The scent of lily of the valley cannot be easily bottled. For decades companies that make soap, lotions and perfumes have relied on a chemical called bourgeonal to imbue their products with the sweet smell of the little white flowers. A tiny drop can be extraordinarily intense.
If you can smell it at all, that is. For a small percentage of people, it fails to register as anything.
Similarly, the earthy compound 2-ethylfenchol, present in beets, is so powerful for some people that a small chunk of the root vegetable smells like a heap of dirt. For others, that same compound is as undetectable as the scent of bottled water.
These — and dozens of other differences in scent perception — are detailed in a new study, published this week in the journal PNAS. The work provides new evidence of how extraordinarily different one person’s “smellscape” may be from another’s. It’s not that some people are generally better smellers, like someone else may have better eyesight, it’s that any one person might experience certain scents more intensely than their peers.
“We’re all smelling things a little bit differently,” said Steven Munger, director of The Center for Smell and Taste at the University of Florida, who was not involved in the study.
The scientists who conducted the study looked for patterns in subjects’ genetic code that could explain these olfactory differences. They were surprised to find that a single genetic mutation was linked to differences in perception of the lily of the valley scent, beet’s earthiness, the intensity of whisky’s smokiness along with dozens of other scents.
“I think it’s a very important finding,” said Stavros Lomvardas, a neuroscientist at Columbia University’s Zuckerman Institute, who was not involved in the research either.
The study was conducted in a large room at Rockefeller University in New York City. Around 300 subjects were invited to sit in front of a computer screen surrounded by 150 jars of assorted odours. The screen alerted them to which jar sniff at any given time, and they then rated the intensity of each on a scale from 1 (extremely weak) to 7 (extremely strong) and pleasantness from 1 (extremely unpleasant) to 7 (extremely pleasant).
Before leaving, participants provided a blood sample.
“We sequence their DNA and look for small differences between people,” said Casey Trimmer, a geneticist and the lead author of the study. (At the time, she was affiliated with the Monell Chemical Senses Center. She now works for Firmenich, a flavour and fragrance company.)
The idea that people experience certain scents differently is not new. Scientists have known for a while that for some people cilantro tastes like soap and beets taste like dirt for reasons likely connected to smell. They’ve also known that only some people can detect the chemical that makes urine smell differently after someone has eaten asparagus, and that the scent of a compound in men’s sweat is different depending on one’s genetic code.
“Some people find androsterone very disgusting and intense and sweaty (me included),” wrote Leslie B Vosshall a neuroscientist at The Rockefeller University, who identified the genetic code behind the sweaty difference in 2007. “Others find it not too unpleasant and use adjectives like ‘chemical’ or ‘vanilla,’ yet others cannot smell it at all.”
What’s different about this study is that it attempted to identify the genetic underpinnings of a broader number of scent-detection differences. You have around 400 olfactory receptors at the top of your nasal cavity and they activate differently depending on what you’re smelling. “Odours bind and turn on specific detectors, and this pattern of activation tells us if we’re smelling a flower, how strong we find it, whether we like it,” said Trimmer. “Small changes in the gene for the receptor can change its shape and how well the odour fits, thereby altering perception of the odour.”
As they looked for patterns in the genetic sequences and compared them to how the participants rated the scents, the scientists thought that androsterone would be an outlier in that differences can be traced to a single receptor. “But here we show that this phenomenon is not uncommon,” she said.
How it matters — beyond giving people a biology-based excuse to refuse to eat beets and buy overpriced whisky — is that it helps demystify the olfactory system a bit further.
“Olfaction is the most important sense for the rest of the animal kingdom,” said Lomvardas. And though its essential role is less obvious when humans don’t have to sniff out their next meal, it still affects much more than just perfume preference and flavour experience. There is evidence that reduced sense of smell has psychological consequences, he said, and it may offer early clues of an oncoming neurodegenerative disorder such as Alzheimer’s disease.
Of course, genes are not the only determinant of scent. Rachel Herz, who studies the psychological science of smell at Brown University calls this new study “great and important” but points out that there are many other factors at play, including attention, past associations and expectations.
“There’s also an ability to create odour illusions and flip people’s perception of an odour,” she said. She’s done this by presenting people with a chemical combination and telling them that it’s vomit. She then presented the same chemical combination and told them it was Parmesan cheese. The participants refused to believe that the samples were the same, she said, as one was so clearly disgusting and the other was so clearly delicious.
© 2019 The New York Times