Why COVID-19 can uniquely and suddenly impact a person’s sense of smell and consequently taste is not yet fully understood. Not everyone experiences loss of smell and taste as a symptom. In some that do, it might not last very long. Others are not so lucky.
The ZOE COVID symptom app reports that as many as one in 20 people who have had COVID suffer symptoms for more than eight weeks. Carl Philpott, a professor of rhinology and olfactology at the University of East Anglia and who set up the awareness charity Fifth Sense, reports that about 60% of those with COVID suffer smell/taste disturbances; of that 60% about 10% have persistent problems beyond four weeks.
“There’s a lot we don’t know,” added Dr Duika Burges Watson, who runs the Altered Eating Research Network at Newcastle University, which offers food solutions to people with smell loss. “What we do know is that smell and taste loss are very common symptoms of COVID. Based on conservative estimates, several million people have been affected by smell and taste loss, but most will recover within weeks.”
Burges Watson is academic advisor to AbScent, a charity also offering support to those who have lost their sense of smell and taste. In March last year, AbScent’s Facebook group page had about 1,000 members. It now has over 20,000.
The impairments caused by COVID can come in two ways. Some report a loss of smell and taste – called anosmia. Others experience parosmia, when the smell of certain things – or sometimes everything – is different, and usually unpleasant.
“Initially you tend to find most people will experience anosmia, or a complete loss of smell. It may come back. Or it may be diminished in the form of hyposmia, a slightly reduced sense of smell. And then it can turn to parosmia. We've got cases of people in the Facegroup group who have had parosmia since March and it's still going,” Burges Watson elaborated. “Parosmia causes pretty much everything to taste revolting."
What tastes and flavours stand out?
Burges Watson identifies certain ‘trigger foods’ among parosmia sufferers which become distorted and unpleasant. These are ones normally associated with rich smells and flavour such as coffee, onions, garlic, anything roasted or toasted, chocolate, peppers, citrus and apples.
"Interestingly, people describe a lot of their food smelling and tasting like faeces but they will often find that faeces doesn't smell bad. So the categories about what we think is OK and what isn't OK get mixed up. Suddenly poo smells are acceptable; and food smells like poo."
Meat tends to become intolerable and parosmia sufferers will often become vegetarian. ‘Safe’ foods tend to be plainer ones such as dairy and cheese.
Anosmia brings different challenges. Sufferers tend to complain that foods simply don't taste of much and that eating becomes a thin, boring experience which lacks enjoyment. They can often only experience tastes that are highly salty or sweet, which can lead to a health and nutrition impact. “Some people end up eating more and are putting on lots of weight because it's almost like they are chasing the flavour and the sensation that they used to get,” said Burges Watson. Others end up eating a lot less, almost developing eating disorders, owing to the tasteless experience that eating becomes.
There’s evidence parosmia is affecting young people and healthcare workers, according to Burges Watson, though not disproportionately. Other facets unique to COVID continue to emerge. Reading University has recently identified a smell lock, or perseveration, in COVID cases where a smell becomes stuck in a person's nose for the rest of the day. There is also evidence that COVID might effect trigeminal input, impacting not just smell and taste, but a person’s ability to experience the burn of chili or the zing of ginger.
The ‘underrated’ sense
Many are able to shrug off smell and taste loss in less severe and short-lived cases. But it can have a deep impact on a person's experience of food, and their pleasure in general, added Burges Watson’s colleague from Northumbria University, Professor Vincent Deary. “Once your relationship to food is disrupted, a major source of daily pleasure and joy goes out of your life and that has a major impact on their mood, sociability, and their ability to join in events.
“For many, a whole dimension of the world is suddenly gone. Some people describe it as a sense of unreality, of disconnection, of not actually being in the world. That can be quite a lonely, isolating and sometimes terrifying sensation.”
Charles Spence is an Oxford academic and world expert in multisensory perception. His latest book Sensehacking explores the remarkable ways we can use our senses to lead richer lives.
He agrees that smell and taste are undervalued senses, which when lost can often have a profound impact on a person. “In the early days of the pandemic there were reports of patients complaining of a loss of taste in food and it wasn't really taken seriously,” he said. “But it appears to be one of the most common symptoms of COVID. It surprised me it took so long for it to become a recognised symptom. Imagine if people were losing their vision or hearing; we'd have known about it much sooner." It’s ironic, he adds, as suicide statistics actually suggest that those who lose their sense of smell are worse off than those who lose their sight.
