Though it’s not known whether this would affect human positively or negatively, researchers are tired of such changes to human microbiome, the trillion of bacteria and other microbes that inhabit the human body.
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“Thousands of bacteria species have the potential to live on human skin, and in particular in the armpit”, says co-author Rob Dunn, a professor of applied ecology at NC State. While there’s no evidence that this is necessarily harmful to human health, the researchers say it’s possible that these natural microbes serve a beneficial goal, and if they do, it could mean we’re doing ourselves no favours by altering them.
“Using antiperspirant and deodorant completely rearranges the microbial ecosystem of your skin – what’s living on us and in what amounts”.
People who did not use either product had a higher concentration of corynebacteria (62 percent), a group of bacteria that is related to body odor. Stopping the use deodorant or antiperspirant similarly encourages the presence of Staphylococcaceae over Corynebacterium, but the two products have differential modes of action that result in different effects on the bacteria living in the armpit.
Horvath became interested in antiperspirants’ effects after she and her lab colleagues ran an experiment among themselves: They took swabs of their armpits, then cultured the samples to see what microbes were dwelling there.
Things got more complicated when the whole study group stopped using all underarm products: By day six, all volunteers showed similar amounts of bacteria in their armpit swabs – but the type and diversity of those bacteria varied widely.
This pattern was reversed among participants who typically use antiperspirant or deodorant.
On day one, each followed their normal hygiene routine and sprayed deodorant, antiperspirant or used nothing. This verified that the use of these products reduces microbial growth. Deodorant users actually had the most bacteria. They instructed participants not to use any products for the next five days to sample which kinds of microbes would grow back. Sixty percent of their microbes were Staphylococcaceae, only 14 percent were Corynebacteria, and more than 20 percent were filed under “other” – meaning they were a grab-bag of opportunistic bacteria.
Corynebacteria are partially responsible for producing the bad smells we associate with body odor, but they are also thought to help us defend against pathogens. While most of Staphylococcaceae bacteria are believe to be not harmful, some can still pose threat to human health. We really don’t know at this point.
But the fact that the products we use can so dramatically alter the composition of these bacteria in our armpit microbiome could potentially have significant consequences, the researchers report in PeerJ.
The study follows another paper that observed that armpit microbes in primates-which are vastly different than those of humans- have evolved over time in conjunction with the primates they live on.
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“One exciting finding was that the non-human primates were more covered in faecal and soil associated microbes, which we often view as dirty”, said Horvath.
