Just like with sights and sounds, people are accosted with a multitude of smells like perfume, body odour and rotten egg.

What does your nose know? A lot more than you might expect.

Scientists studying the breadth of people’s sense of smell said the human nose can discern far more than the 10,000 different odours long cited as the outer limit of our olfactory abilities.

They concluded that the human nose can differentiate an almost-infinite number of smells – more than a trillion – based on their extrapolation of findings in laboratory experi-ments in which volunteers sniffed a large collection of odour mixtures.

“The single most important contribution of this research is that it revises this current idea that humans are terrible smellers,” said Leslie Vosshall, who heads the Laboratory of Neurogenetics and Behaviour at Rockefeller University in New York that conducted the study published in the journal Science.

This research revises this current idea that humans are terrible smellers

“We’re very good smellers,” Vosshall added.

Just like with sights and sounds, people are accosted with a multitude of smells like perfume, body odour, rose blossom, beer, rotten egg, paint, cut grass, spoiled milk, fresh popcorn, dog breath, ammonia, grilled meat, orange peel, pine, excrement, cinnamon, exhaust fumes, cookies and skunk spray.

Research has shown that people can distinguish several million different colours and about 340,000 audio tones, but the sense of smell had remained a mystery.

There has been a notion that people could discern only about 10,000 odours, but that was based on faulty assumptions, these researchers said.

Their experiments involved 26 men and women of various racial and ethnic groups, ages 20 to 48. The volunteers were given three glass vials of scents at a time – two identical to each other and the third different – and were asked to identify the different one.

The researchers used 128 different odour molecules with a wide spectrum of scents including ones smelling like citrus, mint, garlic, leather, tobacco and others, and then concocted mixtures for the volunteers. When combined into random mixtures of many odour molecules, the scents became largely unfamiliar.

“In general, I would say they had unfamiliar smells that were neither very pleasant nor very unpleasant. I thought ‘fresh garbage’ is a good descriptor,” said a researcher.

The researchers tallied how often volunteers correctly identified the odour that differed from the other two, then calculated how many scents an average person would be able to discern if given all possible mixes of the 128 odour molecules.

From this, they estimated that an average person can discern more than a trillion different odours. The researchers said even this number may be too low because many more odour molecules exist in the real world than the 128 used in the study – and they can be combined in innumerable ways.

The scents people encounter in everyday life usually are not a single odour molecule but rather a mix.