Humans are able to distinguish between at least 1 trillion different odors, according to a recent study by Howard Hughes Medical Institute (HHMI) scientists looking to test the theory that humans can only discriminate between 10,000 odors.
"It's the generally accepted number," HHMI investigator Leslie Vosshall, who studies olfaction at the Rockefeller University, said in a press release. "Our analysis shows that the human capacity for discriminating smells is much larger than anyone anticipated."
Vosshall and colleagues were not entirely convinced that the 10,000 number - established in the 1920s without any supporting data - was accurate. Humans can see up to 10 million colors with just three light receptors, so why couldn't we smell more than 10,000 different odors with 400 olfactory receptors?
The study's team used 128 different odorant molecules to concoct their mixtures. Individually we might interpret these aromas as grass or citrus, for example, but by randomly combining 10, 20, or 30 of them they are unrecognizable.
"We wanted people to pay attention to 'here's this really complex thing -- can I pick another complex thing as being different?'" Vosshall explained.
The scientists presented their 26 volunteers with three scents at a time - two of them were the same; one was different. Participants then had to sniff out which one was the outlier. They did this 264 times.
After tallying how many subjects could correctly identify the scent that didn't belong, Vosshall's team extrapolated 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 their 128 odorants.
"I think we were all surprised at how ridiculously high even the most conservative lower estimate is," Vosshall says. "But in fact, there are many more than 128 odorants, and so the actual number will be much, much bigger."
Even though Vosshall is doubtful humans are exposed to that many smells on a daily basis, she notes that it doesn't hurt to be prepared.
"With a sensory system that is that complex, we are fully ready for anything," she said.
