Here's the bad news: Public bathrooms are dirty. Bathrooms, just like essentially any other place on the planet people visit regularly, are filled with bacteria and germs, despite all efforts to maintain cleanliness.
A study published in the journal Applied and Environmental Microbiology found that although an extraordinary amount of bacteria can be found in a public restroom, most of the bacteria dies, because the bathroom isn't an ideal space for bacteria to thrive and grow. The researchers found an average of 500,000 bacterial cells per square inch living on bathroom surfaces.
"The restroom isn't that dangerous," Jack Gilbert, a microbiologist at Argonne National Laboratory in Illinois and co-author of the study, told Live Science. "The organisms which can grow there have a very low probability of being able to cause an infection."
Gut bacteria from feces or vaginal bacteria can be found on toilet flush handles, and sometimes these handles have bacteria from soil or dirt on them. This comes from those individuals who like to flush with their feet, according to PBS' Gross Science.
"Fecal bacteria are less hearty than bacteria found on the skin, and die off faster when exposed to the cool, dry, oxygen-rich environment of a public restroom," Sean Gibbons, a graduate student of biophysical science at the University of Chicago, told HealthDay. "Bacteria associated with skin are more able to persist. Over time, they win out."
All in all, public restrooms contain no more bacteria than the restroom inside your home. While some of the bacteria inside public restrooms have the potential to make you sick, much of it poses no immediate health threat, and it is not likely that you'll catch a sexually transmitted disease from a public bathroom.
"To my knowledge, no one has ever acquired an STD on the toilet seat — unless they were having sex on the toilet seat!" Abigail Salyers, president of the American Society for Microbiology, told WebMD.
h/t Live Science