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.