Your dramatic eye makeup could actually be unhealthy for your eyes assuming you're a contact lens wearer, according to a tiny pilot study that appears in Eye and Contact Lens Science and Clinical Practice. The study involves the "waterline." That's the thin inner portion of the eyelash line, and it's a popular place to apply eyeliner: The waterline has an entire Pinterest board dedicated to it; an Allure article touts the "big, open eyes" you can get from putting makeup on it; and celebs like Selena Gomez apparently favor it. But researchers wanted to quantify how much eyeliner might enter the tear film—which a press release explains is "the thin coating protecting the eye"—when it's applied in one of two places: on the waterline, or outside the lash line, along the skin. The study involved just three female participants who visited twice on separate days.
They were randomly assigned one of the two eyeliner application conditions, and used Avon's "Glimmerstick." Alison Ng, a scientist at Canada's University of Waterloo, took more than 200 frames of video of the subjects' eyes over a two-hour period to record the amount of particles that moved into the tear film. Ng says, "the makeup migration happened quicker and was greater" in the waterline scenarios. "Within five minutes, between 15% and 30% more particles moved into the eye's tear film," the release notes. That could lead to discomfort, says Ng, or cause buildup on the lens (especially when lenses are worn for several days) that could fuel more troublesome problems, like irritation or even an eye infection. "For anyone who wears heavy makeup or enjoys regularly applying beauty products around the eye, I would recommend daily disposable lenses for optimal cleanliness and comfort," she says. (Here's why long lashes are bad for you, too.)