Turns out you can’t just put a piece of plastic in your eye every day and expect everything to stay the same. New research shows that wearing contact lenses could significantly change the bacteria of the eye’s surface, making it more susceptible to infection.

Scientists from New York University’s School of Medicine presented this work Sunday at the American Society for Microbiology’s annual meeting. The study has been submitted, and the researchers are waiting to hear back on publication. They analyzed swabs from nine contact-wearers and 11 non-wearers to determine the number and type of bacterial species that lived on the surface of their eyes—the eye’s microbiome. The researchers also analyzed the bacteria on the skin just below the eye.

In people who wore contacts, the surface of the eye was much more similar in its bacterial makeup to the skin under the eye, while in non-contact wearers, the two were more differentiated. Specifically, contact-wearers had higher numbers of four species: Lactobacillus, Acinetobacter, Methylobacterium, and Pseudomonas. This microbiome disruption could explain why people who wear contacts are more likely to get some kinds of eye infections, including corneal ulcers, which, incidentally, have been linked to Pseudomonas bacteria.

“It’s not like all contact-lens wearers get more infections, it’s simply that a different type of bacteria has colonized and is living on the surface of their eyes,” says Lisa Park, a study co-author and clinical associate professor in the NYU School of Medicine’s department of opthamology. “It’s shifted a little bit. And the question then is: Does that predispose them then to getting certain types of infections?”

Infections often come when people don’t take proper care of their lenses—sleeping in them overnight, or not cleaning them well or often enough. According to one 2010 study, while 86 percent of contact-wearers thought they did a good job caring for their lenses, only 32 percent showed “good compliance.” Forty-four percent did average, and 24 percent were “noncompliant.”

“You put a contact lens on your finger and then you put it on your eye. Are we maybe transferring some different types of bacteria onto the surface of the eye?” Park asks. “That’s what we’re conjecturing, but it’s hard to know for sure.”

If so, poor cleaning, or a lack of hand-washing, might offer more opportunities for bacteria to jump from finger to lens to eye. This could possibly be mitigated by using daily lenses rather than monthly or biweekly—that way you’ve at least got a clean one when you start. And while the NYU study didn’t differentiate between the length of lens wear, Park says that clinicians have shifted to recommending daily lenses.

“Simply because you know that you’re taking them out, throwing them away and getting a fresh pair every day when you use them,” she says. “As opposed to that person who’s taking them off, putting them into a solution where there’s a high likelihood that there are bacteria also there and then putting them back in the eyes the next day. So from a clinical standpoint, absolutely we believe that going to the daily wear is probably the safest thing.”

The next steps, Park says, would be to analyze the ocular microbiomes of people who’ve actually gotten some of these infections, and see if they have higher concentrations of some of these bacteria. Another open question is whether, once people have been wearing contacts for many years, their bodies adjust to the new normal. “Does that predispose them or protect them?” Park asks. “That would be an interesting question.”