Are there any implications in this for the food industry?
What opportunities, if any, can the food industry possibly eek out of all of this? Much probably depends on how large and long-lasting the problem of COVID’s impact on smell and taste proves.
Smell and taste tend to return back to normal among those who have experienced it as a symptom of COVID. But, again, it’s too early to tell for sure. According to Carl Philpott at Fifth Sense, the natural history of all smell dysfunction viruses suggests that one in three will get better over three years.
The pandemic has, however, shone a light on the problems faced by all those consumers whose experience of food is diminished by lack of sense of smell.
AbScent estimates around 5% of people in the UK are affected by smell loss – that’s around 3.25 million people – with an additional 15% affected by a reduced sense of smell (hyposmia). Some loss of taste and smell is also natural in older people, especially after age 60, and an ageing populatoin is a growing demographic.
Burges Watson believes the pandemic has also exposed the lack of sensory knowledge among healthcare professionals. There is therefore an opportunity for the food industry to work with health professionals to help deliver more fulfilling taste experiences for these people, she believes.
“We hope to put the issue of altered eating with altered sensory experience from COVID and all other areas much more firmly on the map,” she said. “I think there's a really important role for people who are working with flavour to help us out and help us develop foods that are going to be tolerable.
“Some with parosmia, for example, find that cinnamon and vanilla can mask off flavours. But we're still not entirely sure what works and everybody seems to be slightly different.”
‘Nothing stimulates like texture’
Nathaniel Davis, a specialist flavour and fragrance lecturer based at the Université Côte d’Azur in world perfume capital Grasse, believes that there’s scope for the industry to develop new tastes and, in particular, textures that can potentially allow sufferers from smell and taste loss a more fulfilling and nutritious eating experience.
“What all consumers with this anosmia would like is good quantity of food with a pleasant persistent flavour,” he said. “As this can’t be perceived by them, the texture is important. Nothing stimulates like texture. A firmer texture may help to extend time in mouth and extend the taste.”
Crispy foods too, he says, can spread successfully through the mouth with a noisy and stimulating high intensity. Good options here include crisps/chips, biscuits/cookies, toast, breakfast cereals, and French fries. Healthier options carrying the ‘crunch’ impact might include ice, celery, broccoli, carrots, cucumber and nuts.
“Contrasting features of foods are also important. Just like a story or a film we like changes, twists in plot – every eating experience is filled with key themes such as aroma, mid mouth, texture and aftertaste. Often the meals and products we like best have flavour or texture contrasts within them. Like for example a nutty, crispy texture with a soft gooey filling.”
Despite the aforementioned evidence that the virus also targets the trigeminal nerve, food manufacturers should still explore spice and heat, he reckons. “Trigeminal triggers rewards are so high as they provide us with pain and pleasure.” He recommends exploring the use of texture and touch, with ice and heat or chili and wasabi.
“The ‘thrill’ of a strong sensation should lead to a release of endorphins. To wash it down, a heavy sticky drink that adheres to the mouth and tongue might also maximise flavour delivery. Or alternatively trying a variety of sodas with differing carbonation levels can provide intrigue and stimulation - many have an aggressive fizz that is highly compelling.”
Davis adds that sufferers should continue to explore spices and complexity of flavours once their taste returns. “Spices add complexity into the eating experience as their flavour perception finally returns,” he said.
Professor Spence agrees that food and drinks offering something more than just a flavour experience can potentially counteract smell and taste loss. “Crunchy, crispy, noisy and colourful food can make up for a loss of gustatory receptors and make things visually interesting because that's part of the flavour experience," he said.
He adds that the cases of anosmia and parosmia -- and the discombobulation of the COVID pandemic in general -- will continue to accelerate consumer demand for comfort foods, nostalgia brands and familiar items. "Everyone is feeling less certain and more socially isolated. It makes sense that in times of insecurity your customers are going to move away from new tastes, and they will continue to regress more towards comfort foods, familiar brands, and well-known things. Maybe those foods and drinks are offering something more than just a flavour: they’re offering emotional support.”