Science and Tech


Humans Can Distinguish Over 1 Trillion Smells, Says Study

A new study from The Rockefeller University shows humans can distinguish between 1 trillion different smells, far more than previously thought.
Posted at 9:57 PM, Mar 20, 2014

Our eyes can distinguish at least 2 million different colors, and our ears can catch about 340,000 different tones. But new research shows that our nose might have all of our other senses beat — it can pick up more than 1 trillion different odors.

Scientists at The Rockefeller University tested the proboscis — that's the nose of a mammal — by creating scent mixtures of 128 different smell molecules. The researchers asked people to pick between three smells: two of the same scent, and one slightly different scent.

The study found more than half of the participants could find the odd smell out as long as the mixture was at least 50 percent different. The scientists then extrapolated from their own data to find all the possible smell combinations a nose can distinguish, and arrived at more than 1 trillion different scents.

​Study lead Andreas Keller told Science"It's not that we need to smell all those odors, but what happened is that our olfactory system evolved to have a very good resolution to discriminate very similar smells.

The study is giving the nose some long overdue credit — The Washington Post notes previous estimates capped the number of smells we can distinguish at 10,000 for decades.

"The 10,000-smell estimate stems from an outdated 1927 manuscript by two American chemists. They came up with an odor classification system based on four primary smells ... with a total of 6,561 possible different smells. Later, that number was rounded up to 10,000."

And a smell scientist told HealthDay, since the study limited itself to 128 basic components, 1 trillion smells might be just the beginning of what our noses can accomplish.

"If you were to do a test involving all kinds of intensities and many more components, you'd arrive at a figure that is probably much, much higher than a trillion. ... I'd say that a trillion is probably a severe underestimate of our ability to smell."

The study was published Thursday in the journal Science.