Popular wisdom holds that good smells are in the nose of the sniffer. You like the scent of roses; I like fresh coffee. But a scientific study using a robotic "eNose" proves that pleasant smells are universal - and predictable.
Good smells are biologically hardwired
Using a device called an eNose, a group of Israeli neurobiologists were able to rank smells by pleasantness. They tested dozens of smells on people in Israel and Ethiopia (two very different cultural groups) in order to determine whether these good smells were universal or culturally specific. What they found was that many smells are universally rated as good or bad.
Write the authors of the new study:
We tuned an eNose to human odor pleasantness estimates. We then used the eNose to predict the pleasantness of novel odorants, and tested these predictions in naïve subjects who had not participated in the tuning procedure. We found that our apparatus generated odorant pleasantness ratings with above 80% similarity to average human ratings, and with above 90% accuracy at discriminating between categorically pleasant or unpleasant odorants. Similar results were obtained in two cultures, native Israeli and native Ethiopian, without retuning of the apparatus. These findings suggest that unlike in vision and audition, in olfaction there is a systematic predictable link between stimulus structure and stimulus pleasantness. This goes in contrast to the popular notion that odorant pleasantness is completely subjective, and may provide a new method for odor screening and environmental monitoring, as well as a critical building block for digital transmission of smell.
They add:
We could predict whether a person who we never tested before would like the odorant, and this prediction was consistent across Israeli and Ethiopian cultural backgrounds. We argue that this difference was not a reflection of better hardware (in fact, an eNose is less precise than a modern camera or sound recorder), or better algorithms, but rather a reflection of a fundamental biological property of the sense of smell.
This has implications for perfumers and other entrepreneurs who want to sell things that smell good across the globe. But for the rest of us? It provides a definitive list of the best and worst smells.
The best and worst smells
According to the humans tested, what were the best smells? From the range of essential oils that were tested, these were the winners.
1. lime (fruit)
2. grapefruit (fruit)
3. bergamot (similar to an orange in scent)
4. orange (fruit)
5. peppermint
Here are the runners-up:
6. freesia (flower)
7. amyl acetate (a molecule that smells like apples and bananas)
8. cassia (similar to cinnamon)
9. mimosa (flowering tree)
10. fir (tree)
And the worst? The researchers say the smells consistently ranked the worst included "either carboxylic acids or amines [and] cyclohexanol." These would probably produce sharp, vinegary smells. Among the lowest-ranked of the so-called "pleasant" smells were musk and patchouli.