Are there really good and bad smells?

Between good and bad smells, our nose is solicited all day long. But why do some smells bother us more than others?

We generally talk about pleasant fragrances that rekindle positive emotions. Flowery scents, spicy fragrances or gourmand perfumes help to titillate your senses and bring a positive sensory experience to you. But in our daily lives, many scents “do not smell of roses”, like the odor of fried food from a snack bar that disturbs your nostrils. After noise, bad smells take the second place on the podium of the worst nuisances. But are there good and bad smells and how do our nose and brain make a difference?

Your nose, that hero

We have already mentioned the power of olfactory memory, our strongest and oldest sensory perception. Thanks to a clever organization between the nose and the brain, we are able to store a considerable number of odors linked to memories, most of them positive. It is important to know that our nose is continuously solicited: we circulate about 12m3 of air on average per day, which is equivalent to more than 23,000 breaths for a human being. We are then exposed to a bunch of different scents! The sensors in our noses are therefore able to detect a very large number of smells every day. According to a study in the journal Science, humans could detect and analyze more than 1,000 billion different odors.

Good or bad smells: an innate sense…

We already know that there are no arguing about taste and colors! But is it the same for smells? How can some say they love the perfume of petrol while others hate it? Why does the perception of the same odor varies between two people with the same constitution? The explanation is above all a matter of science and genetic. Each person is “equipped” with about 400 olfactory receptors whose function is to activate neurons to send information to the brain. But several studies show that 30% of these receptors are different from one person to another. And each sensor can alter our perception of odors to radically change it. So, a scent can be delicious for someone and unbearable for another.

This is also why we do not detect odors with the same intensity. Our nose will evaluate a perfume according to its concentration. Some will be sensitive to a very low level of concentration while others will only start to smell at a much higher level of intensity.

…but a purely cultural interpretation

But whether a smell is perceived as pleasant or not, it is no longer genetics that comes into play but our personal interpretation. At first glance, there is no distinction, at least scientifically, between a good or a bad smell. The judgment we make is simply cultural!

At birth, a baby has no positive or negative appreciation. But as the child grows up, depending on education and learning, he learns that flowers and clean clothes smell good while excrement smells bad. Kids gradually build up their own analogies with referential smells. These references vary from one country to another and can be opposed according to cultures and traditions. In France, it is said that the more a cheese “smells” the better it will be. For Thai people, the smell of cheese is unbearable, but they delight in dishes made from fermented fish, which scent makes uninitiated Westerners shudder!

The interpretation of a scent is also partly due to the context in which it is smelled. Let’s continue with the cheese metaphor: if you like goat’s cheese, there are chances you like isovaleric acid, one of the dominant notes of this dish. This molecule is exactly the same as the one… in the feet perspiration (sorry for the picture if you were going to sit at the table). In this case, the molecule is perceived in a completely different way because the context is less positive.

Some smells that might surprise you!

Good or bad smells, how does our brain know the difference?

Be careful, after this paragraph you will not smell certain odors in the same way! Because there are scents that, depending on their concentration, can be as foul as they are pleasant. This is the case of civet or musk for instance, ingredients of animal origin, today produced thanks to synthesis. In their raw state, these raw materials have a very strong and not really pleasant smell that evokes fecal matter. But once diluted, they unveil a sensual and bewitching fragrance. Moreover, in excrement, we find several chemical components whose scent is far from being as disgusting as you might imagine, and which are used in many perfumes. Scatole and indole are naturally present in feces. However, in small doses, scatole evokes the smell of orange blossom and indole is used to synthetically reproduce the smell of jasmine!

To learn even more about these “off” notes, the perfumer David Moltz talks about them in an interview with the New York Magazine, to read here.

Some solvents, on the other hand, have a rather seductive smell. Acetone, ether, glue or even paint sprays can give off floral or fruity scents. But for once, do not let our noses guide us, and beware of these particularly toxic substances. That is also why some scents act on our brain like real drugs, with similar effects: faster heartbeat, olfactory hallucinations… But we will talk about that in a future article!

What are the smells that displease you the most?

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