Think for a minute about all the people stacked on top of each other in cities – not to mention dogs and cats and ferrets… and rats and cockroaches… and you’ll start to realize: this is microbial heaven.

Holly Bik went looking for this invisible, microbial world.

“It’s kind of a little bit disturbing,” Bik says. “Every surface we touch, actually our bodies, the human body, is covered in microbes - your skin, your gut, your mouth, your eyes have mites in them. Microbes are everywhere.”

Bik is now an assistant professor in the Department of Nematology at the University of California, Riverside. But back when she was a project scientist alongside biologist Jane Carlton at NYU, she worked on a study that tried to figure out something both simple and complicated – what’s the microbial situation on ATM keypads in New York City?

“The rationale behind the study was really just this lack of knowledge,” Bik says. “We don’t know anything about the microbes that live on ATM buttons… Everyone needs to go get cash at some point, especially in New York. So humans just sort of flock to these ATMs. And we’re all using them and we’re using them with a very specific part of our body, which is our fingers and our hands.”

So the scientists swabbed ATM keypads in Manhattan, Queens, and Brooklyn.

“We found seafood, we found chicken,” Bik says. “We found DNA signatures from people’s pets, cats and dogs... We found some novel microbes which aren’t very well characterized. They might be coming from the environment, they might just be fungal species which are kind of in the air floating around on dust and falling down. And then we also found a lot of bacteria that are associated with human skin. So we’re shedding microbes, and we’re using the ATMs. [So we found parts of] our skin microbiome too.”

What they didn’t find were many differences between the boroughs. The keypads in Manhattan and Queens and Brooklyn all looked pretty similar.

Urban areas actually have a whole microbial world that is powerful – and completely invisible.

You can’t get rid of it, no matter how hard you try. And Bik argues – you shouldn’t really want to:

“The idea that we need to be super clean and sterilized all the time is actually really bad for our health, because it can make our immune system just completely overreact when we do touch dirt or come into contact with pets. So in a way microbes are helping us because they’re helping our body not to freak out.”

But if you’re a city-dweller – or even a city-visitor – and you’re trying to convince yourself not to be scared by the invisible microbial world around you… consider Bik’s advice to those of us who are now grossed out by ATM keypads.

“I would say if you swab the dishes in your dishwasher, you would probably find similar pieces of DNA. Because DNA is really resistant, it survives... So you know, if you’re not washing an ATM keypad like you’re washing your dishes, then, of course, it’s going to be there. And I think that many of the surfaces that we come into contact with do have this kind of DNA and microbes and different things on them all the time... So just because we know about it on ATM keypads doesn’t mean it doesn’t exist in other areas of your life everyday. So don’t worry."