Humans can detect one trillion smells: study

From here:

That’s some really good reporting. We can detect 1,000,000,000,000 smells instead of the previously estimated 999,000,000,000? Is “millions” the new word for “lots”?

Yeah, it stinks.

New product: Bertie Botts Scratch ‘n’ Sniff.

I’d like to know what this claim really means. Does it mean the human olfactory system can detect a trillion different molecules? Does it mean it can distinguish a trillion different molecules from each other? Does it mean it can detect a trillion different combinations of odor molecules?

My guess is that they enumerated the types of smell-sensing receptors we have, measured the top and bottom of their sensitivity range, and measured the smallest increment that could be resolved, and multiplied some stuff.

I feel so inadequate. Thre’s no way I can distinguish more than 998,500,000,000 smells at the absolute most, and even that is counting each of the many types of BO I’ve encountered on Metra trains as a different odor.

I just listened to NPR’s “Science Friday” where they were interviewing, at length, the guy who did this study, and that’s almost precisely how they did it. But insted of enumerating the types of smell-sensing receptors we have, they took 170 (or maybe it was 120 or something, I forget the exact number), and they had people actually smelling different combinations of them, and recording the smallest possible amount of change in each that the average person could still detect. Ends up that the smallest change for many odors is very very small, and so when you do the combinations, you end up with trillions of different odors.

The kicker is that they only used 170 known “pure” odors, when evidently science has established that the average human can detect 700 pure odors. So 1 trillion is the lower limit, and the actual limit is probably way too large to even consider.

But yeah, the “trillions of detectable odors” should really be called “trillions of detectable odor combinations.”

It was my understanding that there are still only a few hundred “pure” odors that the human nose can detect.
The scientist also said that this study shows that human noses are much more powerful than typically given credit. The reporter/interviewer asked about the comparison to dogs, and the scientist said that the dogs noses beat human noses in 2 important ways:

  1. If humans were sniffing along the ground all the time, that’s where the vast majority of the smells accumulate, and we’d get used to smelling a lot more things and learning more of distinguishing them.

  2. Dogs noses have a lot more nerve connections between the nasal passages and the brain, and this accounts for dogs being able to smell “better” than humans.
    In short, the take away from this study is that humans are actually really, really good at being able to distinguish between different smells, but other animals are still better at smelling most compounds at lower concentrations.

Also, it really is fair to call the combination of “pure” odors, odors themselves, because most people detect combinations of odors as completely new smells. They may be able to guess at “hints” or “notes” within the composite smell, but for most intents/purposes, combinations of smells are unique to the human nose. It’s not like you can smell something and say “oh that’s 30% pine, 40% gym sock, and 30% strawberry.”

I think it’s a lot like the number of colors that can be displayed by a 24 bit color graphics card. You must understand that one color is so very similar to another that it’s almost impossible to tell the difference between two colors that are similar to each other.