Human Nose Can Discern at Least 1 Trillion Odors

A team of researchers, who rebelled against an arbitrarily set capability for our olfactory organ, used a so-far-untried statistical method to boost the number of different odors human nose can discern to at least a trillion.

After the assumption that human nose can distinguish between 10.000 odors remained unchallenged for decades, Leslie Vosshall and colleagues at the Howard Hughes Medical Institute (HHMI) had doubts about the reliability of the figure which crept into scientific literature and popular magazines in 1920s without any corroborating data.

“It didn’t make sense that humans should sense far fewer smells than colors.” In the human eye, Vosshall explains, three light receptors work together to see up to 10 million colors. “In contrast, the typical person’s nose has 400 olfactory receptors” she says.

In the experiment, findings of which were published in March 21, 2014 issue of Science, the team presented 26 volunteers with vials containing chosen samples from all possible mixtures prepared from 128 different odorants, with each sample containing two matched and one different scent. The subjects, asked to identify the scent different from others, made 264 such comparisons each.

Likening her method to a population census “when the officials do not go round knocking every door to count the inhabitants, but take a sample of a district and then extrapolate”, Vosshall said that’s how they arrived at the minimum trillion odors an average person could smell, “not, on a daily basis, of course.”  

Noting that the “world is constantly changing, with plants evolving new scents, for instance”, she said surely the number of odorants were not limited to 128 and therefore the actual capacity of the human nose could be far higher than the figure they had estimated.