Odours evoke emotions
Strangely, many people find it difficult to name odours even when they are familiar. This may only be a fault of the English language, however, because speakers of other languages with a richer "smell" vocabulary can name smells equally as well as they can name colours. (www.sciencedaily.com)
On the other hand, we can experience waves of emotional memory when we get a sudden whiff of (say) the perfume our grandmother wore, or a childhood food, or in my case the smoke from a steam train. Australians overseas go mushy if they smell eucalyptus trees; and northern Europeans dream of Christmas when they smell pine trees. (theconversation.com)
Social implications of odours
Another peculiar thing about smells is that we stop noticing them if they are around all the time, even if they are objectionable. This was probably useful when people lived close proximity without ensuite bathrooms – or nowadays when you are camping. You may think your own clean home has no odour, yet you might notice a distinctive smell if you go to someone else's house – even if they are equally as clean – particularly if those people cook different foods from yours.
Mothers sometimes notice their children's odour only when it changes; maybe when the babies start eating new foods, or when they are sick. And, traditionally, some people have worn an item of clothing of an absent loved one, although they may not be aware it is the odour of the garment that reminds them of that person. (www.sciencedaily.com)
Our unique body odours (pleasant or otherwise) are produced both by natural hormones excreted through glands just under our skin, and also by the myriads of protective bacteria present in and on our bodies. In the past, this individual smell performed a very important social role in helping us know who was friend and who might be foe. (www.christiantoday.com.au)
Tronson du Coudray's art "Passion Scent"
Many animals make good use of their sense of smell
A lot of animals can distinguish many more smelly compounds than humans. If you were a dog, you would identify who had been in the room or yard, where they moved to, WHEN they were there, and for how long they had stayed; you would construct a four-dimensional smell-map of the family and visitors, even after they had all left!
There are many known examples of dogs being trained to indicate to their handlers when they smell contraband drugs, cadavers or survivors of an earthquake (and many other things). Sometimes, they can be used to detect diseases in humans because of the changed biochemistry in the body when someone is sick. Occasionally people can smell signs of disease too; the apple-like smell of diabetics being an extreme example. (www.medicalnewstoday.com)
Birds also use smell, although people once thought they didn't. Sea birds can smell a gas called dimethyl sulfide (DMS) from kilometres away, and they follow it to the Southern Ocean to feed on krill. This gas is released from phytoplankton as krill attack and eat it. The birds' droppings then help to fertilise that part of the ocean with iron. This cycle that may be important in regulating atmospheric carbon dioxide as well as also cloud formation. (news.ucdavis.edu)
Insects actually "smell" with their antennae. They use odour as well as colour to find their food, even if it we cannot smell anything. Mosquitoes, for instance, can detect the carbon dioxide on our breath!
But take heart, humans! We can, with practise, actually identify many more odours than previously thought; and that applies to all of us, not just the "super-smellers" who can detect such low concentrations of odorant molecules that most of us don't notice. (www.nature.com)
Chemistry, biology and physiology of smell (warning: science terminology).
There is a really simple and accurate diagram describing the way we sense odours at the following site: (www.exploratorium.edu)
If we are to smell something, then the smelly molecule must first waft on the air we breathe and come in contact with the mucous membrane inside our nose. There are sensory cells there, and on their surface are thousands of receptors.
Receptors are proteins that help the cell communicate with the world outside the cell and with other cells. Like all other proteins, they are coded for by our DNA. Due to their shape and other chemical properties, receptors only "dock" with complementary molecules, and this initiates a cascade of chemical or electrical signals in the body.
Tronson du Coudray's art "Scent of the Mist"
In our nose, there are also axons (the long filaments of nerve cells). As each odorant binds to the receptors, these nerves are stimulated in a complex pattern particular to each odorous molecule, and they send signals to a structure called the olfactory bulb, which is part of the brain situated conveniently close at the back of our nose. Here, the signals are partially sorted before being sent on to various parts of the brain for finer interpretation, which is what we sense as a smell. (www.mdpi.org)
Initially, chemists assumed the simple hypothesis that it was the shape of each chemical that determined which odorants "docked" with a receptor in a one-on-one arrangement. But they found several molecules with completely different structures with the same smell; and conversely, very similarly structured molecules with completely different odours. Biology is more complex than simple lab chemistry!
Linda Buck won the Nobel Prize along with Richard Axel in 2004 for sorting out the way each odorant interacts with receptors and neurons to form this biochemical "map", then how the signals get to the brain. She explains how her curiosity was initially piqued by someone else's paper in 1985: "How could nearly identical chemicals generate different odour perceptions? ... It was obvious to me that the first step to solving the puzzle was to determine how odorants are initially detected in the nose." At that time no-one knew there were olfactory receptors at all. She and colleagues spent ten intense years sorting out the puzzle, piece by little piece. (www.nobelprize.org)
Not the whole picture – YET
Another theory that has been advocated by a few chemists involves the interactions of the neurons with the vibrational energy generated as the electrons whizz around the odorant molecule. Even if partially true, this idea will not solve the entire puzzle, but it may be connected to 'brain waves' which help consolidate smell memories. (www.rsc.org, www.sciencedaily.com)
Mammals also have another smell detector, the veromonasal organ, which uses different nerves. This helps animals identify non-volatile compounds like hormones, and may be involved in "intuitive" behaviours. In humans, this may not be functional – but if it is, it could be why we unconsciously find some odours to be disgusting.
Next time you have a cold and your nose runs and therefore you can't tell if your feet smell, think about all the subtle ways in which our sense of smell enhances our lives!
1 Corinthians 12 verse 17 ESV "If the whole body were an eye, where would be the sense of hearing? If the whole body were an ear, where would be the sense of smell?"
Dr Mark Tronson is a Baptist minister (retired) who served as the Australian cricket team chaplain for 17 years (2000 ret) and established Life After Cricket in 2001. He was recognised by the Olympic Ministry Medal in 2009 presented by Carl Lewis Olympian of the Century. He mentors young writers and has written 24 books, and enjoys writing. He is married to Delma, with four adult children and grand-children.
Mark Tronson's archive of articles can be viewed at www.pressserviceinternational.org/mark-tronson.html