Deodorant and Antiperspirant Mess With Your Microbes

As a scientist fascinated by microbes, Julie Horvath wants to know as much as possible about what’s living on her skin. So when she and a few colleagues swabbed their armpits and bellybuttons and let the bacteria incubate for a couple days, she was alarmed at what she saw.

“My plates were blank,” she says, referring to the petri dishes on which the samples were cultured. “I was a little bit freaked out, because I’m supposed to have microbes on my body.” She thought her clinical-strength antiperspirant might be the cause of the clean plates. “If I wear it in my armpits and it’s influencing whether I have bellybutton microbes, maybe it’s getting on other parts of my body and wiping out some of the life there, too,” she says.

Horvath, who is head of the genomics and microbiology research laboratory at the North Carolina Museum of Natural Sciences and an associate research professor at North Carolina Central University, wanted to find out if deodorant and antiperspirant were linked to different patterns of bacterial growth in the armpits. So she and a team of researchers at different institutions took a closer look at armpit bugs in a new study published in the journal PeerJ.

First, here’s a quick perspiration primer. When we smell bad, that’s because microbes in certain warm, sweaty areas are producing body odor. Antiperspirants try to stop sweating, typically through aluminum-based salts that stop up apocrine glands, or sweat glands. “If you don’t sweat as much, there’s not as much food for the microbes, there’s not as much microbe growth and therefore you don’t have that much body odor,” says Horvath. Deodorant is designed to kill those odor-making bacteria, so it usually contains antimicrobial agents or ethanol. It’s also easier to wash away than antiperspirant.

The new study finds that these solutions to smelliness actually affect the type of bacteria, and how much of it there is, on your armpits.

The researchers recruited 17 people who fit into one of three categories: people who wore antiperspirant, people who wore deodorant and people who abstained from armpit products altogether. For eight days, they swabbed their armpits around lunchtime.

On the first day, everyone followed their preferred underarm routines. On days two through six, everyone took a break from underarm products. On the final two days of the experiment, everyone used antiperspirant.

To figure out which bugs were growing in which pits, researchers cultured the samples in the lab.

At the start, antiperspirant wearers had fewer microbes—and deodorant wearers had more—than people who didn’t use products. After everyone had abstained for a few days, thought, everyone had pretty similar colonies. But when everyone started using antiperspirant near the end of the experiment, microbes were pretty much wiped out on all armpits, indicating that antiperspirants are really good at their job.

Interestingly, the types of bacteria found in the samples varied based on the product worn. People who didn’t use products had pits populated mostly by Corynebacterium—the kind that both produces body odor and helps defend against pathogens. Those who used products tended to have more Staphylococcaceae, which are typical skin microbes that can be either beneficial or dangerous.

Armpit bug colonies are not a popular area of focus in scientific literature, so the small-sized, early research can’t suggest which armpit regimen is healthiest. “Antiperspirant wearers have a lot more variation of the microbes on their skin than a deodorant wearer,” Horvath says. “From a lot of other microbiome studies, we know that variation is important and probably healthier,” so antiperspirants could potentially have both positives and negatives. “There’s so much more that we need to learn,” she says.

After doing the research, Horvath stopped wearing clinical strength antiperspirant and is now dabbling with natural deodorants that don’t contain aluminum. (“They don’t work as well,” she adds.) Though there are too many unknowns to recommend a bug-friendly pit regimen, “it’s really exciting to think about what some of the potential possibilities are,” she says.