What happens when you lose your sense of smell?
Imagine a world where the fragrance of fresh flowers, the aroma of a morning coffee, or the scent of a loved one's perfume is dulled or non-existent. Our daily sensual experiences in such a world would be constantly flattened and dull. For some individuals, this is a reality and anosmia, the loss of the sense of smell, can profoundly impact one’s quality of life. Of course, there are the obvious downsides to losing your sense of smell that we all recognise – interference with your ability to taste foods or to detect dangers like spoiled food or fire. But the problems of a diminished or absent sense of smell go far beyond these commonly recognised issues.
Our sense of smell was once derided by Charles Darwin as being “of extremely slight service, if any” to humans and Sigmund Freud even drew the conclusion that a loss of interest in odours was simply a natural progression in the evolution of developing an upright posture and, subsequently, civilised behaviour [1]. This disinterest in our sense of smell from the medical and scientific communities largely persisted until the 1990’s, with the discovery of odour receptors, which led to the 2004 Nobel Prize in Medicine for Richard Axel and Linda Buck. It has been commonly accepted that humans have poor olfactory abilities compared with other animals but this really is a myth, propagated by some poor science, in which inappropriate comparisons were made [2]. In fact, some studies now suggest that humans can distinguish between – wait for it – more than a trillion odour compounds [3] and in some cases, humans outperform dogs and rodents in the realm of detecting odour.
The mechanisms behind our sense of smell are perhaps a subject for a future blog but here, I want to talk about what happens when you lose your sense of smell and whether you can regain it. Over the past few decades, the importance of our sense of smell has emerged and is now a vibrant area of research, not only for physiologists and geneticists but for clinical psychologists because it turns out that experiencing multiple fragrances is absolutely central to our quality of life and wellbeing.
In fact, loss of smell is associated with many mental health conditions, including Parkinson’s, Alzheimer’s, schizophrenia, dementia, autism, anxiety and depression [4, 5]. COVID-19 is a well-known, recent cause of anosmia (although other viral infections can also be a cause) and when it is prolonged, there are significant negative impacts on quality of life [6]. Some clinics are now using the loss of olfactory ability as a diagnostic tool for early detection of degenerative diseases, while others are now using so-called “olfactory enrichment” – the regular exposure of subjects to multiple odours – to treat some of these conditions. One study even showed that overnight exposure to fragrances, while sleeping, improved performance in standardised memory tests by 226% in healthy adults over the age of 65 years [7].
There are several causes of anosmia. Some of the most common include:
Nasal Congestion or Blockage: Conditions like sinus infections, colds, or allergies can temporarily affect your ability to smell.
Neurological Disorders: Certain conditions, like Alzheimer’s or Parkinson’s disease, can be preceded by a loss of olfactory ability, which continues throughout the disease progression.
Head Trauma: A severe blow to the head can damage the olfactory nerves.
Viral Infections: Some viral infections, notably COVID-19, have been known to cause temporary or prolonged loss of smell.
Aging: The sense of smell naturally diminishes with age.
Exposure to Toxic Chemicals: Certain chemicals can damage the olfactory system.
I recently experienced a 24-hour loss of smell through nasal congestion and (I think, though I have no scientific evidence) use of a nasal decongestant spray and that – let me tell you - for a perfumer, was a scary experience! My sense of relief upon regaining my olfactory ability was immense and I have since decided to put up with the congestion rather than risk the possibility of damage!
But for those with less control over their loss of smell, can anything be done? Treatment for full anosmia will depend on its causes. If the anosmia is due to an infection or allergy, treating those conditions may help restore the sense of smell. For other causes, including aging or specific degenerative conditions, smell training, which involves sniffing a variety of strong odours daily to stimulate the olfactory nerves, can be helpful and there is scientific proof that it will alter brain structure [7,8]. The University of North Carolina (UNC) School of Medicine has a specialised Covid Recovery Unit and, while I have no particular evidence as yet that this would be effective for COVID-19 sufferers, they offer the following advice to help with recovery of one’s sense of smell [9], which certainly fits with the general research literature on smell training:
Smell Retraining
Altered smell and loss of smell is common after COVID-19. Smell retraining may assist with recovery. For smell retraining there are 4 essential oils that are used to assist in possibly restoring sense of smell. The essential oils are: rose, citronel (citrus or lemon), eucalyptus (menthol), and cinnamon.
In order to perform smell retraining, you should smell each essential oil twice a day for 6 weeks. Steps are as follows:
1. Place a few drops of the essential oil on a cotton ball or pad and let it sit for a minute or two.
2. Bring the pad within an inch of your nose and inhale through your nose slowly and naturally. Visualize what you’re trying to smell, either by looking at a picture or imagining with your eyes closed.
3. Move the pad away, and then repeat several times with the same oil.
4. Repeat this process with each essential oil taking a few minutes break between each separate oil.
Try not to get discouraged. You may not smell anything at first, but that is ok. It may take time before you begin to smell anything.
Such a regimen appears to be consistent with what we now know about recovering our sense of smell. Inxhale’s “Alert” inhaler closely matches the essential oils recommended by UNC for smell training, while the “Calm” inhaler contains a second, complimentary set of essential oils that will amplify olfactory enrichment. Whether or not these products are your solutions, I cannot stress too highly the importance of our sense of smell in our general health and well-being and I strongly recommend that it is not overlooked.
References
[1] “Human olfactory communication: current challenges and future prospects”, S.C. Robert, J. Havliček and B. Schaal, Philos Trans R Soc Lond B Biol Sci., 2020 Jun 8; 375(1800)
[2] “Poor human olfaction is a 19th-century myth”, J.P. McGann, Science, May 2017, 356, 597
[3] “Humans can discriminate more than 1 trillion olfactory stimuli”, C. Bushdid, M.O. Magnasco, L.B. Vosshall and A. Keller, Science, 2014, Vol. 343, pp 1370-1372
[4] “Odorants: a tool to provide nonpharmaceutical intervention to reduce anxiety during normal and pathological aging”, B. Ballanger, K.G. Bath, N.Mandairon, Neurobioogy of Aging, 2019, 82, pp18-29
[5] “Effect of intensive olfactory training for cognitice function in patients with dementia”, H. Cha, S. Kim, H. Kim, G. Kim and K-Y. Kwon, Geriatrics Gerontology International, 2022, 22, pp5-11.
[6] “Impact of smell loss on the quality of life and adopted coping strategies in COVID-19 patients”, S. Elkholi, M. Abdelwahab and M. Abdelhafeez, 2021, European Archives of Otorhinolaryngology, 2021, 278(9), pp3307-3314
[7] “Overnight olfactory enrichment using an odorant diffuser improves memory and modifies the uncinate fasciculus in older adults”, C.C. Woo, B. Miranda, M. Sathishkumar, F. Dehkordi-Vakil, M.A. Yassa and M. Leon, Frontiers in Neuroscience, 17:1200448
[8] “Smell training improves olfactory function and alters brain structure”, S.Al Aïn, D. Poupon, S. Hétu, N. Mercier, J Steffaner, J. Frasnelli, Neuroimage, 1029, 189, pp45-54
[9] UNC Covid Recovery Unit: https://www.med.unc.edu/phyrehab/wp-content/uploads/sites/549/2023/01/COVID-Resources-smell-taste.pdf
