Sense of smell is strictly personal, study suggests

A person’s sense of smell may reveal a lot about his or her identity.

A new test can distinguish individuals based upon their perception of odors, possibly reflecting a person’s genetic makeup, scientists report online June 22 in Proceedings of the National Academy of Sciences.

Most humans perceive a given odor similarly. But the genes for the molecular machinery that humans use to detect scents are about 30 percent different in any two people, says neuroscientist Noam Sobel of the Weizmann Institute of Science in Rehovot, Israel. This variation means that nearly every person’s sense of smell is subtly different. Nobody had ever developed a way to test this sensory uniqueness, Sobel says.

Sobel and his colleagues designed a sensitive scent test they call the “olfactory fingerprint.” In an experiment, test subjects rated how strongly 28 odors such as clove or compost matched 54 adjectives such as “nutty” or “pleasant.” An olfactory fingerprint describes individuals’ perceptions of odors’ similarities, not potentially subjective scent descriptions.

All 89 subjects in the study had distinct olfactory fingerprints. The researchers calculated that just seven odors and 11 descriptors could have identified each individual in the group. With 34 odors, 35 descriptors, and around five hours of testing per person, the scientists estimate they could individually identify about 7 billion different people, roughly the entire human population.

People with similar olfactory fingerprints also showed similarity in their genes for immune system proteins linked to body odor and mate choice. This finding means that people with similar olfactory fingerprints probably smell alike to others, says study author Lavi Secundo, also a neuroscientist at the Weizmann Institute.

It has been shown that people can use smell to detect their genetic similarity to others and avoid inbreeding, says neuroscientist Joel Mainland of Monell Chemical Senses Center in Philadelphia.  

Sobel says that the olfactory fingerprint could someday be used to construct smell-based social networks. The test could also become a diagnostic tool for diseases that affect the sense of smell, including Parkinson’s disease, he says.

Administering scent tests can be cumbersome, so it will be hard to use such tests in the clinic without scent-generating electronic devices, Mainland says. But using scent perception to identify genetic markers is interesting, and from a security standpoint, he adds, an olfactory fingerprint would be very hard to copy or steal. “There might be applications of this that we haven’t thought of.”