The Human Nose Can Detect Over 1 Trillion Smells Say Scientists
Posted on March 20, 2014
Scientists say the human nose can detect over 1 trillion smells. By comparison, scientists say we can discriminate several million different colors and about half a million different tones. Previously, it was thought that the nose could detect only 10,000 different odors. The research was led by Andreas Keller of Rockefeller's Laboratory of Neurogenetics and Behavior. Keller is pictured above with some vials of odors from the experiment.
Leslie Vosshall, Robert Chemers Neustein Professor and head of the laboratory, says in a statement, "Everyone in the field had the general sense that this number was ludicrously small, but Andreas was the first to put the number to a real scientific test."
Keller ran an experiment where volunteers sniffed vials of odors that held different combinations of 128 odor molecules responsible for scents such as orange, anise and spearmint. Keller mixed the odor molecules in combinations of 10, 20 and 30 with different proportions of components in common. The volunteers received three vials. Two of the vials contained identical mixes. The volunteers were then asked to pick out the odd one.
Keller says, "Our trick is we use mixtures of odor molecules, and we use the percentage of overlap between two mixtures to measure the sensitivity of a person's sense of smell."
The results of the experiment show that the performance of the volunteers varied greatly. On average they could tell the difference between mixtures containing as much as 51 percent of the same components. Once the mixes shared more than half of their components, fewer volunteers could tell the difference between them. The researchers say this was true for mixes of 10, 20 and 30 odors. By analyzing the data, the researchers could calculate the total number of distinguishable mixtures.
Marcelo O. Magnasco, head of the Laboratory of Mathematical Physics at Rockefeller, and a collaborator in the experiment says, "It turns out that the resolution of the olfactory system is not extraordinary - you need to change a fair fraction of the components before the change can be reliably detected by more than 50 percent of the subjects,. However, because the number of combinations is quite literally astronomical, even after accounting for this limitation the total number of distinguishable odor combinations is quite large."
Keller says our ancestors probably had more use and more appreciation for our sense of smell than we do today. He also says 1 trillion may still be understating the number of smells a human nose can detect.
Keller says, "The message here is that we have more sensitivity in our sense of smell than for which we give ourselves credit. We just don't pay attention to it and don't use it in everyday life."
Some people are known as "super smellers." It would also be interesting to find out just how much odor sensitivity can vary among individuals.
The research was published here in the journal Science.