Introduction
Loss of smell is being reported as common and prominent symptom of COVID-19.1
A recent study reported that one in five people who experienced smell loss as a result of COVID-19 reported that their sense of smell had not returned to normal eight weeks after falling ill. The report states that 90 percent of people fully recovered their sense of smell after six months.2
Another study evaluating a small group of patients with COVID-19 related anosmia beyond 7 days. The results found that 28.2% reported satisfactory recovery of olfaction within 4 months, while the remaining 71.7% did so by 12 months.3
A study from Virginia Commonwealth University reported the sense of smell or taste returns within six months for 4 out of every 5 COVID-19 patients who have lost these senses, and those under 40 are more likely to recover these senses compared to older patients.4
This paper went on to report that using smell training using essential oils may help.4
A report from the University of East Anglia also suggested that smell training could be beneficial. This involves sniffing at least four different odours twice a day every day for several months. Smell training is reported as an inexpensive, simple and side-effect free treatment option for various causes of smell loss, including COVID-19.2
The aim of smell training is to help recovery based on neuroplasticity; allowing the brain to reorganise itself to compensate for a change or injury.2
These studies all indicate that patients affected by COVID-19 can experience decreased sense of smell or total loss of smell for 6 months up to 12 months after the infection.
Pathophysiology of SARS-CoV-2 infection on olfaction
Researchers have confirmed the olfactory cells in the upper nasal cavity are most vulnerable to infection by SARS-CoV-2. However, the sensory neurons that sense smell are not the vulnerable cell types.5
SARS-CoV-2 infects host cells by the virus’s spike protein binding to the viral receptors angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2). Both of these receptors are highly expressed in the gastrointestinal tract, in the nasal and bronchial epithelium as well as in the type II alveolar epithelial cells.5
Olfactory neurons do not express the gene that encodes the ACE2 receptor protein, which SARS-CoV-2 virus uses to enter human cells. Instead, ACE2 is expressed in the cells that provide support to olfactory sensory neurons. Research suggests the infection of nonneuronal support olfactory cells is responsible for anosmia in COVID-19 patients. This is good news as it indicates that it is unlikely that SARS-CoV-2 infection will cause permanent damage to the olfactory pathway circuits.6
The data from research indicates that COVID-19 related anosmia may arise from temporary loss of function of the supporting cells in the olfactory epithelium, which results in the impairment of olfaction. The researchers do not fully understand why olfactory impairment occurs.6,7
It is also suggested that COVID-19 anosmia occurs with the increase in the levels of interleukin-6 (IL-6), an important pro-inflammatory cytokine which leads to inflammatory damage to the olfactory epithelium. It is suggested that an inflammatory cytokine environment in the nasal cavity would also potentially affect olfactory neuronal function, as in rhinosinusitis.5
Impact of altered smell and taste
Burges Watson et al. examined the feedback from over 9,000 individuals who experienced altered smell and taste following COVID-19 infection. The loss of taste and smell associated with COVID-19 led to severe disruption to daily life that impacted on psychological wellbeing, physical health, relationships and sense of smell.8
Other reported symptoms include reduced desire and ability to eat and prepare food; weight gain or weight loss and nutritional insufficiency; loss of pleasure in food, eating and social engagement; altered intimacy and an altered relationship to self and others.8
It is very likely that many individuals would rank their sense of sight as far more important than their sense of smell.9
However, when you read the feedback made by individuals who experienced loss of smell and taste in the research paper by Burges Watson et al. - Altered smell and taste: anosmia, parosmia and the impact of long Covid-19, I have no doubt that you soon realise how important smell is.
