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The Human Nose Could Detect At Least One Trillion Odors

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The human nose is capable of discriminating at least one trillion different odors, according to a recent study The Nation reported.

Researchers from the Howard Hughes Medical Institute determined that human's sense of smell can recognize differences between complex odors mixed in the laboratory. For decades it was believed that humans could detect only 10,000 scents, putting the sense of smell well below the capabilities of sight and hearing, The Nation reported.

"Our analysis shows that the human capacity for discriminating smells is much larger than anyone anticipated," study co-author Leslie Vosshall, head of Rockefeller University's Laboratory of Neurogenetics and Behavior, said in a statement.

For the study, scientists subjected 26 participants to mixtures made with 128 different odorant "molecules that individually might evoke grass, citrus or various chemicals, but were combined in groupings of up to 30," The Nation reported. Volunteers sampled three vials at a time -  two that were the same and one that was different - to see if they could detect which was the outlier.

"We didn't want them to be explicitly recognizable, so most of our mixtures were pretty nasty and weird," Vosshall said. "We wanted people to pay attention to 'here's this really complex thing - can I pick another complex thing as being different?'"

Volunteers were able to on average discern the difference between vials with up to 51 percent of the same components, with fewer volunteers detecting a difference once the mixtures shared more components.

From there, they extrapolated how many different scents the average person would be able to discriminate if they were presented with all the possible mixtures that could be made from their 128 odorants.

 "It's like the way the census works: to count the number of people who live in the United States, you don't knock on every single door, you sample and then extrapolate," Vosshall said. "That's how I like to think of this study. We knocked on a few doors."

The previous estimate for the nose's capabilities dated to the 1920s and was not backed by any data, The Nation reported.

"Objectively, everybody should have known that that 10,000 number had to be wrong," Vosshall said.

She explained that it didn't make sense that humans should sense far fewer smells than colors. In the human eye, Vosshall explains, three light receptors work together to see up to 10 million colors. In contrast, the typical person's nose has 400 olfactory receptors.

"We know exactly the range of sound frequencies that people can hear, not because someone made it up, but because it was tested. We didn't just make up the fact that humans can't see infrared or ultraviolet light. Somebody took the time to test it," Vosshall said. "For smell, nobody ever took the time to test."

The findings were published in the journal Science.

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