Fair warning: this story is going to make you want to buy a new toothbrush - and then hide it from your housemates.
New research has found that if you share a bathroom, it is very likely someone else's poo is on your toothbrush. This isn't just disgusting, it can also make you very ill.
"The main concern is not with the presence of your own fecal matter on your toothbrush, but rather when a toothbrush is contaminated with fecal matter from someone else, which contains bacteria, viruses or parasites that are not part of your normal flora," said research Lauren Aber of Quinnipiac University.
Aber examined 135 toothbrushes from college students using communal bathrooms shared by an average of five people. The toothbrushes were then tested, and scientists found at least 60 per cent were contaminated with fecal bacteria - even if they were rinsed with mouthwash or hot water and even if people stored them with a toothbrush cover. There is an 80 per cent change the bacteria found on the toothbrushes came from a different person.
This happens because fecal matter from flushing a toilet can be sprayed up to six feet - and toothbrushes can then serve as a way for bacteria to be transmitted.
"Using a toothbrush cover doesn't protect a toothbrush from bacterial growth, but actually creates an environment where bacteria are better suited to grow by keeping the bristles moist and not allowing the head of the toothbrush to dry out between uses," Aber said.
The research was presented at the American Society for Microbiology on Tuesday.