For example, many individuals who experience loss of smell described food as being bland and unappetizing, this had a major impact on appetite, enjoyment, fullness and satiety. Dining out with friends and other people is an important daily pleasure and form of social bonding; however, impaired sense of smell and taste means that it is no longer enjoyable.8
The sense of smell also plays an important role in the way we interact with our environment, to other people and places and to ourselves. The feedback from those experiencing anosmia found that their relationship to the world, self and others had changed.8
I really need to share some of the comments so that you truly understand how stressful it must be to experience anosmia:
The world is very blank. Or if not blank, shades of decay. I feel alien from myself. It’s also kind of a loneliness in the world. Like part of me is missing as I can no longer smell and experience the emotions of everyday basic living. Detached from normality. Lonely in my body. It’s so hard to explain.8
Another person explained:
You feel so detached from reality when you can’t smell your surroundings.8
Sensory confusion was also very common:
Wine smells like sewage. Prosecco is even worse.8
or
Poo now smelled better than coffee.8
Body odour plays a very important role in establishing social bonds and in the way we develop close and intimate relationships. It is therefore not surprising that so many people experiencing anosmia following COVID-19 infection were concerned about not being able to smell their partner.8
I can’t smell my boyfriend’s natural scent, which makes me feel more distant from him. Like he is a stranger. I used to feel comforted being able to smell him while cuddling. Worse is that his kisses taste really bad to me know, so I avoid that, but I haven’t told him because I don’t want to hurt his feelings. Also, I am constantly worried that I smell bad myself and it makes me feel very insecure.8
or
The worst bit is not knowing if I smell. It makes me really self-conscious. If we get intimate, I can’t get lost in the moment anymore because I’m constantly worried that I smell bad myself and it makes me very insecure.8
The loss of smell not only affected romantic and sexual relationships, the inability to smell your own body odour creates a sense of anxiety about one’s body odour not being socially acceptable. This results in a sense of paranoia for some who felt the need to shower frequently and multiple change of clothing throughout the day, constant cleaning and frequent deodorising.8
This very detailed report gives us a very clear understanding into the challenges associated with loss of smell and taste or distorted sense of smell associated with COVID-19.
In conclusion, the following comment highlights the profound the impact on one’s mental wellbeing:
I’m losing hope and I’ve never been more depressed in my life. Will I ever get better? This has left me so low in mood. It’s really quite debilitating – physically, mentally and professionally. I’m 6 months in and losing hope.8
Burges Watson et al point out that until now health care professionals had overlooked the seriousness of smell and taste loss and as a result of the serious impact that COVID-19 is having on the senses now means we may see more research in developing strategies to manage the impact of sensory disruption.
Therapies for smell disorders
Research from the University of Cincinnati has suggested common coping mechanisms that help COVID-19 patients deal with a loss of smell and the impact that this has on the sense of taste. To compensate for the loss of taste, patients ate food with distinct textures such the different textures associated with fruits such as strawberries or apples. Patients also enjoyed cold drinks and carbonated drinks which would provide different sensation and texture.10
Olfactory training
Neta et al. state that olfactory training is considered one of the only current therapeutic strategies for treating post-viral olfactory loss.5
Olfactory training involves repeated daily exposure to a range of odorants.
Phenyl ethyl alcohol (from rose), eucalyptol (from eucalyptus or rosemary), citronella and eugenol (from clove bud) are four of the six odours that have been used to improve olfactory loss after training for 12 weeks or more.5
My suggestion is to use a rich floral such as ylang ylang or rose, a spicy aroma such as clove bud, a eucalyptol-rich oil such as rosemary or eucalyptus, and a rich lemon-scented oil such as lemon, lemon myrtle or citronella.
It is recommended that the olfactory training be done with each oil for 20 seconds, twice a day for at least 3 months as a treatment for anosmia associated with COVID-19.
While the efficacy of olfactory training is disputed, a systematic review supports the use of olfactory training for all patients with a loss of smell.5
It is also noted that the Rhinology Society recommend olfactory training for patients who complain of hyposmia or anosmia for more than 2 weeks.11
It is highly recommended that smell training be considered as a treatment. Smell training has no known side effects and is low cost.
