The human nose can distinguish at least 1 trillion different odours, a resolution orders of magnitude beyond the previous estimate of just 10,000 scents,
To investigate the limits of humans’ sense of smell, Andreas Keller, who is an olfactory researcher and co-author at the Rockefeller University in New York with his colleagues prepared scent varieties with 10, 20 or 30 elements selected from a collection of 128 odorous molecules. Then they pleaded with 26 study participants to specify the mixture that scented differently in a specimen set where two out of three scents were similar. When the two scents contained components that overlapped by more than about 51%, most participants struggled to discriminate between them. The writers then evaluated the number of possible mixtures that coincide by less than 51% to arrive at their estimate of how many smells a human nose can detect at least 1 trillion.