Good news: The bacteria on your toothbrush primarily reflect your mouth—not your toilet. Researchers at Northwestern University analyzed microbial communities on used toothbrush bristles and found they closely resembled microbes typically found in the mouth and on the skin. This held true regardless of storage location, whether behind a closed medicine cabinet door or out in the open by the sink.
The study's senior author, Erica Hartmann, PhD, initiated the research after hearing worries about toilet flushing creating aerosol particles that could contaminate toothbrushes. Her team playfully dubbed it “Operation Pottymouth.”
"I'm not saying you can't get toilet spray on your toothbrush when flushing," Hartmann explained. "But our study shows the vast majority of microbes on your toothbrush likely originate from your mouth."
Collecting Samples
To gather toothbrushes, Hartmann's team ran the Toothbrush Microbiome Project, inviting participants to submit their used brushes with metadata. They extracted DNA from the bristles to profile microbial communities, comparing them to those cataloged in the NIH's Human Microbiome Project, which maps microbes across the human body.
“Toothbrush microbes closely match those in the mouth and on skin, with little resemblance to gut flora,” Hartmann noted.
"The mouth and gut aren't isolated," she added. "Some overlapping microbes exist, but on toothbrushes, they most likely come from your mouth."
Cleaner Mouth, Cleaner Brush
The team assessed microbial diversity on the brushes. Those from individuals with strong oral hygiene—regular flossing and mouthwash use—showed lower diversity.
"Good oral hygiene keeps your toothbrush relatively clean," Hartmann said. "The difference is modest: brushes from diligent flossers and brushers have slightly less microbial variety, not a complete absence."
Interestingly, brushes from these individuals had marginally more antimicrobial resistance genes, likely from bathroom air or dust rather than the body, per Hartmann.
Hartmann advises against alarm over toothbrush microbes. Unless your dentist recommends otherwise, skip antimicrobial toothpastes or brushes.
"Antimicrobials don't just eliminate microbes—they promote resistance in survivors," she cautioned. "Standard toothpaste suffices for most people."
