The first time I saw someone sit on a public toilet, I screamed.

My friend and I were in a McDonald’s restroom, casually chatting, when she lowered her pants and sat on the toilet. “What are you doing?” I shouted, suddenly panicky. I told her she should squat on the seat or at least cover it in toilet paper: public toilets are dirty! She shrugged my concerns away and kept doing her business. But then I started asking other friends: Do you sit down on public toilets? To my shock, the answer was always yes.

I never sit down on a public toilet. If I really need to go, then I cover it with mounds of toilet paper — if the seat is clean. (If it’s covered in pee, I just hold it until I’m home, or until I find a public restroom that’s not as disgusting.) That’s how my mom taught me. And to this day, I am a squatter. Or as Mary Roach called people like me in a delightful 2000 op-ed, I am one of the “ladies who spray.” As it turns out, my fear of public toilets has very little to do with the actual risk of getting an infection — which is minimal — and more with how our brains are wired. When assessing risk, facts don’t matter. Feelings do.

I’m saying “our brains” deliberately because I’m not alone. A 1991 survey of 528 British women found that 85 percent of them crouched over public toilets, 12 percent used toilet paper, and only 2 percent sat directly on the seat. (Of course, this survey is from 27 years ago and attitudes do change with time.) I won’t lie — hovering above the seat, trying hard to center the bowl, is an uncomfortable way to urinate. It has led to embarrassing accidents. One time, at a classical music concert in a church, I peed on my grey trousers, creating a pretty noticeable dark stain. (I ended up splashing myself with even more water before exiting the restroom, so I could blame a “sink accident” for my wet pants.) But I’d rather deal with this than have my naked thighs touch the seat where other people’s butts have rested.

When I found out my friends, coworkers and, appallingly, my editor all sat directly on toilets, I went to the scientific literature to show them why I was afraid. And I did find some terrifying cases. In 2003, an eight-year-old girl “most probably” got gonorrhea from a dirty airplane toilet, according to the case study. It didn’t seem that the girl had been sexually abused, the study says, and she said that her hands had gotten dirty as she wiped the seat with toilet paper before going. Using the same hands to wipe herself might have led to the infection.

Another paper found that Salmonella can survive in toilets used by infected people, up to four weeks after their diarrhea has stopped. Stomach flu viruses can also spread from toilets where sick people vomited, according to a 1989 study looking into an outbreak on a cruise ship. Swabs of public restrooms have revealed 3.3 percent of hospital toilet seats host the antibiotic-resistant bug Methicillin resistant Staphylococcus aureus (MRSA). And a 1979 paper titled “The Gonococcus and the toilet seat” — which sounds like a great children’s book — found a variety of microorganisms on the seat of public restrooms, including yeasts and Streptococcus bacteria, which can cause different types of infections.

These are cringe-worthy findings, but the risk of actually getting sick by sitting on a public toilet is basically zero. At least that’s what several microbiologists I spoke to told me. “Toilet seats are one of the cleanest things you can find in a restroom, that’s for sure,” says Charles Gerba, professor of microbiology and environmental sciences at the University of Arizona. Gerba told me that there’s 200 times more fecal bacteria like E. coli on a cutting board than on your home toilet seat. That’s because we disinfect toilets more than anything else in our homes. Office restrooms are also cleaned once a day, and therefore safe, Gerba says.

Bacteria don’t fare very well on a cold, dry, plastic toilet seat. And anyway, these bacteria have to enter your body somehow. You’d have to have a wound on your thigh, and get that wound infected, to contract something off a toilet seat. The thing to worry about is your hands: If you touch a stall latch that’s colonized by dangerous bugs, and then say, bite your nails, those bacteria could get inside you via your mouth. (That’s why you should always wash your hands after going to the loo.)

In fact, as I was reporting the story, I exasperated at least one microbiologist with my toilet-related disease fears. “It’s unfounded paranoia,” Jack Gilbert, faculty director of the Microbiome Center at the University of Chicago, told me, losing his patience. We’re much more likely to die from lifestyle factors — eating unhealthy food and not exercising — than we are catching anything off a toilet seat, Gilbert says. “People are killing themselves all day every day and yet they’re paranoid about a freaking toilet seat. It’s just the most ridiculous thing I’ve ever heard of.”

Gilbert says his son once dropped a toy in a urinal at a gas station off the highway somewhere in Massachusetts. He picked up the toy, washed it off, and gave it back to his son. His friends lost it: “Everyone was like, ‘Oh my god! That’s disgusting! You’re getting your kid infected,’” Gilbert says. “By what?”

Gilbert is right — but facts don’t speak convincingly to fear. (If my hypothetical future son drops his toy in a urinal, by the way, too bad for him.) That’s totally normal, according to David Ropeik, a consultant in risk perception and author of How Risky Is It, Really? Why Our Fears Don’t Match The Facts. “Risk is not a statistical number or a scientific formula,” he says. “It’s how we feel.” Just ask people who keep worrying (unnecessarily) that an out-of-control Chinese space station will fall on their heads.

Our brains, Ropeik says, rely a lot on instinct when we have to assess risk. For instance, if we find something disgusting, we try to avoid it. We evolved that way to stay away from things that might make us sick or kill us. Or, as Ropeik says: “Don’t eat things that smell like shit because you could die.”

There’s also another psychological factor at play, called loss aversion, which means that people care more about avoiding loss than about potentially getting something. Imagine entering a bathroom stall, where there’s toilet paper on the floor, maybe some drops of urine on the seat itself. That sight confronts us with an imminent loss — in this case, the possible loss of health, Ropeik says. When that happens, the potential bad outcome gets emotionally magnified, so we worry about losing our health more than we value emptying our bladder. It doesn’t matter how low the odds of getting an infection are.

Ropeik admits that there are exceptions: “If you really gotta go, to hell with this stuff, man. You’re gonna sit down.” But the irrational fear of a toilet seat is a great example of how our brains are wired to perceive risk, based on feelings. We assess all kinds of risky situations this way, and when we ignore the facts, the consequences aren’t always positive. “This is a warning, to think with our heads a little more and our guts a little less,” Ropeik says.

As for toilet seats, since the consequences aren’t serious — except maybe getting some pee on my pants — I’m going to keep doing what my mama taught me years ago. But don’t worry, I promise to wipe the seat clean.