How many types of smells can the human nose distinguish?


A human nose has around 400 types of scent receptors. When the smell of coffee wafts through a room, for example, specific receptors in the nose detect molecular components of the odour, eliciting a series of neural responses that draw one’s attention to the coffee pot. But many details of that sequence are still unknown.

The number 10,000 has appeared in scientific literature and popular magazines, but only a few researchers have actually tested it. In the new study, the researchers say they suspected the human nose could smell many more than 10,000 scents, based on the fact that a typical nose has 400 olfactory receptors. The human eye has only three color receptors, and yet people can see up to 10 million colors, the researchers noted.

The relationship between the number of odorants that we can discriminate and the number of receptors that we have is unclear. Scientists who study smell have suspected a higher number for some time, but few studies have attempted to explore the limits of the human nose’s sensory capacity.

The human nose can distinguish at least 1 trillion different odours, a resolution orders of magnitude beyond the previous estimate of just 10,000 scents.

The human nose can detect one trillion different odours, far more than we previously thought, say US scientists. Until now, the long-held belief was that we can sniff out about 10,000 smells.
New estimates published in Science suggest the human nose outperforms the eye and the ear in terms of the number of stimuli it can distinguish between.


Scientists at the Rockefeller University, New York, set out to test the idea, which dates back to 1927 and was never scientifically investigated.

They devised experiments to see how good people are at distinguishing between cocktails of 128 different odour molecules, representing a large range of smells from grass to citrus. The molecules were mixed randomly in groups of 10, 20 or 30 to create unfamiliar smells.

The 26 people were then asked to identify a scent from three samples - two that were the same and one that was different.

Based on these results, the researchers used theory to extrapolate how many different scents the average person would be able to discriminate if they were presented with all the possible mixtures that could be made from the 128 molecules.

They estimated that the average person can discriminate between at least one trillion different odours with the nose, far more than can be detected by the eye or ear.

Posted by: Lusubilo A. Mwaijengo

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