There’s nothing like being on a crowded subway in summer to make you consider body odor. Why do we smell in the first place? Why can some of us manage to get away with skipping a shower after the gym, while others reek after a quick walk to the park? And how does deodorant work (or not)?
As to why some people smell more or differently than others: age, diet, genetics and—yes—hygiene do play a role. But much has to do with bacteria. Sterile sweat has no scent. But the bacteria who thrive in the cozy moist environment of your armpits convert sweat molecules to smaller compounds, leading to bad odors. Depending on the type of bacteria that happen to live in your particular pits, the odors can range from sour to meaty to oniony to rotten egg-like. Deodorants work by killing some of the bacteria, by covering odors with perfumes, and, usually, by reducing the amount you sweat in the first place. But, as anyone who’s stood nose-to-armpit with a whiffy stranger on a summer subway knows, they don’t work perfectly.
Recently, British researchers made a discovery that furthers our knowledge of bacteria and the odor producing process—a discovery that may one day lead to more effective deodorants. The biologists, at the University of York, found that several species of Staphylococcus bacteria cause the formation of the smelliest compounds. So a relatively small number of bacteria species cause an outsize portion of smelliness.
But how do these bacteria make unscented sweat compounds so smelly?
“We had discovered that a small number of bacteria were able to produce the odorous chemical 3M3SH from an odorless precursor molecule that we secreted from the axilla glands in our underarm,” says biologist Gavin Thomas, co-author of the study published in the journal eLife. “We wanted to figure out how these Staphylococcal bacteria were able to achieve this feat and have been trying to figure this out over the last few years.”
The team eventually decoded a key step in the process: the structure of the transport protein that allows bacteria to recognize and consume sweat compounds. Understanding this protein means that, in theory, new deodorants could be developed to interrupt the process. Since it’s only a relatively small number of bacteria that produce the worst smells, those bacteria could be targeted while the others are left alone.
“It is definitely helpful to have a more complete view of the biochemical, enzymatic and genetic background,” says Chris Callewaert, a postdoctoral researcher at the University of California, San Diego, who studies body odor, of the new research.
But creating new deodorants—something the York team is not involved with—will likely not be easy.
“Bacteria are not only living on the skin epidermis, but also inside the skin,” Callewaert says. “If they find an ‘enzyme-blocker,’ it will still be difficult to supply it in the deeper skin regions, from where body odor formation starts.”
As to why we smell in the first place, Thomas says, “It is possible that the same bacteria have co-evolved with Homo sapiens as part of a mechanism to produce volatile signaling molecules—pheromones to be more precise—with roles in sexual attraction and mate selection.”
Over time, body odor has become taboo in most of the world, says Callewaert, whose own research involves looking at the potential of probiotic deodorants made out of “good bacteria.” In some places, people can even lose their jobs over their scent, he says.
“Bad smell is associated with bad hygiene,” Callewaert says. “At the same time, people with body odor—and certainly the ones that are aware of it—will wash themselves much more, use lots of deodorant and will change their clothes very frequently. So it is not about bad hygiene, but about the microbiome. It is simply not well understood by the public.”
And it has not always been so taboo. Deodorants and antiperspirants have only existed relatively recently in human history. While people have been using perfumes for thousands of years, the first bacteria-killing deodorant wasn't trademarked until 1888, and the first antiperspirant didn't hit the scene until 1903. It took clever advertising campaigns to convince Americans that these products were necessary, emphasizing the humiliation and romantic rejection faced by the smelly. But the manufacturers had major hurdles to overcome before deodorants became the $18 billion industry they are today. After all, some of our fairly recent ancestors seemed to have rather enjoyed the smell of a ripe armpit.
As Thomas says, “I recall Napoleon supposedly writing to Josephine when returning from the battlefield, ‘I am coming home—don’t wash.’”