“Like the gut or the mouth, the human skin is covered with life. The precise composition of the skin biome influences its effectiveness as a defensive layer against pathogens, and contributes to bodily odors,” researchers wrote in a new study.
This has been known since the 1950s; however the extent to which human behaviors influence the composition of skin microbes is less known.
The study suggests that while antiperspirant may keep you dry, it also disrupts the bacterial “community” that resides in your armpits.
Julie Horvath, head of the genomics and microbiology research laboratory at the NC Museum of Natural Sciences, an associate research professor at NC Central, and corresponding author of a paper describing the work published in the journal, PeerJ, said in a statement:
“We wanted to understand what effect antiperspirant and deodorant have on the microbial life that lives on our bodies, and how our daily habits influence the life that lives on us.
“Ultimately, we want to know if any changes in our microbial ecosystem are good or bad, but first we have to know what the landscape looks like and how our daily habits change it.”
Standard deodorants are intended to kill off the microbes that cause body odor, and can include ethanol or other antimicrobials. This, ironically, appears to lead to an increase in microbial activity.
Antiperspirants, however, work by reducing the amount of sweat, which impacts on the moist environments preferred by microbes. This is potentially altering the entire evolutionary process of the natural bacteria.
Rob Dunn, a professor of applied ecology at NC State and co-author of the paper, said:
“Thousands of bacteria species have the potential to live on human skin, and in particular in the armpit.
“Just which of these species live in any particular armpit has been hard to predict until now, but we’ve discovered that one of the biggest determinants of the bacteria in your armpits is your use of deodorant and/or antiperspirant.”
The experiment consisted of 17 participants, and were monitored for eight days. Five went without deodorant or antiperspirant, while five regularly used deodorant, and the remaining seven regularly used antiperspirant.
All participants had swabs taken of their armpits between 11 a.m. and 1 p.m. The samples were then cultured to determine the abundance of microbial organisms growing on each participant, and how that differed day to day.
“We found that, on the first day, people using antiperspirant had fewer microbes in their samples than people who didn’t use product at all — but there was a lot of variability, making it hard to draw firm conclusions.
“In addition, people who used deodorant actually often had more microbes — on average — than those who didn’t use product.
“However, once all participants began using antiperspirant on days seven and eight, we found very few microbes on any of the participants, verifying that these products dramatically reduce microbial growth.”
According to NC State University:
“The researchers also did genetic sequencing on all of the samples from days three and six, to determine how antiperspirant and deodorant might affect the microbial biodiversity — the composition and variety of types of bacteria — over time.
“They found that, among study participants who hadn’t worn deodorant or antiperspirant, 62 percent of the microbes they found were Corynebacteria, followed by various Staphylococcaceae bacteria (21 percent), with a random assortment of other bacteria accounting for less than 10 percent.
“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. Staphylococcaceae are a diverse group of bacteria that are among the most common microbes found on human skin and, while some can pose a risk to human health, most are considered beneficial.”
However, the participants who regularly used antiperspirant had wildly different results. 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.
“Using antiperspirant and deodorant completely rearranges the microbial ecosystem of your skin — what’s living on us and in what amounts.
“And we have no idea what effect, if any, that has on our skin and on our health. Is it beneficial? Is it detrimental? We really don’t know at this point. Those are questions that we’re potentially interested in exploring.”
The findings highlight how human behavior can have a profound impact on the evolution of microbial organisms.
“Over evolutionary time, we would expect our microbes to co-evolve with us,” Horvath says. “But we appear to have altered that process considerably through our habits, from bathing to taking steps to change the way we look or smell.”