The sense of smell has been heralded as the greatest portal into the past, better at drumming up nostalgia than both audition and sight. Yet for the universal benefits conferred by smell, a new study argues the sense remains unique for all of us, and that, precisely like fingerprints, no two people smell the same.

This isn’t to say people don’t smell the same — surely a team of chefs or football players carries the same scent as their cohorts after a long day — but rather that a single amino acid encoded on one gene can mean one person finds a certain smell pleasant while someone else can find it utterly repulsive. Researchers at Duke University suggest the finding opens up olfactory to nearly a million variations of the 400 genes coding for the receptors in our noses, making the world of smell truly boundless.

"There are many cases when you say you like the way something smells and other people don't. That's very common," Hiroaki Matsunami, associate professor of molecular genetics and microbiology at the Duke University School of Medicine, said in a news release. "We found that individuals can be very different at the receptor levels, meaning that when we smell something, the receptors that are activated can be very different (from one person to the next) depending on your genome."

While the human genome for olfaction has been identified at great length already, researchers have remained unsure what exactly turns on the receptors. Matsunami and his team decided to clone 500 receptors each from 20 people whose amino acids only differed by one or two degrees, and proceeded to expose the subjects to odor molecules that would excite the receptors. The difference in excitement would alert the experimenters to known odorant-active receptors.

Through exposure to varying amounts of certain odors, such as vanillin and guaiacol, the team discovered twice the receptors that had previously been known to activate in individuals, bringing the current total to 40. Matsunami found that two given strangers would conservatively share 30 percent of odorant receptors with each other. Overall, he and his colleagues believe the findings may prove useful for marketers who wish to better target people according to the smells they personally find pleasant.

"These manufacturers all want to know a rational way to produce new chemicals of interest, whether it's a new perfume or new-flavored ingredient, and right now there's no scientific basis for doing that," he said. "To do that, we need to know which receptors are being activated by certain chemicals and the consequences of those activations in terms of how we feel and smell."

Matsunami’s research adds a robust background for prior research into smells, such as a study conducted earlier this year that found humans are capable of discerning only 10 different smells. These include: fragrant, woody, non-citrus fruity, sharp/pungent, chemical, minty/peppermint, sweet, popcorn, sickening, and lemon. While the researchers at Bates College and University of Pittsburgh concede that natural smells likely include a combination of these 10, they argue the human nose is sensitive enough only to pick up a finite amount.

This complicates the findings of Matsunami’s team, which argues our DNA predicts how we’ll interpret a smell. What emerges is a fundamental question of perception, namely, even if our sense of olfaction detects a smell in a way that’s unique to our DNA, our tools of classification (i.e. language) prohibit us from vocalizing that abstract difference. So, we make one of 10 comparisons.

One “possibility is that early olfactory processing only resolves odor quality to a degree sufficient to rank relative pleasantness,” the team states in its report, “with further parsing of this percept into discrete categories occurring through mechanisms involving learning and context.”

 

Source: Mainland J, Keller A, Li Y. The missense of smell: functional variability in the human odorant receptor repertoire. Nature. 2013.