You can train your nose – and 4 other surprising facts about your sense of smell
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<p><em><a href="https://theconversation.com/profiles/lynn-nazareth-1650578">Lynn Nazareth</a>, <a href="https://theconversation.com/institutions/csiro-1035">CSIRO</a></em></p>
<p>Would you give up your sense of smell to keep your hair? What about your phone?</p>
<p>A <a href="https://pmc.ncbi.nlm.nih.gov/articles/PMC8946147/">2022 US study</a> compared smell to other senses (sight and hearing) and personally prized commodities (including money, a pet or hair) to see what people valued more.</p>
<p>The researchers found smell was viewed as much less important than sight and hearing, and valued less than many commodities. For example, half the women surveyed said they’d choose to keep their hair over sense of smell.</p>
<p>Smell often goes under the radar as one of the least valued senses. But it is one of the <a href="https://royalsocietypublishing.org/doi/10.1098/rsob.200330">first sensory systems vertebrates developed</a> and is linked to your mental health, memory and more.</p>
<p>Here are five fascinating facts about your olfactory system.</p>
<h2>1. Smell is linked to memory and emotion</h2>
<p>Why can the waft of fresh baking trigger joyful childhood memories? And why might a certain perfume jolt you back to a painful breakup?</p>
<p>Smell is directly linked to both your memory and emotions. This connection was first established by American psychologist <a href="https://www.jstor.org/stable/16002">Donald Laird in 1935</a> (although French novelist <a href="https://www.penguin.co.uk/articles/2020/07/more-than-cake-unravelling-the-mysteries-of-proust-s-madeleine">Marcel Proust had already made it famous</a> in his reverie about the scent of madeleines baking.)</p>
<p>Odours are first captured by special olfactory nerve cells inside your nose. These cells extend upwards from the roof of your nose towards the smell-processing centre of your brain, called the <a href="https://www.ncbi.nlm.nih.gov/books/NBK55972/">olfactory bulb</a>.</p>
<figure class="align-center zoomable"><a href="https://images.theconversation.com/files/640871/original/file-20250107-15-vili6v.jpg?ixlib=rb-4.1.0&q=45&auto=format&w=1000&fit=clip"><img src="https://images.theconversation.com/files/640871/original/file-20250107-15-vili6v.jpg?ixlib=rb-4.1.0&q=45&auto=format&w=754&fit=clip" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px" srcset="https://images.theconversation.com/files/640871/original/file-20250107-15-vili6v.jpg?ixlib=rb-4.1.0&q=45&auto=format&w=600&h=592&fit=crop&dpr=1 600w, https://images.theconversation.com/files/640871/original/file-20250107-15-vili6v.jpg?ixlib=rb-4.1.0&q=30&auto=format&w=600&h=592&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/640871/original/file-20250107-15-vili6v.jpg?ixlib=rb-4.1.0&q=15&auto=format&w=600&h=592&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/640871/original/file-20250107-15-vili6v.jpg?ixlib=rb-4.1.0&q=45&auto=format&w=754&h=744&fit=crop&dpr=1 754w, https://images.theconversation.com/files/640871/original/file-20250107-15-vili6v.jpg?ixlib=rb-4.1.0&q=30&auto=format&w=754&h=744&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/640871/original/file-20250107-15-vili6v.jpg?ixlib=rb-4.1.0&q=15&auto=format&w=754&h=744&fit=crop&dpr=3 2262w" alt="Diagram showing odour particles travelling through the nose into the brain." /></a><figcaption><span class="caption">Smells are first detected by nerve cells in the nose.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/sense-smell-detailed-illustration-olactory-region-1832630776">Axel_Kock/Shutterstock</a></span></figcaption></figure>
<p>From the olfactory bulb they form direct connection with the brain’s <a href="https://my.clevelandclinic.org/health/body/limbic-system">limbic system</a>. This includes the <a href="https://www.sciencedirect.com/science/article/pii/S1879729610001237">amygdala</a>, where emotions are generated, and the <a href="https://academic.oup.com/brain/article/133/9/2509/357465">hippocampus</a>, where memories are created.</p>
