor cells.

This doesn’t always result in a complete loss of smell.  Those affected may be able to still detect certain odours, although the degree of this ability, and the odours themselves, varies from person to person.  What can compound the problem is the fact that PVOL patients are likely to be affected by parosmia, distortions of the sense of smell.  Again, the degree of parosmia varies from patient to patient.

Post-viral olfactory loss doesn’t always manifest itself suddenly, but can develop gradually over time. Many of us will get the common cold or a similar virus at least once or twice a year or more.  Some PVOL patients may experience a slight loss of smell following each cold, until after a particular bout they realise they cannot smell, without having noticed that it was deteriorating.

Post-viral olfactory loss tends to be more common in females between the ages of 40 and 70, although the reasons for this aren’t clear.

Prevalence

Prevalence

PVOL is responsible for around 12% of cases of olfactory loss

As we’ve said above, the mechanism by which viruses cause a loss of smell is not yet understood, which makes treatment difficult.  However, there are a number of positives.

Studies have shown that spontaneous recovery is more common in patients who have suffered postviral olfactory loss than with any other causation.  Any recovery is probably more likely to be partial than complete, however, and it isn’t possible to predict how long it will take for things to start to improve. That said, one study published in 2014 found that over 80% of participants experienced subjective improvement in olfactory ability one year after initial loss.¹

What can be a valuable aid in this case patients is smell training.  Several research studies have shown that smell training can be particularly beneficial to people who have suffered post-viral olfactory loss.²  It is thought that actively sniffing various odours such as the essential oils detailed on our smell training page can help the olfactory receptor cells regenerate and become active again.

PVOL and Parosmia

A major challenge for many people affected by post-viral olfactory loss is the fact that parosmia, a distorted sense of smell, is quite common with this causation.  These distorted smells are almost universally unpleasant, and can range in severity from being very mild to very severe.  This can potentially pose challenges to undertaking smell training as outlined above, but far worse than this is the effect it can have on people’s everyday lives.

How can this be treated and what are the challenges?

What can I do?

Smell Training – the sooner the better after the initial loss.  Whilst the mechanism by which this works is not yet understood, it is thought that smell training helps stimulate the regeneration of the olfactory receptor cells following their damage by the virus.

Relevant Research

Research studies referenced above:

1) Prognosis of postviral olfactory loss: follow-up study for longer than one year – Lee et al http://www.ncbi.nlm.nih.gov/pubmed/25198029

2) Olfactory Training is Helpful in Postinfectious Olfactory Loss: A Randomized, Controlled, Multicenter Study http://www.ncbi.nlm.nih.gov/pubmed/23929687

†) Gingko Biloba used alongisde prednisolone, a corticosteroid https://www.sciencedaily.com/releases/2009/10/091019172331.htm

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