Trillion-scented smorgasbord is everyday fare for our nose

OUR noses are sharper than they look. They can tell apart at least a trillion smells – far more than we thought. Every smell is a mixture of chemicals called odorants. The received wisdom was that the human nose can recognise about 10,000 different smells, but this was  a crude estimate that hadn’t been updated since 1927. To get a better idea, Andreas Keller and his colleagues at Rockefeller University in New York City concocted mixtures of 10, 20, or 30 chemicals drawn from a standard set of 128 diverse odorants. They had 26 untrained volunteers sniff 268 pairings of these mixtures, and they recorded how successful each volunteer was at distinguishing between the two. The more odorants shared by the mixtures in a pairing, the harder this was. Using statistical techniques to analyse the results, Keller calculated that people should be able to distinguish more than a trillion combinations of 30 odorants drawn from his set of 128. This is a conservative estimate because many smells involve  more than 30 odorants, and there are many more than 128 to draw from (Science, doi.org/r2d). The result suggests that people are surprisingly good at telling smells apart, even though most of us struggle to describe those smells in words. “We have an amazing olfactory capacity that has not been appreciated,” says Leslie Vosshall, who was part of Keller’s team.