Bacteria-busting toothpastes that help prevent cavities in your teeth could be making small dents in the community of microbes in your gut—possibly allowing antibiotic-resistant bacteria to fill in—preliminary data suggests.

In a small study, women who switched to brushing with toothpaste that contained the antimicrobial triclosan saw a troubling shift in the microbes in their guts as well as a slight change in drug resistance, Stanford researchers report.

The data is preliminary—it has not been peer-reviewed or published in a journal yet—and the study was small, including women and infants from only 39 households. But, the findings fall in line with several other studies that found that triclosan and other common antimicrobials can cause subtle disruptions in all-powerful gut microbiomes.