Here’s the most disgusting thing that has ever happened to me in New York: I was at a fancy bar in SoHo, wearing brand-new clothes when I sat on a puddle of white puke. I have no idea how a regurgitated white Russian ended up on that leather couch. What I do know is that the vomit seeped through all the layers of fancy clothing I had on — including my underwear. I ran to the restroom and almost threw up myself.

Now, any time I come across a pool of vomit, I stop breathing and run away as fast as I can. And it’s not just me. The other day, at a Brooklyn subway stop smeared with barf, I heard a flip-flop-wearing woman shout: “Fuck! I almost stepped on it!” But would other New Yorkers agree with me that puke is the most disgusting thing in the city? Certainly, most of us have stumbled upon grotesque pools of bodily fluids on the sidewalk or subway, but maybe you’re more grossed out by cockroaches or you just can’t stand rubbing your arms against somebody’s sweaty armpit on a crowded train. Is it possible to create a scale of disgust that everyone can agree with?

Disgust is highly subjective: it’s influenced by experience as well as where and how we grew up. But there are certain things that gross all of us out pretty much across the board, and that has to do with how the emotion is wired in our brain. “Disgust is an ancient instinct that we learn to protect ourselves against things that might kill us,” says David Ropeik, a consultant in risk perception. “So, if it smelled bad, it tasted bad, or it looked bad, that was a warning signal not to put it in our body.”

Because disgust is a survival mechanism, most people are revolted by things that might make us sick or carry disease, says David Pizarro, an associate professor in the psychology department at Cornell University, who studies disgust. (Think: urine, feces, blood, pus, as well as rotten meat and parasites.) But there are exceptions. “The feeling of disgust is not perfect,” Pizarro says. While most people find bodily fluids revolting, tears don’t have the same effect. And shaking hands is one of the prime ways that people spread disease around, but we’re not disgusted by it. (That’s because “hands don’t have reliable disease cues,” Pizarro says, unless you see someone sneeze into their hands before shaking yours.)

Culture also plays a huge role. People in Asia eat crickets, locusts, and scorpions, but most Westerners gag at the idea. There is a benefit to that flexibility, Pizarro says. “As human beings, we’re raised in very, very different environments, and if the disgust response to food, for instance, was so strong and innate, we wouldn’t be able to adapt to the environments and eat all of the things we can eat.” We can also learn how to get over our repulsions. For instance, a 2008 study published by Paul Rozin, a professor of psychology at the University of Pennsylvania and one of the leading experts on disgust, showed that first-year med students become less sensitive about dissecting cadavers after doing it for a while. If you shovel cow dung for a living, the sight and smell of poop might not affect you as much.

Curiously, disgust isn’t observed in newborns. “When have you ever seen a toddler get disgusted by their diaper, right? They just don’t!” says Pamela Dalton, who researches smells at Monell Chemical Senses Center. Instead, children develop a sense of disgust in the first few years of their life — possibly as they’re potty trained, says Rozin. “The best idea is that toilet training starts it and that feces are the original disgust,” he says. Still, just like puberty, disgust seems to be “biological and hardwired,” Pizarro says, as everyone sooner or later will be grossed out by something.

What that something is also depends on context and control, says Ropeik. Smelling sweat on a crowded train might make you go “ew,” but a whiff of it at a gym is just fine. If you’re stuck somewhere and can’t escape the bad smell or sight, that also has an impact. “The smell of geyser in Yellowstone is cool. The smell of a geyser in an elevator from a guy next to you is not,” Ropeik says. “Same chemical.”

When I told Rozin that I was trying to rank the most disgusting things in New York City, he said that he’s not into rankings. “There are lots of disgusting things, and people vary on how disgusting they are,” Rozin told me. Pizarro agrees that it’s impossible to come up with a definitive list. Though it’s true that certain things, like poop, disgust people more than others, “there’s a lot of noise and individual differences,” he says. When Pizarro’s daughter turned five, for instance, she thought blood was the most repulsive thing, but Pizarro doesn’t think blood is that bad. Lots of people hate cockroaches but think ladybugs are cute. I find ladybugs just as disgusting. “That’s why we can’t do the ranking!” Pizarro told me.