<p>Other senses – such as sight and hearing – aren’t directly connected to the lymbic system.</p>
<p>One <a href="https://www.sciencedirect.com/science/article/pii/S0028393203002161">2004 study</a> used functional magnetic resonance imaging to demonstrate odours trigger a much stronger emotional and memory response in the brain than a visual cue.</p>
<h2>2. Your sense of smell constantly regenerates</h2>
<p>You can lose your ability to smell due to injury or infection – for example during and after a COVID infection. This is known as <a href="https://link.springer.com/article/10.1007/s00441-020-03381-9">olfactory dysfunction</a>. In most cases it’s temporary, returning to normal within a few weeks.</p>
<p>This is because every few months <a href="https://www.nature.com/articles/s41593-020-0587-9">your olfactory nerve cells die and are replaced</a> by new cells.</p>
<p>We’re not entirely sure how this occurs, but it likely involves your nose’s <a href="https://www.cell.com/heliyon/fulltext/S2405-8440(24)05979-6">stem cells</a>, <a href="https://pmc.ncbi.nlm.nih.gov/articles/PMC2387238/#:%7E:text=When%20the%20olfactory%20nerves%20and,reestablish%20connections%20with%20the%20bulb">the olfactory bulb</a> and <a href="https://onlinelibrary.wiley.com/doi/10.1002/cne.23694">other cells</a> in the olfactory nerves.</p>
<p>Other areas of your nervous system – including your brain and spinal cord – cannot regenerate and repair after an injury.</p>
<p>Constant regeneration may be a protective mechanism, as the olfactory nerves are vulnerable to damage caused by the external environment, including toxins (such as cigarette smoke), chemicals and pathogens (<a href="https://academic.oup.com/jid/article/210/3/419/2908527">such as the flu virus</a>).</p>
<p>But following a COVID infection some people might continue to experience a loss of smell. Studies suggest <a href="https://www.sciencedirect.com/science/article/pii/S0092867421012824?via%3Dihub">the virus</a> and a <a href="https://www.science.org/doi/10.1126/scitranslmed.add0484">long-term immune response</a> damages the cells that allow the olfactory system to regenerate.</p>
<h2>3. Smell is linked to mental health</h2>
<p>Around <a href="https://journals.sagepub.com/doi/full/10.1177/1945892420946254">5% of the global population</a> suffer from anosmia – total loss of smell. An estimated 15-20% suffer partial loss, known as hyposmia.</p>
<p>Given smell loss is often a primary and long-term symptom of COVID, these <a href="https://www.nature.com/articles/s41598-024-53919-y">numbers are likely to be higher</a> since the pandemic.</p>
<p>Yet in Australia, the prevalence of olfactory dysfunction <a href="https://www1.racgp.org.au/ajgp/2021/september/an-approach-to-olfactory-impairments">remains surprisingly understudied</a>.</p>
<p>Losing your sense of smell <a href="https://academic.oup.com/chemse/article/doi/10.1093/chemse/bjab037/6342176">is shown to impact your personal and social relationships</a>. For example, it can mean you miss out on shared eating experiences, or cause changes in sexual desire and behaviour.</p>
<p>In older people, declining ability to smell is associated with a <a href="https://academic.oup.com/biomedgerontology/article/79/1/glad139/7207364?login=true">higher risk of depression</a> and <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0107541">even death</a>, although we still don’t know why.</p>
<h2>4. Loss of smell can help identify neurodegenerative diseases</h2>
<p>Partial or full loss of smell is <a href="https://www.sciencedirect.com/science/article/pii/S1474442217301230?via%3Dihub">often an early indicator for a range of neurodegenerative diseases</a>, including Alzheimer’s and Parkinson’s diseases.</p>
<p>Patients <a href="https://www.neurology.org/doi/abs/10.1212/wnl.0000000000001265">frequently report losing their sense of smell</a> years before any symptoms show in body or brain function. However many people are not <a href="https://onlinelibrary.wiley.com/doi/10.1002/9781118971758.ch18">aware they are losing their sense of smell</a>.</p>
