Sniff up ... humans can smell a trillion different odours!

HUMANS are not to be sniffed at when it comes to the sense of smell: a typical person can smell at least one trillion different odours according to the first scientific study to accurately estimate the olfactory power of the human nose.

It has been widely accepted for nearly a century that humans discriminate between no more than about 10,000 odours, but the latest findings show that the true number is much greater, conservatively estimated at one trillion.

This would make the human sense of smell more discriminatory than human colour vision, which can distinguish between 2.3 million and 7.5 million colour variations, or human hearing, which can discriminate between about 340,000 sound tones.

"The nose is really like a massive broadband technology that can take in huge amounts of information and pass it on to the brain. It is the only part of us that connects directly to the brain," said Professor Leslie Vosshall, of the Rockefeller University in New York.

"Our analysis shows that the human capacity for discriminating smells is much larger than anyone anticipated."

The latest study, published in the journal Science, involved the creation of unique combinations of smells derived from orange, anise and spearmint.

The volunteers were given three vials to smell, two of which were identical, and were asked to pick the odd one out.

Each of the 26 volunteers - 17 women and nine men - had to make 264 comparisons and, from these combined results, the scientists were able to make an extrapolation that gave them a conservative estimate of the overall olfactory power of the human nose.

Our sense of smell relies on two small odour-detecting patches in the upper nasal chamber each containing about five or six million receptor cells.