Some basic eyeliner safety tips: Don’t put it on in a moving vehicle, don’t use it to write “Kick Me” on someone’s back, don’t swap pencils with your friends in an effort to expand your color palette and/or your microbiome, wash your hands before putting it on, don’t sharpen your pencils with the same knife you just used to dice raw chicken.

And maybe, think twice before using eyeliner too close to your eye. This is the recommendation of a very small pilot study recently published in Eye and Contact Lens Science and Clinical Practice, which found that particles from eyeliner could contaminate the eye—more so the closer it is to the eye’s surface. A logical conclusion, but a notable one for this preliminary attempt to confirm it scientifically.

The waterline—a beauty term, not a medical term—is the line of skin between the eyelashes and the eye. It’s as close to your eye as you can put eyeliner without actually drawing on your cornea. This is what it looks like.

Except, according to this study, it might just amount to drawing on your cornea anyway. Over the course of two visits, researchers drew eyeliner both outside the lash line and “behind the lash line” (or on the waterline) on the three female subjects’ eyes. They used a glittery pencil, because the glitter particles would be easier to track. Then, researchers filmed subjects’ eyes for 30 seconds while they blinked, and analyzed the video to see how many glitter particles ended up in the tear film—the thin coating on the surface of the eye.

It's impossible to make any sweeping statements based on just three subjects, but the study found that there were 15 to 30 percent more particles in the tear film when eyeliner was drawn on the waterline than when it was just outside the lashes. After two hours, though, subjects’ eyes had returned to pre-application glitter levels, so whatever contamination occurs may just be temporary. The eye is pretty good at flushing out unwanted visitors.


Average Number of Particles in Eye Over Time

Eye and Contact Lens Science and Clinical Practice

Small as this study is, the researchers concluded that “it would be beneficial to advise patients to reserve the application of eyeliner pencils to anterior to the lash line.” Especially for people who wear contacts—though the study didn’t look at that, the lead author Alice Ng, of the University of Waterloo in Canada, speculated in a press release: "People who wear contact lenses are most likely to notice some problems. If they have eyeliner stuck to their lenses, increasing deposits might cause vision disruption as the lens becomes cloudier."

Some temporary glitter in your vision may be the worst consequence of coloring too close to your eye—it’s not clear what, if any, effects of long-term exposure there might be. But the Food and Drug Administration also notes that old makeup can get contaminated with bacteria and possibly cause eye infection. For mascara, two to four months is the limit, to be sure you get rid of it before things start growing in those tubes.

In any case, this study is a good reminder that no matter how crisp that line is when you draw it on, the boundary between eye and eyelid is fuzzier. The farther from the eye you draw your eyeliner, the safer you'll be—for maximum safety, consider the bottoms of your feet.