The Scientist: Philip M. Tierno, Ph.D., professor of microbiology and pathology at New York University School of Medicine
The Answer: As disturbing as a public bathroom may be, the truth is, it’s very difficult to catch something from a toilet seat. In a way, the more it’s used by other people, the more often it’s cleaned—by their butts. People sitting on the seat or covering it with toilet paper means that the surface is constantly being wiped down. (More often, then, say, the stall door lock or the faucet handle.) And sitting in a sprinkle of a stranger’s urine, while disgusting, is unlikely to be dangerous, unless you happen to have an open wound on the back of your thigh. If there’s fecal matter on the seat, it gets a little dicier—not because you’re going to get a disease through your skin but because it might get on your hands.
There are more bacteria in 1 gram of fecal matter than there are or were people who have ever walked the face of the earth. That said, the only way that bacteria or a nasty stomach bug like norovirus is likely to make you ill is if enough of it gets on your hands and you then put your unwashed hands in your mouth, eyes or nose. So, just wash your hands and you’ll probably be fine.
In the highly unlikely event that something splashes up out of the toilet bowl and square onto your butt hole, wipe a little extra—and get the toilet paper wet if you can—to eliminate any organisms hanging about. They probably won’t make it up inside you, and if they were to, they’d probably be overtaken by your internal bacterial flora and immune system, but better safe than sorry. And you’ll be cleaner to boot, so win-win.
The water in the bowl is relatively clean, but if you want to prevent icky toilet splash, pre-flush any remnants from the last user, stepping back away from the toilet (especially an older, industrial toilet with a powerful flow) to avoid bacteria sent flying into the air. Then toss in a small wad of toilet paper into the fresh water to absorb and dampen any potential splash back.