Human Nose Can Distinguish More Than 1 Trillion Scents
March 21, 2014

Humans Capable Of Detecting Over One Trillion Different Smells

redOrbit Staff & Wire Reports - Your Universe Online

For decades, experts have claimed that people were capable of detecting 10,000 different odors, but new research appearing in the March 21 edition of Science suggests that the actual number of scents detectable by the human nose is considerably higher.

In fact, according to an experiment led by Andreas Keller of the Rockefeller University Laboratory of Neurogenetics and Behavior, human noses and brains are sensitive enough to allow men and women to sense at least one trillion different odor combinations, the university said in a statement Thursday.

Professor Leslie Vosshall, head of the laboratory and one of the study authors, explained that most researchers were aware that the 10,000 figure was “ludicrously small,” largely because the number is so much smaller than the amount of colors that are detectable by light receptors in the human eye (10 million colors).

However, she said that Keller’s team was “the first to put the number to a real scientific test” and demonstrate that “the human capacity for discriminating smells is much larger than anyone anticipated.” The study authors added that their findings indicate the olfactory receptors far outperform the other human senses in the sheer amount of physically different stimuli they are capable of discerning.

Keller, Vosshall and their fellow investigators used 128 different odor molecules responsible for scents such as orange, anise and spearmint. They then combined those molecules in sets of 10, 20 or 30 with different proportions, and recruited 26 volunteers to distinguish between each mixture. The subjects each received three vials, two of which contained identical component combinations, and were then asked to pick out the unique one.

The researchers found that, while the ability of individual volunteers to successfully complete the task varied greatly, those men and women could on average distinguish between mixtures containing as much as 51 percent of the same components. One the mixes had more than half of their components in common, however, fewer volunteers could tell the difference – a phenomenon which proved true for mixes of 10, 20 and 30 different scents.

By analyzing their data, Keller’s team was able to calculate the total number of mixtures that the volunteers could distinguish between. Based on their calculations, they determined that people are capable of discerning between at least one trillion olfactory stimuli – likely far more, since there are more than 128 base odorants they worked with.

“I think we were all surprised at how ridiculously high even the most conservative lower estimate is. But in fact, there are many more than 128 odorants, and so the actual number will be much, much bigger,” Vosshall said.

“The resolution of the olfactory system is not extraordinary – you need to change a fair fraction of the components before the change can be reliably detected by more than 50 percent of the subjects,” added colleague Marcelo O. Magnasco, head of Rockefeller’s Laboratory of Mathematical Physics. “However, because the number of combinations is quite literally astronomical, even after accounting for this limitation the total number of distinguishable odor combinations is quite large.”

Image 2 (below): Vials of odors are among hundreds that Rockefeller University researchers used to measure volunteers' ability to distinguish between scents. Credit: Zach Veilleux / The Rockefeller University