Something smells fishy in your underarm, and it’s not your sweat. Your antiperspirant may not only be killing sweat and odor, but the bacteria that cause it, according to a recent study by the National Institutes of Health. While that may be great for your significant other or officemates, it could alter what researchers call your “microbiome.” The findings were published in the journal Peer J.

Bacteria get a bad rap, but certain strains actually benefit the body. For example, staph bacteria living in armpits help defend against other types of harmful bacteria. A group of volunteers had their underarm bacteria tested daily for eight days, and here’s what the researchers found: Those who don’t normally use antiperspirant or deodorant had a type of bacteria called corynebacteria [Co-rynebac-teria] account for 62 percent of the skin’s microbes, while 21 percent were staph bacteria. Corynebacteria are partly responsible for body odor but also help protect against harmful bacteria.

The results were reversed among those who normally used deodorant or antiperspirant, with staph bacteria dominating rather than odor-causing bacteria.

Researchers said it’s unclear whether the bacterial changes caused by swabbing deodorants and antiperspirants have any negative effects on the body’s personal microbiome. More study is needed, but scientists say the findings build on the importance of paying attention to what we lather on the skin, which is the body’s largest organ. Lotions, gels and sprays can linger on the skin for days.

So spreading on that fragrant moisturizer or antiperspirant should keep you smelling fresh. Meanwhile, scientists plan to keep studying how those products affect the skin you’re in.