<p>There are ways you can determine if you have smell loss and to what extent. You may be able to visit a formal <a href="https://www.epworth.org.au/our-services/rehabilitation/brain-injury-and-neurological-disorders/olfactory-impairment-clinic#:%7E:text=Epworth%20is%20the%20first%20rehabilitation,and%20associated%20changes%20in%20taste.">smell testing centre</a> or do a <a href="https://esurvey.uniklinikum-dresden.de/pub/index.php/678693">self-test</a> at home, which assesses your ability to identify household items like coffee, wine or soap.</p>
<h2>5. You can train your nose back into smelling</h2>
<p>“Smell training” is emerging as a <a href="https://link.springer.com/article/10.1007/s00405-024-08733-7">promising experimental treatment option</a> for olfactory dysfunction. For people experiencing smell loss after COVID, it’s been show to <a href="https://pmc.ncbi.nlm.nih.gov/articles/PMC9309586/">improve the ability to detect and differentiate odours</a>.</p>
<p>Smell training (or “olfactory training”) was first tested in 2009 in a <a href="https://onlinelibrary.wiley.com/doi/10.1002/lary.20101">German psychology study</a>. It involves sniffing robust odours — such as floral, citrus, aromatic or fruity scents — at least twice a day for 10—20 seconds at a time, usually over a 3—6 month period.</p>
<p>Participants are asked to focus on the memory of the smell while sniffing and recall information about the odour and its intensity. This is <a href="https://jamanetwork.com/journals/jamaotolaryngology/fullarticle/2782042">believed to help reorganise the nerve connections</a> in the brain, although the exact mechanism behind it is unclear.</p>
<p>Some studies recommend using a <a href="https://onlinelibrary.wiley.com/doi/10.1002/lary.20101">single set of scents</a>, while others recommend <a href="https://onlinelibrary.wiley.com/doi/full/10.1002/lary.25245">switching to a new set of odours</a> after a certain amount of time. However <a href="https://onlinelibrary.wiley.com/doi/full/10.1002/lary.26985">both methods show significant improvement</a> in smelling.</p>
<p>This training has also been shown to alleviate depressive symptoms and improve cognitive decline both in <a href="https://onlinelibrary.wiley.com/doi/full/10.1002/gps.4725">older adults</a> and those suffering from <a href="https://pubmed.ncbi.nlm.nih.gov/34749425/">dementia</a>.</p>
<p>Just like physiotherapy after a physical injury, olfactory training is thought to act like <a href="https://www.sciencedirect.com/science/article/pii/S0149763422003426#sec0005">rehabilitation for your sense of smell</a>. It retrains the nerves in your nose and the connections it forms within the brain, allowing you to correctly detect, process and interpret odours.<!-- Below is The Conversation's page counter tag. Please DO NOT REMOVE. --><img style="border: none !important; box-shadow: none !important; margin: 0 !important; max-height: 1px !important; max-width: 1px !important; min-height: 1px !important; min-width: 1px !important; opacity: 0 !important; outline: none !important; padding: 0 !important;" src="https://counter.theconversation.com/content/245366/count.gif?distributor=republish-lightbox-basic" alt="The Conversation" width="1" height="1" /><!-- End of code. If you don't see any code above, please get new code from the Advanced tab after you click the republish button. The page counter does not collect any personal data. More info: https://theconversation.com/republishing-guidelines --></p>
<p><em><a href="https://theconversation.com/profiles/lynn-nazareth-1650578">Lynn Nazareth</a>, Research Scientist in Olfactory Biology, <a href="https://theconversation.com/institutions/csiro-1035">CSIRO</a></em></p>
<p><em>Image credits: Shutterstock</em></p>
<p><em>This article is republished from <a href="https://theconversation.com">The Conversation</a> under a Creative Commons license. Read the <a href="https://theconversation.com/you-can-train-your-nose-and-4-other-surprising-facts-about-your-sense-of-smell-245366">original article</a>.</em></p>
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