We know feet smell, but do your feet smell differently (hopefully better) than a friend’s? And if you can tell the difference between these four feet, can you do the same for all of your Facebook friends as well? According to a new study reported in the current edition of Science, the answer is a stinky yes and the total number of odorous feet and other smells humans can discern is over a trillion.

The research was proposed by Leslie Vosshall, the head the Laboratory of Neurogenetics and Behavior at Rockefeller University in New York, to challenge the long-accepted notion that the average human can only discern 10,000 distinct odors.

Trying to pick the matching smells

How did they come up with a trillion? Vosshall’s researchers gave 26 male and female volunteers three vials of scents and asked them to pick out the two that were identical. They used 264 different scents which were made from combining one or more of 128 different odor molecules from a wide range of smells. They computed how many scents could be created from all possible combinations of the 128 odor molecules, factored in how often the participants picked the matching smells and came up with the Sagan-like total of over a trillion.

The researchers admit this total is low because there are more odor molecules than the 128 they used in the test. Even ordinary smells are complex combinations of odor molecules which are detected by the 400 olfactory receptors in the nose and processed by the brain for identity as well as memory and emotional triggers.

Odor molecules

Vosshall hopes the study helps get our noses away from the grindstone and into the air.

Offices have no smells anymore. So I hope people will go outside and start smelling things.

What smell do you get when you mix random odor molecules? Andreas Keller, who led the study, described them this way:

In general, I would say they had unfamiliar smells that were neither very pleasant nor very unpleasant. I thought ‘fresh garbage’ is a good descriptor.

Excuse me while I go wash my feet.