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Study: Deodorant has significant effect on underarm microbes

Deodorant and antiperspirant affect the types of microbes that grow in the underarm.
By Stephen Feller   |   Feb. 4, 2016 at 10:22 AM

RALEIGH, N.C., Feb. 4 (UPI) -- Researchers found deodorant and antiperspirants have a significant effect on microbe populations in the armpit, but are unsure if the changes are good or bad.

The small study, conducted at North Carolina State University, found the two odor-reducing products each reduce the density and variety of microbes living in the underarm.

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The two have different effects on the body. Deodorant kills bacteria that ingest sweat and produce molecules responsible for underarm odor, while antiperspirants reduce the amount users sweat, preventing bacteria from having the reaction in the first place.

Researchers involved with the study said they hope to gain better understanding of how microbes are influenced by human genes and the effects of altering microbe populations on the human body.

"Using antiperspirant and deodorant completely rearranges the microbial ecosystem of your skin -- what's living on us and in what amounts," said Julie Horvath, head of the genomics and microbiology research laboratory at the NC Museum of Natural Sciences at North Carolina State University, in a press release. "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."

For the study, published in the journal PeerJ, researchers recruited 17 participants who were split into three groups: Three men and four women used antiperspirant; three men and two women used deodorant; and three men and two women did not use either product.

During the weeklong study, participants were asked to use the products the way they normally would on day one, before being asked to use nothing for days two through six. During days seven and eight, all participants were asked to use antiperspirants.

On day one, there was wide variability between participants' underarm microbial populations, although people who used deodorant on average were found to have more microbes in their armpits than people who don't regularly use either of the products.

By day six, the amount of bacteria on participants was comparable, though growth on people who normally use antiperspirant was slower to catch up. For the last two days, all participants saw microbe levels in their underarms dive when they started using antiperspirants -- which researchers said shows how effective the products are.

Researchers reported the types of microbes that grew on participants differed based on the products, or lack thereof, they normally used. For those who did not generally use either product, 62 percent of microbes were corynebacteria, which are partially responsible for the stench of body odor, 21 percent were staphylococcaceae, 8 percent were anaerococcus, and a "random assortment" of others accounted for about 9 percent.

People who'd regularly used deodorant or antiperspirant saw similar results: Both groups had about 60 percent staphylococcaceae and between 4 and 5 percent anaerococcus. Antiperspirant users had about 14 percent corynebacterium, leaving 22 percent of microbes as a random assortment, while deodorant users had 29 percent corynebacterium and 5 percent random microbes.

More research is needed to learn how and why the products affect microbe populations the way they do, as well as the effect, if any, on the body, researchers said.

"Within the last century, use of underarm products has become routine for the vast majority of Americans," said Julie Urban, assistant head of the genomics and microbiology laboratory at the NC Museum of Natural Sciences. "Yet, whether use of these products favors certain bacterial species -- be they pathogenic or perhaps even beneficial -- seems not to have been considered, and remains an intriguing area needing further study."

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