healthHealth and Medicine

Your Toothbrush Probably Doesn't Contain Poo Matter, Reassuring Study Says

Johannes Van Zijl

Johannes Van Zijl

Johannes has a MSci in Neuroscience from King’s College London and serves as the Managing Director at IFLScience.

Managing Director

Brushing teeth

The study found microbes on toothbrushes matched those inside mouths and on skin, not our gut. Image Credit: Jose G Quintana/

In a world that is currently dominated by distressing and concerning news most days, it will come as a relief to hear a bit of good news from the scientific research realm. In case you have ever worried about this before, and probably many have, your toothbrush is slightly more hygienic than previously thought.

The good news is that the diversity of microbes living on your toothbrush likely comes from your mouth, face, or skin, and probably not from your gut. In other words, any concerns you may have had about those aerosol droplets from the toilet splash after a flush making their way onto your bristles while your toothbrush sits comfortably by the sink is probably not something you need to worry about.


"I'm not saying that you can't get toilet aerosols on your toothbrush when you flush the toilet," said Dr Erica Hartmann, senior author of the study, in a statement. "But, based on what we saw in our study, the overwhelming majority of microbes on your toothbrush probably came from your mouth."

Inspired by the question of whether toothbrushes stored in open areas within bathrooms might be impacted by flushing toilets that could release aerosol particles, the researchers from Northwestern University investigated the diversity of microbes found on toothbrushes that were mailed in by users in a project known as the Toothbrush Microbiome Project. Hartmann and her team named their study "Operation Pottymouth", and asked people to mail in their used toothbrushes alongside meta-information about their use and oral hygiene (how often they brush their teeth etc) and storage. 

In the study, published in the journal Microbiome, they extracted DNA from the toothbrush samples gathered through the Toothbrush Microbiome Project to assess what types of microbes lived on the brushes. They then sampled and compared the findings with a National Institute of Health catalog of microbial flora commonly found on and in different parts of the body of healthy people. 

"Many people contributed samples to the Human Microbiome Project, so we have a general idea of what the human microbiome looks like," said Ryan Blaustein, first author of the study. "We found that the microbes on toothbrushes have a lot in common with the mouth and skin and very little in common with the human gut."


"Your mouth and your gut are not separate islands," Hartmann added. "There are some microbes that we find both in the human gut and mouth, and those microbes are found on toothbrushes. But, again, those are probably coming from your mouth."

So, the toilet splash theory probably does not hold true. Your toothbrush likely does not contain a huge diversity of gut microbes that suggests they arrived there via fecal matter when you flushed the toilet after a number 2. But let's all keep the lids down when we flush just in case.

Interestingly, the study also found that individuals that reported having better oral hygiene practices had a smaller diversity of microbes on their toothbrushes overall.  

"If you practice good oral hygiene, then your toothbrush also will be relatively clean," Hartmann said. "But it's a small difference. It's not like people who regularly floss, brush and use mouthwash have no microbes and those who don't have tons. There's just a bit less diversity on toothbrushes from people who do all those things."


Furthermore, they also saw that those that had better oral hygiene practices also had more antimicrobial resistance genes in the microbe diversity they did have. The authors said this might be from microbes found in the air and dust present in bathrooms, as they did not match any human antimicrobial resistance genes. The study stressed that there is no need to be alarmed by the microbes living on your toothbrush and that unless advised otherwise by your dentist, people should not be reaching out to use antimicrobial toothpaste or toothbrushes.   

"By using antimicrobials, you aren't just getting rid of microbes," Hartmann said. "You are pushing the surviving microbes toward antimicrobial resistance. In general, for most people, regular toothpaste is sufficient."


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