Human Nose Can Sniff Out Over 1 Trillion Smells: Odors from Fragrant to Acidic

Ernest C. Crocker and Lloyd F. Harrison were two American chemists. In 1927 they published a paper noting that the human nose can tell the difference between four different odors (fragrant, acidic, caprylic, and burnt) allowing them to detect over 10,000 different scents.

Researchers at Rockefeller University deemed this number "pathetic" because it indicates that humans have a "comparatively low sense of smell." To refute this low number that hasn't been questioned in nearly a century, the researchers conducted hundreds of scent tests on 26 people.

Andreas Keller and his colleagues gave the research participants three jars, two of which contained the same smell, and their objective was to detect the lone scent. There were 128 different scents that the researchers mixed in groups of 10, 20, or 30, compiling 260 tests for the volunteers. To determine the nose's range of scent, they further examined the ingredients in each jar.

None of the subjects could tell the difference between jars that contained 90% of the same components, but the researchers discovered that most could distinguish scents that contained up to 57% of the same components. After the calculations were complete, Keller and Co. determined that the average person can tell the difference between 1.7 trillion smells.

But that is not the ceiling for what the nose is capable of smelling. "There are probably billions of odorous molecules and we only worked with 128 of them," said Keller in this National Geographic article. "Furthermore, we only mixed 30 components. There are many more mixtures with 40 or 50 components."

The findings of this study are astronomical, but they aren't too surprising. Our genes that enact our odorant receptors are the largest family in our genome. Humans have approximately 400 of these receptors, which have now been proved to dwarf our visibility of colors (a few million) and our identification of tones (about 340,000).

To read more about the Rockefeller University study, visit this Washington Post article.