60-Second Science

Human Nose Tallies More Than a Trillion Scents

Based on humans' ability to discriminate between various close odors, researchers calculate that the average person can distinguish at least a trillion smells. Cynthia Graber reports


A bloodhound’s sense of smell is far better than its owner’s. But human olfaction is still nothing to sneeze at. Because your nose can detect at least a trillion individual scents. That’s according to research in the journal Science. [C. Bushdid et al, Humans Can Discriminate More than One Trillion Olfactory Stimuli]

Researchers mixed together combinations of some of 128 different odors. Study subjects then smelled three samples: two of the combination scents that were the same and one that was different. Based on subjects’ id’s of the different smells, the researchers gauged how close the mixtures could be and still be distinguishable.

Those findings let them determine how many different scents could exist made of combinations of the original 128 odors. The result was more than a trillion.

Researcher Andreas Keller of The Rockefeller University told the journal Science’s podcast why humans have such a discerning sense of smell:

“Our olfactory system evolved…to discriminate very similar smells, like my baby from my neighbor’s baby, milk that’s still good from milk that turned bad. So those are very similar smells that only differ in a few components. So we evolved to be able to make those discriminations. And as a side effect of that we can discriminate all those other odors, too.”

—Cynthia Graber

[The above text is a transcript of this podcast.]

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