Other options investigated for olfactory dysfunction included:
Zinc
Some reports suggest that zinc deficiency can cause dysfunction in smell and taste. One clinical trial involving patients with COVID-19 who received zinc therapy experienced significantly less olfactory recovery time.5
Vitamin A
Retinoic acid which is a metabolite of vitamin A is reported to promote olfactory neurogenesis due to its ability to regenerate the olfactory neuroepithelium. However, another randomised, double-blind, placebo-controlled clinical trial evaluating the oral administration of 10,000 IU of vitamin A per day for 3 months in patients with post infectious olfactory dysfunction showed no difference between the treatment and control group.5
Alpha-lipoic acid (ALA)
According to previous studies, alpha-lipoic acid may decrease ACE2 activity after SARS-C0V-2 replication and may also lead to the suppression of inflammatory cytokines. While an uncontrolled study found that 600 mg/day of ALA for an average of 4-5 months resulted in a moderate improvement in smell in 61% of the participants involved in the study, its use may be associated with neurological side effects including headache, dizziness and confusion. The British Rhinological Society do not recommend ALA for a patient with loss of smell as an isolated symptom for more than 2 weeks or following resolution of any other COVID-19 symptoms.5,12
Omega 3 fatty acids – it is reported that omega-3 supplementation may aid in the recovery after post-viral olfactory loss, although this has not been formally tested in post-COVID-19 patients. It is believed that omega 3 fatty acids may act through neuro-regenerative and anti-inflammatory mechanisms, which helps the olfactory nerve to heal and may also serve as an adjuvant therapy in olfactory training.5
Use of corticosteroids
Neta et al. state that corticosteroids have a very important role in the management of patients with SARS-CoV-2 who need mechanical ventilation but may also be effective in relieving the symptoms of anosmia and dysgeusia.5
Corticosteroids have been considered as a treatment for the olfactory loss in the past; however, a recent report indicates that there is no evidence that any kind of corticosteroid treatment is beneficial.1
Neta et al. also reported that patients who have anosmia as a result of COVID-19 should avoid oral or topical corticosteroids as there is no robust evidence to demonstrate any benefits over their potential risks.5
However, another study by Singh et al. found that olfactory and gustatory functions improved significantly in patients with COVID-19 after receiving nasal spray of fluticasone and oral triamcinolone after one week.13
References
1. Huart C et al. Systemic corticosteroids in coronavirus disease 2019 (COVID-19)-related smell dysfunction: an international view. International Forum of Allergy & Rhinology. 2021;11(7):1041-1046. doi:10.1002/air.22788
2. University of East Anglia, Smell training, not steroids, best treatment for COVID-19 smell loss, research finds. Apr 26, 2021, downloaded on 3 Nov 20221 from https://www.sciencedaily.com/releases/2021/04/210426140845.htm
3. Renaud M et al. Clinical outcomes for patients with anosmia 1 year after COVID-19 diagnosis. JAMA Network Open. 2021;4(6):e2115352. doi:10.1001/jamanetworkopen.2021.15352
4. Virginia Commonwealth University, Those under 40 are more likely than older adults to recover COVID-related smell and taste loss, study finds. Oct 5, Sep 2021, downloaded on 3 Nov 2021 from https://www.sciencedaily.com/releases/2021/10/211005124655.htm
5. Neta FI et al. Pathophysiology and possible treatments for olfactory-gustatory disorders in patients affected by COVID-19. Current Research in Pharmacology and Drug Discovery. 2021: 1000035. doi:10.1016/j.crpar.2021.100035
6. Jiang K, How COVID-19 causes loss of smell. Downloaded on 3 Nov 2021 from https://hms.harvard.edu/news/how-covid-19-causes-loss-smell
7. Brann DH et al. Non-neuronal expression of SARS-CoV-2 entry genes in the olfactory system suggests mechanisms underlying COVID-19-associated anosmia. Science Advances. 2020:6:eabc5801, 31 July 2020.
8. Burges Watson DL. Et al. Altered smell and taste: anosmia, parosmia and the impact of long Covid-19. PLoS ONE 2021;16(9):e0256998. doi:10.1371/journal.pone.0256998
9. University of York, Nov 5, 2018. Is there a universal hierarchy of human senses? Downloaded on 4 Nov 2021 from https://www.sciencedaily.com/releases/2018/11/181105160852.htm
10. University of Cincinnati, Research examines coping mechanisms for loss of smell from COVID-19. Oct 25, 2021, downloaded on 3 Nov 2021 from https://www.sciencedaily.com/releases/2021/10/211025113738.htm
11. Hummel T et al. Position paper on olfactory dysfunction. Rhinology – Official Journal of the European and International Societies. 2017;54(Supplement 26).
12. Hopkins C et al. Management of new onset loss of sense of smell during the COVID-19 pandemic – BRS concensus guidelines. Clinical Otolaryngology. 2021;46:16-22. Doi:10.1111/coa.13636
13. Singh CV et al. The outcome of fluticasone nasal spray on anosmia and triamcinolone oral paste in dysgeusia in COVID-19 patients. American Journal of Otolaryngology. 2021;42(3):102892. doi:10.1016/j.amjoto.2020.102892
