How well do you understand your sense of smell? Try these three experiments

Scientists and philosophers have traditionally been quite snooty about the sense of smell. Charles Darwin believed smell to be "of extremely slight service" to humans, and Immanuel Kant regarded it as "most dispensable" of the senses.

It's doubtful that sufferers of long Covid would agree. Anosmia, or loss of smell, has been one of the most persistent symptoms of coronavirus – and, in a strange way, the pandemic has highlighted the value of what AS Barwich calls "the Cinderella of the senses".

Barwich is the author of Smellosophy: What the Nose Tells the Mind, a beguiling analysis of olfactory experience that is fast becoming a core reference work in the field. The sort of statements like those above from Darwin and Kant are dismissed by her as "throat-clearing" generalisations not based on fact. She tells her students to "just scratch them" from their minds.

Smell alerts us to stinks that may accompany danger. It allows us to enjoy flavour in our food (see below). But that’s only the start of it. Smell, according to Barwich, is “an extended touch perception” that connects us to the wider world. Moreover, she argues, studying the sense of smell could be key to understanding the nature of consciousness – something that remains one of the great mysteries of science.

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The AS stands for Ann-Sophie. She publishes under the initials to combat gender bias or, to be more precise, the double bias that faces a woman in a field of study that some dismiss as a feminine concern.

“If you Google ‘smell’ the first pictures you’ll see are women smelling a rose, and I think, For heaven’s sake, I’m so bored of this image,” she tells The Irish Times.

Of the use of initials, she says: “I thought of JK Rowling, who did it for the same reason … and I noticed there is, of course, gender bias when it comes to the senses. I wanted people to take smell seriously and look at the fact that this is hardcore molecular biology. Yes, there is also perfumery – which is also hardcore molecular biology – but there is chemistry and psychology that people are not always recognising [in the study of smell], and it’s easy to dismiss.

“For a woman writing about that, I just needed to avoid the bias that allowed people to avoid taking this seriously.”

Just why is smell so neglected within the study of senses?

“I would say three reasons. One is people thought it was unimportant – turns out, with Covid, it’s not,” Barwich replies. “The second is it’s very hard to study. The third is it does work differently from the other senses or, perhaps it’s better to say, we’ve realised through smell that our senses do not work the way we think they work.”

The science is remarkably young. It was only in 1991 that Linda Buck and Richard Axel discovered the olfactory receptor genes responsible for smelling. It won them a Nobel prize.

If you move from, say, Ireland to South Africa, Brazil… or Germany you will perceive new chemicals because there are new food stuffs, new plants

“Smell has often been neglected because people thought it’s purely subjective,” says Barwich, but different perceptions of the same scent can be accounted for by biological variations. You have hundreds of receptors in your nose – millions if you count the smaller type (“I think the official term is ‘s**t tons’ of receptors,” says Barwich) – and “what is pretty cool is you and I don’t have the same receptors expressed”.

“Even in the course of our own lives, the receptors constantly regenerate every three to four weeks – otherwise after a few colds you would lose the ability to smell. That means you have a system that can adapt to its chemical surroundings.

“If you move from, say, Ireland to South Africa, Brazil … or Germany you will perceive new chemicals because there are new food stuffs, new plants … So, even if it looks subjective, the objectivity is the general process by which your biology responds to the environment.”

The implications of such discoveries are far-reaching – and this is where Barwich’s interest in philosophy comes in. She makes a convincing case that the western world has an unhealthy fixation with vision. We tend to think of the senses as a hierarchy with sight at the top – and, what’s more, we generally overlook the many other senses beyond the “big five”.

Scientists and philosophers are only now beginning to take seriously senses such as proprioception – your body’s ability to sense its location relative to other moving objects. Or interoception – your sense of what’s going on inside your body, an understanding of which can help, for example, to explain how hunger affects judgment.

“Neuroscience prompts us to rethink our basic philosophical categories,” says Barwich. “Some people say you do philosophy as a handmaiden to science. I think this is a misunderstanding. What philosophy can do is much more constructive and work in collaboration with scientists by developing questions: What questions arise from these developments?”

The Covid-19 pandemic has given an added impetus to this research.

I heard a conversation with a nurse interviewing people who had lost their sense of smell and one of them said it felt like she was cut off from the world

Initially, she says, “doctors were saying, ‘Loss of smell is just loss of quality of life.’ I was saying, ‘What? Quality of life is a key part of life.’

“I heard a conversation with a nurse interviewing people who had lost their sense of smell, and one of them said it felt like she was cut off from the world, behind a wall of glass. She couldn’t connect to the world the same way.

“That was striking to me, because the way we smell is almost like touching the invisible world. If you go to a new place you get a sense, a feeling for it … Your nose interacts with the molecules in the air.

“That’s good if you go into a field with nice smells; it’s also bad if you go into a public toilet … because the smell – the s**tty molecules – actually hit your nose. Smell gives you direct material contact with the world – and this contact was missing with Covid.” Those affected “realised how isolating it can be by losing a sense of smell”.

These is a lesson here for all of us: Your nose is not to be sniffed at. Or, as Barwich puts it, smell is something “that cannot be replaced”.

How well do you know your senses? Three experiments

You’ve probably tried the experiment of eating a piece of food with your nose pinched – it becomes less flavoursome or the taste disappears altogether.

But here’s another test: Put your finger on your upper lip and swallow. You should feel a small blast of air coming through your nostrils. That’s warm air being pumped from your lungs – and it allows food molecules which are broken down from chewing to travel up to receptors in the nose.

But that’s only a small part of the story of how your senses interact. Vision plays a further role, as can be shown by the “parmesan-vomit experiment” – something else you can try at home.

Find something that smells putrid (researchers used a mixture of acids) that can be placed in two different jars, one labelled "Parmesan" and the other "vomit". Though the smell is the same in each jar, people typically experience the "olfactory illusion" of sensing one scent as different to the other. "Context matters to the categorisation of odour," Barwich explains.

Or, as any chef will tell you: presentation makes all the difference.