Smell Test: Humans Can Detect 1 Trillion Scents, Study Says

Scientists had previously believed humans could detect only about 10,000 smells.

Researcher Andreas Keller sits in his lab, surrounded by vials of odors he and his colleagues used to measure volunteers' ability to distinguish between scents.

Researcher Andreas Keller sits in his lab, surrounded by vials of odors he and his colleagues used to measure volunteers' ability to distinguish between scents.

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The nose knows.

The human sense of smell can detect more than 1 trillion different scents, a new study claims – far more than the previously accepted number of 10,000 odors.

"Everyone in the field had the general sense that this number was ludicrously small,” Leslie Vosshall, professor and head of The Rockefeller University's Laboratory of Neurogenetics and Behavior, said of the 10,000-smell figure. “But Andreas was the first to put the number to a real scientific test."

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Andreas Keller, who ran the so-called “Smell Study” at the Rockefeller lab, had volunteers smell different scent mixtures, each made up of combinations of odor molecules responsible for smells such as spearmint, orange and anise. Each volunteer received three vials, two of which held identical mixtures, and then had to pick the one that was different.

“Our trick is we use mixtures of odor molecules, and we use the percentage of overlap between the two mixtures to measure the sensitivity of a person’s sense of smell,” Keller said in a statement.

On average, volunteers not only could tell the difference between the mixtures, but they could even do so when as much as 51 percent of a scent was comprised of the same components. After the 51 percent mark, fewer subjects were able to distinguish between smell mixtures.

Even with this limit, though, “the number of combinations is quite literally astronomical,” said Marcelo O. Magnasco, who collaborated on the study and is head of the Laboratory of Mathematical Physics at Rockefeller.

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Keller speculated that humans might once have had far better appreciation for their sense of smell than we do today, thanks in part to modern touches like showers and refrigerators.

“We have more sensitivity in our sense of smell than for which we give ourselves credit,” Keller said. “We just don't pay attention to it and don't use it in everyday life.”

The findings were published this week in the journal Science.