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From freshly baked pizza or popped popcorns in a cinema theatre to fresh sea breeze or wet paint at home, our nose can actually distinguish at least one trillion different odours.

It has been said for decades that humans are capable of discriminating between 10,000 different odours.

In the fresh study, scientists from Maryland-based Howard Hughes Medical Institute (HHMI) determined that our sense of smell is prepared to recognise this vast olfactory palette after testing individuals’ ability to recognise differences between complex odors mixed in the laboratory.

"Our analysis shows that the human capacity for discriminating smells is much larger than anyone anticipated," said HHMI investigator Leslie Vosshall who studies olfaction at the Rockefeller University.

"I hope our paper would overturn this terrible reputation that humans have for not being good smellers," she added.

Vosshall and Andreas Keller, a senior scientist in her lab at Rockefeller University, devised a strategy to present their research subjects with complex mixtures of different odours and then ask whether their subjects could tell them apart.

They used 128 different odorant molecules to concoct their mixtures. The collection included diverse molecules that individually might evoke grass, or citrus, or various chemicals.
But when combined into random mixtures of 10, 20, or 30, Vosshall says, they became largely unfamiliar. The scientists presented their volunteers with three vials of scents at a time: two matched, and one different.

Volunteers were asked to identify the one scent that was different from the others. Each volunteer made 264 such comparisons. Vosshall and her colleagues tallied how often their 26 subjects were able to correctly identify the correct outlier.

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 is like the way the census works: to count the number of people who live in the United States, you do not knock on every single door, you sample and then extrapolate," the researchers explained.

In this way, they estimated that the average person can discriminate between at least one trillion different odours.

Vosshall, however, doubts individuals are exposed to a trillion smells on a daily basis."But I like to think that it is incredibly useful to have that capacity, because the world is always changing," she added.

Plants are evolving new smells. Perfume companies are making new scents. You might move to some part of the world where you’ve never encountered the fruits and vegetables and flowers that grow there.

"But your nose is ready. With a sensory system that is that complex, we are fully ready for anything," Vosshall noted in the research published in the journal Science.