How many different smells can humans detect? Way more than you might think.

For years, scientists have pegged the number at around 10,000. But for researchers at Rockefeller University and the Howard Hughes Medical Institute, that number just didn't pass the smell test. So they gathered up some scent vials and some sniffers and arrived at a mind-boggling new estimate. They say the human nose can smell one trillion different odors.

“Our analysis shows that the human capacity for discriminating smells is much larger than anyone anticipated,” Dr. Leslie Vosshall, a biochemist who studies olfaction at the university and one of the researchers responsible for the new research, said in a written statement. “I hope our paper will overturn this terrible reputation that humans have for not being good smellers."



Vosshall and a colleague presented a group of 26 men and women with complex odor mixtures made from 128 different odorant molecules. The group sniffed three scent vials at a time and determined which scent differed from the other two.

What did the researchers find?

The men and women correctly distinguished between the odors whose contents differed by more than 50 percent. Then, by extrapolating from the number of all possible odor molecule mixtures, the researchers arrived at that new 10-digit shocker. They said their estimate is probably on the low side, given that odors can contain many more molecules than the mixtures used in the study, and the molecules can be combined at different ratios. Get a whiff of that.

One of the test vials that the subjects sniffed in the study.

“I think we were all surprised at how ridiculously high even the most conservative lower estimate is,” Vosshall said in the statement. “But in fact, there are many more than 128 odorants, and so the actual number will be much, much bigger.”