The B.O. Wheel. Click here for details.
They say you are what you eat, and when it comes to B.O., it's true. Body odor can be heavily colored by diet and also by the fragrant beauty products that we use. For this reason, one of the biggest challenges faced by odorprint researchers is to ferret out which chemicals constitute the "primary odor"—the root B.O. bouillon that can't be altered by diet and perfume. When I ran the results of my family experiment past George Preti, a smell researcher whose odorprint work has been funded by the Defense Advanced Research Projects Agency, his main criticism was that several of the odorants used to build my family tree were probably environmental. For example, my cousin Ricky and my uncle both had linalool on their hands, a ubiquitous fragrance compound used in soaps, shampoos, and detergents. But Preti conceded that the notion that I might smell more like my dad than my mom was not outlandish. Unlike genetics, he said, odor inheritance is "not a 50-50 mix."
It may not be surprising to learn that B.O. does indeed vary by gender—a recent study claimed that men smell like cheese while women smell of grapefruit or onions. It also reflects age: Preti's lab has found several odorants that increase with advancing years, such as the aldehyde nonanal. (This is not the molecule others have implicated in "old person smell.") There may even be racial differences in primary odors: Asians, for example, have fewer apocrine sweat glands than blacks or whites. In a new book about scent called Headspace, Amber Marks reports that in the 1990s a British electronic-nose company was approached by South African police and asked for the "odor signature" of black people. The company refused, but an employee told Marks that they could have derived such an ethnic odor-type if they'd tried.
If the prospect of a racial B.O. taxonomy gives you the willies, the history of smell discrimination offers no comfort. In the 19th century, Finns, Eskimos, Jews, and others were judged by vigilant European doctors to possess a characteristic unpleasant smell. (Asian docs thought Europeans were the foul ones.) Blacks were thought to be at greater risk of shark attack due to their "ammoniacal" odor. Blondes were said to smell "musky." The old, like "dry leaves." Lunatics, "fetid and penetrating." In 1829, a French scientist proposed a new smell-based forensic identification method but ran into problems discriminating dark-haired women from fair-haired men. Today we know these odor classes are absurd; humans can't even smell the difference between their own B.O. and that of a chimpanzee. But there are some broad patterns to B.O. flavor—for a visual representation, see this chart.
In any event, a new era of odor profiling may soon be upon us. Furton foresees a day when crime scene odor evidence might help cops establish a dossier: fiftysomething Irish-American male, wears Axe body spray, loves garlic. If cops had a suspect, they could trail him and covertly collect an odor sample using a scent capture contraption without touching him or asking permission.
While for centuries our B.O. obsession has focused on preventing its unwelcome trespass, today's worry may be in protecting our right to "odor privacy." For one thing, a body smell may convey private medical information: Both Preti and Furton are seeking the smell signatures of cancer and diabetes, and Furton is studying the odor differences between depressed and nondepressed individuals. Unlike DNA-rich blood or saliva, scent cannot be withheld from authorities because—alas—there is no "off button" for B.O. And, indeed, scent surveillance is already in use. In 2007, Der Spiegel reported that German authorities had collected scent samples from activists in advance of the G8 summit.
Privacy hurdles aside, the odor chemists' greatest challenge may be in overcoming our mistrust of smell. Odors can linger, sometimes for days, and they are invisible, so it can be hard to pin down their origins. An old grade-school maxim—"he who smelt it dealt it"—illustrates the risks in making accusations based on olfactory evidence. At this point, it's not clear that odor science has the tools to move past this folk wisdom.