If you wear disposable contacts, you’re probably aware that they’re supposed to be chucked after you use them for a certain number of days. And you also probably also totally ignore that recommendation.

Unfortunately, that’s really not a great idea for a few reasons. 

Over time, your contacts build up proteins on the surface of the lens, which can cause a reaction similar to allergies, says Jeffrey J. Walline, O.D., Ph.D., the associate dean for research at The Ohio State University College of Optometry. Not only can these reactions feel uncomfortable, they can even potentially mess with your vision.

Bacteria is also an issue, and it can build up on your contacts over time, says Laura M. Periman, M.D., an ophthalmologist at Redmond Eye Clinic. And, as you probably can guess, that’s not great for your eyes either. “Bacteria can cause significant, vision-threatening and painful infections of the eye,” she says.

It’s not just bacteria and proteins you have to worry about, either: Wearing contacts past their recommended timeframe can reduce the amount of oxygen that reaches your cornea (i.e. the front of your eye).

That can lead to blood vessels growing in your cornea and increase your risk of an eye infection, Walline says. “Eye infections are very painful and can lead to a permanent loss of vision,” he says. 

Of course, contacts are expensive and, if you’re on a tight budget, it makes sense that you’d try to stretch the time you use them. If you do this and know you’re unlikely to stop, Walline says you’re definitely putting yourself at risk for some eye discomfort and potentially something more serious. “

The far less likely, but far more devastating consequence, is an increased likelihood of an eye infection, which is very painful and can lead to permanent vision loss,” he says. Periman agrees. “Infections are rare, fortunately, with modern contact lenses, but we still see severe cases of infection that can lead to scarring, loss of vision, and rarely, loss of the eye,” she says.

So while devastating consequences may be rare, we are talking about your vision, which is kind of a BFD. If using daily disposables the way they’re designed isn’t in your budget, talk to your doctor about longer-wear contacts—there are lenses out there that are made to be replaced every two weeks, which can help. It’s also important not to shirk on seeing your eye doctor regularly.

“All contact lens wearers should have their eyes examined as recommended by their optometrist,” says Walline. “Prevention of problems is much easier to handle than treatment once the problems blossom.”

And, of course, take care of your contacts—and your eyes. “The better your contact lens wear habits, the more likely you will enjoy more years of comfortable wear,” Periman says.