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Smell: the secret world of our most underrated sense

ABC News logo ABC News 21/09/2016 Dean Blake, Catalyst

If you had to choose between your sense of smell or your access to technology, which would you choose?

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In a survey of young adults, just over half said they would rather lose their sense of smell than their access to technology, like laptops or smartphones. 

While a modern life without a mobile phone or social media would be especially difficult, anosmia — the loss of the ability to perceive odours — can impact a person's life far more than one might expect.

Suffice to say that our sense of smell is underrated; perhaps because unlike our other senses, much of our sense of smell is subconscious.

How does our sense of smell work?

Essentially, smelling is our ability to detect chemical signals. These signals enter our nose, are sampled by around 5 million receptor cells, and are translated for our brain to understand.

These cells allow us to distinguish between around 1 trillion different scents, making our sense of smell far more acute than our vision or hearing, which lets us see several million colours and hear about 500,000 tones.

Why then do we tend to rely more on our vision and hearing in our daily lives, and react to odours only if they are particularly strong — be they pleasant or otherwise? Humans have done a pretty good job of creating visual and auditory stimuli – television, painting and music for example.

However, it is difficult to translate a 'smell' through any of these mediums.

Even if you could, it would be far more problematic to send a particular message or thought by smell than it would be through visual or auditory means, which has led to far more emphasis being placed on our sight and sound as conveyors of information in our society.

So then, how do we use our sense of smell — even when we don't realise it?


It is well known that animals are able to communicate through smell — most notably, dogs — but it's surprising to learn that humans may do this as well, albeit subconsciously.

A 2015 study by the Weizmann Institute found that participants, being filmed via hidden cameras, smelled their hands twice as often after having shaken hands with a researcher.

This behaviour suggests that humans may use bodily scents to gather information about those around them.

In fact, as a 2014 paper published by the Association for Psychological Science found, humans are able to understand the emotional state of another person based purely on their scent.

The paper, tiled 'A Sniff of Happiness', found that women who smelled sweat produced during periods of happiness, fear and neutral feelings were able to identify the emotional state of the person who produced the sweat.

"Indeed, exposure to sweat from happy senders elicited a happier facial expression than did sweat from fearful or neutral senders", the researchers said.

"Humans are a social species with the capacity to share these positive effects, using not only modalities such as vision, hearing, and touch, but also — as this exploratory study indicates — the sense of smell."


Our sense of smell is the only sense which is directly linked to the parts of our brain which regulate emotion, learning and memory — specifically the Hippocampus and the Amygdala.

This can explain why certain smells have the capacity to send us 'back in time', strongly evoking memories and emotions we may not have thought about for years.

Dr Paul Moore of Bowling Green State University believes this is as a result of odours laying down 'odour memories' which are stored with emotions in our memory.

Later in life, when we smell a familiar scent, the emotions and memories tied to it in our brains are also brought back up. This is may be why we can get nostalgic when smelling a scent from our childhood, or the perfume of a former lover.


However, our sense of smell also serves a far more practical purpose — that of warning us of danger.

Whether it is the scent of smoke from a fire, a gas leak or the smell of putrid food, we rely on smell to help us avoid dangerous situations.

It is known that women have a stronger sense of smell than their male counterparts, but pregnant women seem to have this sense enhanced ever further; perhaps as a method of protecting themselves from eating harmful food, or detecting unsafe situations, in order to preserve their — and their child's — life.

Some scents, however, are far too minute to be detected by the human nose.

Dogs, which have a far stronger sense of smell than humans, can be trained to detect cancerous cells in test tubes — and have alerted owners to their own, undiagnosed cancer after this training.

Researchers at CSIRO have taken this concept and created the 'Cyber Nose' — a machine capable of detecting minute changes in the chemicals of a patient's breath in order to aid in early detection of diseases such as malaria.

CSIRO senior principal research scientist Steven Trowell believes, given time, the Cyber Nose could be extended to detect cancerous cells, and will be able to be used in poor communities as well as in GP surgeries in order to dramatically reduce the cost, and increase the efficiency, in early diagnosis of several life threatening diseases.

This concept could be used to improve security against biohazards, such as being used at airports to detect dangerous chemicals, illegal plants or explosives.

A life without smell

Even if we don't notice it, our sense of smell plays a significant part of our daily lives — so what happens when it is taken away?

Much of our sense of taste comes from the odours emitted by our food, and while sufferers of Anosmia may retain the ability to experience the five main food flavours: salty, sweet, sour, bitter, and umami (a Japanese word meaning a pleasant, savoury taste) they are unlikely to experience "about 95 per cent of the flavour of food".

When you are only left with 5 per cent of a food's flavour, much of its appeal can be stripped away. Anna Barnes, a sufferer of anosmia, struggled to eat for months after losing her sense of smell.

As a result she no longer enjoyed eating fruit, as without flavour many fruits become slimy and bland. However, she retained her love of vegetables due to them having a far nicer texture.

The absence of smell also opens the opportunity to make simple mistakes many of us avoid without even noticing.

"I had some early mix-ups: accidently drinking vodka thinking it was water," Ms Barnes told Catalyst. "You eat a lot of off food without realising — I've vomited from having off milk many times."

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