Update on our smelling prowess

Some time ago, I wrote about a study that said that we humans could smell 390 different smells. This seemed big enough to me but as commenter ChasCPeterson pointed out, this was not the full story because that number referred to the distinct number of olfactory sensors we have that can identify specific molecules but that we can actually smell combinations of these basic smells and the number of combinations can thus be much larger.

So how big is the range? It used to be thought, based on a very crude analysis done back in 1927, that we could distinguish between 10,000 smells. But Ed Yong writes that more recent studies suggest we can distinguish between more than a trillion smells!

Studying how well we can distinguish different smells is more difficult that studying how we distinguish between different colors or sounds. Yong describes the creative way that Andreas Keller of Rockefeller University set about it.

He gave volunteers three jars, two of which contained the same smell. Their job was to find the odd one out. The team made the smells from the same pool of 128 ingredients, which were mixed together in groups of 10, 20 or 30. They then paired these mixtures up so that some pairs had no ingredients in common, some were almost identical, and most were somewhere in between. Each volunteer sat through 260 of these discrimination tests.

After crunching the numbers, the team found that when the pairs of mixtures overlapped by less than 51 percent, most of the volunteers could tell the difference between them. And if they overlapped by less than 57 percent, most of them were distinguishable. This means that the average person can tell the difference between 1.7 trillion (that’s 1,700,000,000,000) different combinations of 30 ingredients.

But some people clearly have greater smell sensitivity than others and their range of smells goes up astronomically.

The 1.7 trillion figure is an average. At least one person in the study had an exquisitely sensitive nose that could potentially discriminate between more than 10 million trillion trillion combinations of 30 ingredients. Another volunteer could only make out around 70 million of them.

I would have been useless as a tester because my sense of smell is terrible. I doubt that I could get anywhere near even the lower figure.

But I wonder if being exceptionally sensitive to smells (and any other stimuli for that matter ) is not always a blessing but could be a curse except in specific situations. For example, having a good sense of smell could be professionally beneficial to a chef but could be a distraction to an ordinary diner.


  1. Enkidum says

    Note that there’s an enormous difference between discrimination and identification. That is, saying that two things are different does not entail the ability to say (or to perceive) what either one of them are.

  2. rq says

    Very interesting! Our Middle Child seems to have an extraordinary sense of smell. He can walk into a room and be disgusted (or delighted) by the smells in the air, and the rest of us barely sense anything at all. The rest of us are fairly ordinary.

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