Tracing eyeliner onto your inner eyelids can give your eyes a bold, defined look.
Unfortunately, it's also the most unhealthy and uncomfortable way to use eyeliner -- especially if you wear contact lenses or suffer from sensitive or dry eyes.
A small pilot study published recently in the journal Eye and Contact Lens Science and Clinical Practice found that when eyeliner is applied to the inner lids, glitter and pigmentation make their way onto the "tear film" (the eyeball's protective coating) 15 to 30 percent more often than eyeliner applied outside the lash lines. Eyeliner applied on the inner lid also migrated onto the tear film faster than the eyeliner applied above or below eyelashes, and with either application, the glitter didn't stop migrating until two hours after application.
To document the eyeliner migration, Dr. Alison Ng of the Centre for Contact Lens Research at University of Waterloo (formerly of Cardiff University in Wales) used video to count and then compare the many different glitter particles that migrated onto the eyes after different eyeliner placements.
Eyeliner compounds like wax or oil can irritate sensitive eyes or stain and smudge contact lenses, leading to increasingly obscured vision throughout the day, Ng explained in a statement about her study. However, Ng's research didn't examine the potential for eyeliners to bacterially infect users if cosmetics are old or shared, although other studies have in the past. She also notes in her study that the participants were all caucasian, which may mean that eyeliner could have different migration patterns in other ethnicities who have different eyelid shapes.