By Min Zan
Our sense of smell might not always get the attention it deserves, but recent events have made us realize just how vital it is. The ability to smell is not something we often think about, but when Joanne Hort, a professor from New Zealand, lost her sense of smell due to COVID-19, she discovered how crucial it is in her life. Like Joanne, many people around the world have experienced a disruption in their sense of smell because of the virus. While most recover quickly, for some, it can take several months. As Professor Evan Reiter from the Smell and Taste Disorders Centre points out, this loss, known as anosmia, has drawn attention to a sense that was once considered of little importance. In reality, our sense of smell plays a significant role in our daily lives, influencing our survival instincts, our food preferences, and even our emotional connections. Now, let’s explore the importance of our sense of smell and how to protect it.
“Once thought of as trivial, we now know our sense of smell is super important”
You probably get your eyes tested to protect your sight, maybe have a yearly hearing test to check your ears – but, protecting your nose… eh? However, as many of us have suffered or are suffering a disruption in our ability to smell thanks to COVID-19, we’re starting to appreciate just how important this ‘forgotten’ sense is – and why we should all be doing more to keep it healthy.
Just three days after being diagnosed with COVID-19 in September 2022, Joanne Hort realized she’d lost her sense of smell when she couldn’t taste some orange juice. “I panicked and ran to the bathroom and started trying to smell my perfume, but there was nothing,” says the academic from Palmerston North, New Zealand. Hort’s experience is now quite a common story, but what makes this tale different is that she doesn’t have a prevalent job. She’s a professor at New Zealand’s Massey University working in the field of sensory perception, so her sense of smell is integral to her career. “The idea that it might be gone or diminished was terrifying,” she says. “I started smelling everything I could to try and kick-start its return, but it took over six months for it to return properly.”
Around 86 per cent of people who have had COVID-19 experience a change in their sense of smell. For most, it’s short-lived but for one in every five, particularly the over-40s, the damage takes over six months to resolve. “And that’s a lot of people given the millions that have been afflicted with COVID-19,” says Professor Evan Reiter, medical director of the Smell and Taste Disorders Centre at Virginia Commonwealth University in the US. This epidemic loss, a condition known in medical terms as anosmia, has focused attention back on the sense that biologist Charles Darwin once described as “of extremely slight service to mankind”.
Almost 150 years after he said that we now know that Darwin was wrong – very wrong. “Research has discovered more than 600 genes in the human body associated with the sense of smell,” explains sensory expert Professor Eugeni Roura from Australia’s University of Queensland. “That’s around three per cent of the whole genome associated with just one system. That’s huge and shows that the sense of smell is actually immensely important to the human body.”
Let’s start again with the fact that smell can help keep us alive by alerting us to dangers such as food that might make us sick or the threat of fire, and it does this very quickly. Odour signals reach the brain within 100-150 milliseconds of inhalation – and recent research from Sweden found we process unpleasant or dangerous smells even faster than innocuous ones.
“But smell also helps create the flavour of food and plays a role in controlling the variety of our diet and the nutrients we consume,” says Professor Hort. “It’s linked to emotion and memory.” It may even be why you picked your partner as we subconsciously use smell to help find mates who have different immune systems to our own.
So how do we smell? It happens when odour molecules in the air hit nerves in the lining of the nose. These send signals to the olfactory organ, the part of the brain that interprets smell, which scours our memory to determine what the smell is – and if it’s good, bad, or indifferent.
The olfactory organ makes up around five per cent of the human brain. It’s estimated that it can distinguish between a million different odours. Each of us has a unique sense of smell and the strength of our unique smell is related to the genes you inherit from your parents which determine which smell receptors (detectors) are expressed in the nose.
Other factors further determine how sensitive your sense of smell is. Women generally have a stronger sense of smell than men, while damage from air pollution means people who live in highly polluted cities have a less sensitive sense of smell than those in rural areas.
“We also know the sense of smell declines with age,” says Professor Hort. “And if you’ve damaged your nose through a head injury, illness, or inhaling something that causes irritation, your sense of smell can also be negatively affected.”
Protecting your nose from such damage is therefore the first step in keeping your sense of smell thriving. Avoid inhaling strong scents like bleach or other chemicals. If you have a long-term condition like rhinitis, speak to your GP about nasal sprays that might help dampen down the inflammation.
Then, keep your nose busy. “The sense of smell is a bit like a muscle, you can train it to become stronger by exercising it,” says Professor Roura.
Here’s how to give yours a workout.
Make smell a primary sense
During the day we tend to focus more on our other senses like taste or sight, but start using smell, too. Sniff vegetables and fruit as part of determining ripeness before you buy them, focus on the different notes in the perfume you wear, or identify different flowers in your garden by scent alone.
Seek out new scents
The more different smells you expose your nose to, the better. “When I work with smell experts, they literally smell everything they find interesting,” says Professor Roura, laughing. “Travelling with them is a bit of a nightmare, as it takes ages to get anywhere as they keep sniffing things.”
Feed your nose
Just like the rest of your body, your olfactory system needs a good mix of nutrients to perform optimally – deficiencies in vitamin D, vitamin B12, and zinc have all been linked to a reduced sense of smell. But, also watch your fat intake. Research from Florida State University found that mice eating a high-fat diet had a reduced sense of smell – and fewer olfactory neurons – than those eating a less fatty diet.
Stay hydrated
“To smell effectively the mucosa of the nose needs to be in a good physiological state – and hydration plays a part in this. You don’t smell as well if your nose is dehydrated,” says Professor Roura.
Why COVID-19 damages the sense of smell
A reduction in the ability to smell is quite common with respiratory infections like cold, flu, and COVID-19, as mucus produced during such illnesses physically blocks smell molecules from reaching the nerves that interpret them. However, COVID-19 doesn’t just block the nerves. “It actually infects the neurons, leading to cell death – and this can go all the way up the brain,” says Professor Roura. “These cells then need to be renewed to restore the sense of smell – and that’s why recovery can take so much longer than with colds or flu.”
Research into how to tackle COVID-related smell loss is ongoing but one technique that is helping is smell training. Take four strong (but not harmful) scents – in studies they start with rose, clove, eucalyptus, and lemon– and sniff them. This is done twice a day and can stimulate the regrowth of the smell neurons in around three months. Ask your GP the exact protocol if you’re affected.
In brief, the sense of smell, often overlooked in the past, has proven to be incredibly important to our overall well-being. COVID-19 has brought this “forgotten” sense into the spotlight, as many have experienced disruptions in their ability to smell. Research has revealed that our sense of smell is linked to our survival instincts, food preferences, emotions, and even mate selection. It is a crucial part of our lives, and we should take steps to protect and strengthen it. By avoiding strong, irritating scents, staying hydrated, and actively engaging our noses through smell exercises, we can maintain a healthy sense of smell. So, let’s not underestimate the power of our sense of smell and continue to appreciate its significance in our lives.
Reference: Reader’s Digest May 2023
