First coffee, then other smells were missing. How to retrain your brain
Losing a sense of smell can be an alarming signal of other potential diseases down the track, including mental decline. But there are ways to reverse the loss.
My first sign of smell loss came with a morning espresso. I’d normally pop out of bed to make it and then slip back under the covers, savouring the scent as I listened to a podcast or read the newspaper.
Earlier this year, however, I realised that the fumes no longer hit me with the same intensity. I wondered if it could be blamed on the blend I’d been using, but a change of brand did no good. The more I puzzled over the loss, the more I noticed that other aromas were missing too. From the blossom in my local park to the welcoming scent of a chicken roasting in the oven, the incidental fragrances that had once coloured my “smellscape” seemed to have faded to the point of non-existence.
As a science writer, I was alarmed to discover that this sensory loss may have some serious long-term consequences. I am just 39, at the cusp of middle age, but poor smell is associated with worse mental health and impaired memory across one’s lifespan; there is even some evidence linking it to an increased risk of Alzheimer’s. So I was curious to discover that the damage can often be reversed through what’s known as “smell training”. By consciously and deliberately exposing ourselves to new scents, our sense of smell can become stronger, with knock-on benefits for our brains.
Lovers of French literature may not be surprised by these findings. Marcel Proust immortalised the powerful link between the nose and the brain in Swann’s Way, the first part of his novel In Search of Lost Time, in which a madeleine brings a rush of memories from the protagonist’s childhood. “Smell and taste live on for a long time, alone, more fragile but more enduring, more immaterial but more persistent, more faithful,” he wrote, “bearing unfalteringly on their almost impalpable little drop, the vast edifice of memory.”
The latest neuroscience tells us why that is. Signals from other senses — such as sight, hearing or touch — pass through a neural hub known as the thalamus before being passed on to the relevant regions of the cortex to be processed. Smells, on the other hand, bypass this relay station. Instead their messages move straight from the olfactory nerve’s receptors in the nose to the olfactory bulb, a brain region lying just above the nasal cavity that makes sense of the incoming information. Importantly, the olfactory bulb sits right next to brain regions that process emotions and memory, allowing an evocative scent to produce those intense “Proustian moments”.
We may not fully appreciate how profoundly this influences our inner lives until it is gone. As we saw during the Covid pandemic, viral infections can cut the connection between the nose and the brain. The olfactory nerve can also be damaged by chemical contaminants, including air pollution and cigarette smoke that irritate the nerve’s receptors and its surrounding tissue, by physical injury and by the development of nasal polyps that block the air flow. Like many organs, the nose can also suffer general wear and tear as we age. According to the US National Institutes of Health, about 23 per cent of the population have a measurable impairment by the age of 40, and that figure rises to 39 per cent for those aged 80 and above.
The most obvious consequence may be low mood; many studies have now linked smell loss with depression. Smell is, after all, a source of daily pleasure that we often take for granted. I had never noticed just how much I appreciated the aroma of my morning espresso, for instance, until I could no longer experience it. Such small delights can add up over the day, and our world feels much flatter without them.
Even more worrying are the effects on our general mental functioning. A study from 2019 found that people with a poorer sense of smell also performed worse on five different tests measuring attention, processing speed, verbal fluency, learning and memory. This appears to be true at any age group, but it may be especially important in middle and later life, as we experience the natural decline that can eventually lead to dementia. The worse your sense of smell at the start of old age, the greater your chances of developing Alzheimer’s in the years ahead. Remarkably, sniff tests prove to be a better predictor of who will go on to develop the disease than the standard cognitive assessments used to identify people who may be at risk.
The long-term effects of olfactory loss are visible in scans of the brain. Without signals from the nose, the regions associated with emotion, memory and learning have lost a serious source of stimulation, and so they begin to atrophy. It seems to be a case of use it or lose it.
For those of us who are struggling to smell the roses, there is plenty of room for hope. By putting the nose through a daily workout, many people have been able to reverse the damage and regain the lost sense. “The olfactory nerve is very neuroplastic,” David Vance, a psychologist at the University of Alabama at Birmingham, told me as I embarked on this journey. “It’s evolved to regenerate itself.”
The first scientific trial was conducted in 2009 by Thomas Hummel at the Dresden University of Technology. He selected four intense odours — originating from clove, eucalyptus, rose and lemon — that are thought to activate the majority of the nose’s receptors. The participants were asked to sniff each scent for about ten seconds in the morning and ten seconds at night. After 12 weeks many of them had already shown a notable improvement in their nose’s sensitivity.
This success story has now been replicated many times. Crucially, the olfactory enhancement is often accompanied by improved performance on cognitive tests.
Having read about these exciting results, I was keen to try smell training for myself. At the beginning of April I purchased my first kit from Amazon. I chose one produced by a company called Hion that costs £16, but there are many alternatives. It contains six tubes that look very much like the inhalers you might buy to clear nasal congestion. Together they cover the four essential oils tested in Hummel’s trial, as well as mint and grapefruit. Knowing how easy it is to forget the things that are good for us, I keep the kit on my beside table as a reminder to sniff each inhaler for ten seconds in each nostril as soon as I wake, and in the evening as I prepare for bed.
The experts advise that we focus intensely on the sensations evoked by the odour. “Feel it or engage with it in the same way you might look at a picture, and try and call on your memory for things that you might associate with it,” says Chrissi Kelly, a founder of the CKOS network for people with smell loss.
Over the past two months I have found that I am already much better able to distinguish the different odours. Like other health regimes, however, you may be rewarded for long-term dedication. In one study people saw the greatest benefits after a year of training.
Inspired by my early success, I’ve looked to give my nose — and my little grey cells — as much stimulation as I can find. I’ve purchased numerous other essential oils — the kind you might buy in any health food shop — which I keep on my work desk to sniff whenever I’m feeling a little bored. In the past I would typically ignore the flowers in the local park; now I actively seek them out. And when I’m in the kitchen I’ll inhale the aromas that are readily available in my spice rack, and I pay greater attention to the fumes emanating from the boiling pots and pans.
I now consider smell training to be an essential part of my routine. I find it to be pleasantly meditative, leaving me mentally grounded in much the same way as my daily yoga. And while I cannot say that I’ve noticed a huge leap in brainpower, I am optimistic that I am protecting my brain from future decline.
This morning I made my espresso as normal and sniffed the cup hopefully. For the first time since I began my smell training, the aroma hit me hard. I couldn’t help but smile when I realised that I had, quite literally, learnt to wake up and smell the coffee, and I shall never take my nose for granted again.
David Robson is a science writer and the author of The Laws of Connection: 13 Social Strategies That Will Transform Your Life (Canongate).
The Times
To join the conversation, please log in. Don't have an account? Register
Join the conversation, you are commenting as Logout