When you wake up in the morning, it’s obvious why you have bed head, morning breath, and dried up drool on your cheek, but what causes the crusty, gooey grunge on your eyelashes and in the corners of your eyes? 

Eye specialist Dr. Sherleen Chen says that “sleep sand” is the result of the battle between your tears, and the dust and debris in your eyes. She points out that tears are made up of water, protein, oils and mucous, which typically coat the surface of your eye to keep it moist, and protect it from viruses and bacteria. 

But when you’re asleep and your eyes are closed, you’re not blinking, so, tear production slows to a crawl, and once the dirt and debris in your eyes are no longer being diluted, they clump together. And since your tears tend to collect toward the inside corner of your eye, that’s where the clumps end up. 

And whether your eye crud is wet and sticky, or dry and sandy depends on the quality of your tears. In other words, if your eyes tend to be dry, you end up with more solids than liquid, so, your “sleep sand” will be dry and crumbly.