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Our sense of smell is not to be sniffed at

March 2018

woman smelling tree blossom
We all smell things slightly differently

Even if you have never owned a dog, most people are aware of a dog’s amazing sense of smell. Greet a dog for the first time, and he will sniff all around you. Take a dog for a walk and he will spend half the time sniffing the ground.

Whereas for us poor humans, when we take a walk outside it is all about visual and verbal contact rather than smells and scents. This is because a dog has 220 million olfactory receptors (cell membranes responsible for the detection of odours). We humans only have around six million. Even a rabbit has ten times more smell capability than a human.

Our smelling capability is based around two small odour detecting patches high up in the nasal passages. They are made up of around five or six million yellowish cells.

What is interesting though is that each of our olfactory receptors is encoded by a different gene. This means they are not all the same.  Switzerland’s Boris Schilling, a leading biochemist, says that unless you are dealing with identical twins, no two persons will have the same genetic make-up for these receptors.

This means we may all smell slightly different things. Andreas Keller, a geneticist at Rockefeller University in New York City, says when he gives a talk, he tells everyone in the room that they will be smelling a different smell to everyone else. He also believes we all have inherited odorant blind spots, meaning some of us are unable to detect certain smells at all.

Interestingly scientific tests have shows that women constantly outperform men in smelling ability. Our sense of smell can diminish as we begin to age, especially once we reach the age of 70, possibly due to the loss of nerve endings and less mucus production in the nose. Mucus helps the odours to stay in the nose long enough to be detected by the nerve endings and it also helps to clear odours from the nerve endings, so a reduction in mucus can have a real effect.

Smoking can also affect a sense of smell, reducing sensitivity.

Smell can affect our bodies in surprising ways. Think about walking past a bakery and smelling that fabulous fresh bread. Our mouths can begin to water as the wonderful smell sends our salivary glands into overdrive. Professor Gordon Proctor, a specialist in salivary biology at King’s College, London, says smelling foods activates our olfactory receptors to send off a brain signal which notifies our salivary glands to work harder. He says saliva is a remarkable substance vital so that we can chew and swallow a meal, and smell can help the production of adequate volumes of this important fluid.

Smell of course is also vital for safety…smelling gas for instance immediately triggers our brain to danger and action.  Perhaps a clear indication of the power of smell is the emotion response that it can bring. Walk past perhaps some cut grass, and it can bring back memories and emotions when you were a child playing in a field; or smell a certain scent in a shop and suddenly you may conjure up images of perhaps your grandmother or a close friend who used that perfume.

Quite a few studies have been done to see if people can improve their sense of smell, and generally it seems that this can be achieved. French researchers Jane Plailly and Jean-Pierre Royet looked at professional perfumers and also students at the prestigious ISIPCA, a college in France that trains people working in the perfume industry. Plailly and Royet found that brains became more adept at recognising scents in the more experienced perfumers. Other research has shown that smell training, including repeated short term exposure to odours, can benefit people who have lost their sense of smell for various reasons.

In most tests a few basic types of odours are used, usually based on the scents identified 100 years ago by a German psychologist Hans Henning. He developed a classification of smells such as flowery, foul, fruity, spicy, burnt and resinous and modern tests are still based around some of these early findings. 

If you want to improve your sense of smell, a good way to start is to choose a few different scents from these areas, perhaps:
Flowery – rose
Fruity – lemon
Spicy – cloves
Resinous – eucalyptus.

Smell one for perhaps ten seconds, relaxing and inhaling naturally. Then move onto the next scent. It is suggested that if you do this twice a day, ideally in the morning and in the evening, then this could enhance your sense of smell. But of course, however much we train, we will never be near the wonderful abilities of man’s best friend!

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