For many years it was believed that humans could detect about 10,000 different odors. A recent study published in Science (Mar. 21, 2014) provides evidence that, in fact, humans can discriminate more than 1 trillion olfactory stimuli.
Most odors are made up of a collection of “odorous” molecules. For example, the characteristic odor of a rose is made up of a mixture of 275 molecules, but only a small percentage dominates its odor. Scientists at Rockefeller University wanted to find out once and for all whether humans can detect subtle differences in mixtures of known odorous molecules. They recruited 26 subjects, 20 – 48 years of age, and 17 of them were females. The group included members of four races. Researchers created mixtures of 128 different scent molecules; individual molecules smelled like grass, citrus, peppermint, and so on, but when mixed together the mixtures had an unfamiliar smell. Volunteers received three vials of scent mixtures. Two of the mixtures were identical, while the third had a slightly different concentration of one of the molecules. The subjects were asked to identify which of the three vials had a different odor. This was repeated for more than 260 sets of vials of scent mixtures. The researchers counted how often volunteers correctly identified the vial with a different scent, and these data were extrapolated to estimate how many scents an average person can identify out of all possible mixtures of 128 scent molecules. The results indicated that the human nose can detect at least 1 trillion odors, and maybe more.
One wonders how the conscious and subconscious perception of odors influence our behavior. For example, evidence from other studies indicates that women select mates, in part, because of the way they smell. So if you are serious about finding a mate, avoid perfumes and colognes, these mask who you really are. A deodorant, however, is important, for the odor of stale perspiration is a turn-off.