How much you smell depends on how often you bathe, but precisely how you smell depends on your genes, a new study suggests. The body odors of identical twins are significantly more similar than the scents of unrelated people, researchers in Switzerland have found. The results could pave the way for new tools to diagnose disease or identify people based on scent.
Body odor emanates from a chemical reaction between bacteria on the skin and sweat, a secretion that itself is odorless. BO plays a role in mate selection among mice, and some experiments have suggested its importance for human mate selection as well (ScienceNOW, 18 June 2004). Among the most prevalent chemicals in body odor are at least 24 kinds of carboxylic acids. But it wasn't known how much of each of the various acids a person produces, says lead researcher Andreas Natsch, a biochemist for the Givaudan fragrance company in Dübendorf, Switzerland.
To test the role of genetics in body odor, Natsch and a colleague recruited 12 pairs of identical twins: seven sets of sisters and five sets of brothers. Because such twins develop from a single fertilized egg, they have identical genes unless a mutation occurs. The researchers gave each pair of twins cotton pads to wear in their armpits while they exercised for about an hour. After the exercise, the researchers collected the pads and treated them with the same bacterial enzyme to ensure that all the sweat samples were processed in a virtually identical fashion. The twins then repeated the process on another day.
Next, the researchers used a combination of gas chromatography and mass spectrometry to isolate the chemicals each sweat sample produced. They checked each chemical against previous records to ensure that it was an actual body product and not from any lingering trace of perfume or deodorant. By graphing how much of certain carboxylic acids each person produced, the researchers could identify patterns among the twin pairs. Body odor samples taken from the same person on the same day were most similar; those taken from the same person differed only slightly by day. But the pattern of carboxylic acids present in twins' body odors was 10 times more similar than the pattern of acids in unrelated subjects' odors, the researchers reported on Tuesday in the Journal of the Royal Society Interface. "For me, that's not very surprising," Natsch says. "Twins look the same, they smell the same."
Nevertheless, the finding could open the way for other advances. For example, researchers can now see if body odor reflects other conditions, says Craig Roberts, a biologist at the University of Liverpool in the United Kingdom: "It's important because it might help with noninvasive diagnosis of disease and potentially for biometric technology using genetically unique and distinct odors."