There's no mistaking the odor of burning rubber for the fresh smell after a summer rain, but now new research shows the human nose can distinguish among many more odors than once thought.
People often say that humans can distinguish among only 10,000 different odors. But the new findings suggest that the nose can pick up on differences among at least 1 trillion odors.
"We debunk this old, made-up number of 10,000," said Leslie Vosshall, an olfaction researcher at the Rockefeller University in New York and a co-author of the study detailed in Friday's issue of the journal Science.
Testing whether people could smell 10,000 different scents or more would be an impossible task. So Vosshall and her colleagues tested a subset of these odors in different combinations.
The researchers created mixtures of 128 different scent molecules. Individually, the molecules gave off odors such as grass or citrus, but when they were combined, the blends smelled unfamiliar. Vosshall's team gave the volunteers three vials of scents — two of one scent along with a third, different scent — and told them to identify the unique odor. The volunteers repeated the process for more than 260 sets of vials.
The researchers counted how often the volunteers correctly identified the different vial, and extrapolated from their findings to estimate how many scents an average person could distinguish out of all possible mixtures. They concluded that humans can smell at least 1 trillion different scents. The actual number may be much higher, because there are more than 128 odor molecules, Vosshall said.
Previous research suggests that young, Caucasian women who are non-smokers and of normal weight make the best smellers, but the experiment described in Science didn't delve into demographics.