We see our human sense of smell as woefully inadequate compared to other animals – but awareness of our sense of smell has become more of a hot topic recently with the COVID-19 pandemic. A significant number of people who get the virus lose their sense of smell early on. It seems that a loss of smell can be a very good early sign of COVID-19 infection.

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Dr Karl:

G’day Dr Karl here,

Now love songs and poems have been written to the beauties of the lips, eyes and even the cheekbones of the human face. But for the poor old nose, the only options are to pay through it, or else keep it to the grindstone.

We see our human sense of smell as woefully inadequate compared to other animals – but that is totally incorrect. Even worse, the loss of smell can be quite disabling or even dangerous.

Awareness of our sense of smell has become more of a hot topic recently with the COVID-19 pandemic. A significant number of people who get the virus lose their sense of smell early on. It seems that a loss of smell can be a very good early sign of COVID-19 infection.

Our English language has relatively few words describing the quality of smell – words such as fragrant, stinky, and musty.

Lots of words describing smells basically just tell us where it came from – so something smells like a rose or a sweaty athlete - in the morning. Try to describe the smell of an orange – it’s close to impossible.

And then there’s a wide-spread myth that our human sense of smell is far inferior to that of other animals.

But it turns out that the number of neurons in the olfactory bulb in the brain is relatively constant across the animal kingdom. Olfactory just means related to smell, and the olfactory bulb helps to process the electrical signals involved with smell. One study looked at animals that ranged in body weight by a factor of about 5,000 (from a 15 g mouse to a 73 kg human). The number of neurons in the olfactory bulb varied by much less than 5,000 – it varied by a factor of only 28.

One study compared mice, spider monkeys and humans. As odours in the test, the scientists used six chemicals containing sulphur. And for three of those chemicals, we humans were thousands of times more sensitive than either mice or spider monkeys.

Another study looked at a chemical that helps give human blood its characteristic odour. We humans were just as good as dogs and rabbits at detecting blood - and a lot better than mice. If we humans were prepared to go around with our nose in the grass - either crawling or pushing ourselves along in a little wheeled trolley - we would be just as good as dogs and rabbits at following a trail containing human blood.

Not having a sense of smell can be very dangerous.

You cannot smell that rotten food is unsafe to eat, or that your house is full of gas, or that something on the stove is burning. In January 2021, a house in Texas caught alight. The whole family, except for a teenager, were infected with COVID-19 – and as a result, they had all lost their sense of smell. Luckily, the uninfected teenager did smell smoke, and woke everybody up so they all got out safely – a happy ending.

Losing your sense of smell nearly always significantly reduces your quality of life. You lose the pleasure of smelling the roses - and eating delicious foods. You lose that strange superpower of knowing what the neighbours are cooking, or if you can wear that shirt again.

So, next time I’ll immerse myself deeper into the loss of smell that happens in COVID-19.

Smell Part One

1. Dr Karl says that we say that our “sense of smell is woefully inadequate”. What does he mean by this?

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2. Explain what “keeping our nose to the grindstone,” means.

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3. What can losing your sense of smell be a sign of?

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4. What is a myth?

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5. What is the myth that Dr Karl wants to inform us about?

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6. What does olfactory mean?

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8. How does the human sense of smell compare with mice and spider monkeys?

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9. How do humans compare with other animals at detecting the odour of blood?

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10.Why was the Texas teenager able to save his family from a housefire?

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11. How does our sense of smell improve our quality of life?

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Writing – using the information from Dr Karl’s talk write between 300 – 500 words on Smell

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