Still, we know that bodily fluids, rotting food, and the like turn people off. And we know that certain attributes make things even grosser. For example, smell. The olfactory bulb — the area of the brain that processes odors — is tightly connected to the amygdala, which is where the brain reacts emotionally. That’s why we think that smells are “emotionally evocative,” says Dalton. “You may not visually like the look of all the garbage out there, but when it’s combined with the smell that you get in the summertime, it’s exponentially worse,” she says. “Smells by themselves can be disgusting, but I think they can also enhance the disgusting nature of other things.”

So, based on all this information on what repels humans and how disgust works, here’s what my (very personal) ranking of the most disgusting things in New York City looks like — from bottom to top.

Dog turds on the sidewalk

“Disgust to feces is universal,” says Rozin. And that makes sense: poop smells bad and carries disease. However, I’m placing dog turds at the bottom of my list because I grew up in Rome, where I stepped on excrements more times than I can count. I’m used to it, and it doesn’t bother me that much. Plus, that’s what the New Yorker speed-walking is all about: speeding past a big pile of poop before the smell hits your nostrils.

Crowded subways

Things can get pretty icky on the train during rush hour — especially if riders are sweaty or sneezing and coughing all over. Sweat is definitely a bodily fluid most people are repelled by. Plus, it has the smell component, which makes the grossness stronger. And because on a crowded subway, you’re essentially stuck, the sense of disgust is heightened. “Control is a huge factor for our safety, so whenever you’re exposed to something that could be bad for your health and you can’t do anything about it, it’s grosser,” Ropeik says.

Still, having lived in big cities my whole life, I’m not put off by crowds, so I can deal with being crammed in a can traveling at high speeds underground.

Bed bugs, scabies, cockroaches

Parasites are disgusting to many of us because they might spread diseases, Pizarro says. Our brains probably just learned to stay away from insects because they might make us sick or give us cues that food is rotten. But a lot of our disgust with bugs is cultural or based on experience, he says. Thankfully, I’ve had few encounters with these pests in New York. I’ve only heard of one friend who had scabies, a type of skin mites, in her dorm in the city. Though I had a very mild bed bug infestation in one Manhattan apartment I lived in, pest control only found a couple of the critters on my roommate’s bed, not mine. Plus, these insects scare me more than revolt me. And this is a ranking about disgust, not fear.

Rats

Similar to parasites, many of us find rats gross because of how dirty and dangerous they are. Rodents can transmit the plague, salmonella, hemorrhagic fevers, as well as a host of other horrible sounding diseases, according to the Centers for Disease Control and Prevention. In New York City, you’ll likely find them scurrying along the sidewalk, or inside garbage bags gnawing at pieces of rotten food. In this list, rats are ranked as more disgusting than bed bugs, scabies, and cockroaches because I’ve had a really scarring experience with them: one rat found its way into my boyfriend’s apartment one night, and he killed it with a tennis racket. Meanwhile, his roommate’s terrified cat looked from afar.

Garbage leak on the sidewalk

New York City is famous for asking residents to pile their garbage on the sidewalk for collection — sometimes leading to piles of trash that are taller than people. This is disgusting, especially in the summer: those sticky, brown puddles of trash leak baked in the sun are bound to reawaken that ancient survival instinct that feeds into the emotion of disgust. Rotting food is almost universally considered revolting, according to Pizarro. The putrid smell also reinforces our sense of disgust. “The fact that you’re inhaling these chemicals into your body makes you feel more vulnerable and more disgusted,” Dalton says.

Vomit in public places

I think the first-person story at the beginning of this article explains why puke wins the prize for most disgusting thing to me in New York City. The good news is, I can get over this by doing exposure therapy, Ropeik says. Just like we can rid of phobias by gradually getting exposed to the things that terrify us without anything bad happening, we can learn to stop being revolted by vomit, cockroaches, and dog poop. “You’re exposed to the negative stimulus without the same negative feedback and what happens is, your brain learns that that stimulus can happen without the negative feedback,” Ropeik says. “That doesn’t weaken the memory. It adds something else to the memory.”

“That’s exposure therapy,” he adds. “People get to pay to do that. Or if you ride the subway in New York, you do it by yourself for free.”