The Chemistry of Smell

The Chemistry of Smell

Did you know that humans can distinguish nearly 16 million different odors? How about that the patch of nerves that can sense odors in our nose is about the size of a stamp and is a yellow color? Even better, did you know that the smell of coffee can be described by the number 7683?

The chemistry of smelling is still being discovered and researched, but we have learned quite a few interesting things about smells and how humans, well, smell them. Scientists have come up with a way to number smells and even determine, based on the shape of a molecule, what something will likely smell like.




So, how does a smell even come about? In order to smell a smell, the substance needs to be volatile. That basically just means that it can evaporate in air and travel through air. That’s why you can’t really smell a rock, but you can smell alcohol. So, once a substance evaporates in the air, it may find its place in the air you breathe.

About 1-2% of each breath you take hits your olfactory cells. This is where the magic happens. That yellow stamp sized patch of cells I mentioned earlier is the group of cells known as your olfactory organ. The smelly substance will latch onto some of the olfactory cells and an electric signal will be sent up the cilia to your brain. At that point, you will finally smell something.

Here are some awesome and interesting facts about smells, smelling, and the chemistry behind smelling:

  • Vanillin, the compound that smells like vanilla, can be sensed by humans at a level of 0.0000000002 milligrams per liter of air!
  • We inhale about 1/10 of a liter of air per breath and of that only about 1-2% reaches our olfactory organ
  • Crocker and Henderson, two scientists, invented a system whereby smells could be categorized and labeled with a number. There are four categories in the system: flowery/fruity, acid/sharp, burnt/tarry, and caprylic/goatlike (very odd category, not sure what this smells like!). Each category gets a rating of 1-8. Coffee has a smell labeled 7683
  • Odors depend largely on their shape. In fact, two molecules can have completely different chemical makeups and still smell exactly the same
  • One molecule that fits into multiple olfactory receptors can have multiple smells
  • Molecules with a musky odor have a diameter of about 10 Angstroms and are shaped like a flat disk
  • Floral smelling molecules are shaped like a keyhole
  • Sometimes the charge of a molecule affects its smell. For example, pungent smelling molecules have a negative charge and putrid smelling molecules have a positive charge

Hope you found these tidbits about the chemistry of smell and how smell works as interesting as I did!

[Image credit] OakleyOriginals

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