What Is The Crusty “Sleep” In Our Eyes When We Wake Up?

The alarm blares in your ear, jolting you from some wonderful dream where you weren’t working in a dead-end job, had a stunningly beautiful wife, and a shiny convertible in your driveway. Unfortunately, as the alarm clock reminds you, it had all been a dream, and now you’re awake.

However, something else happened while you were sleeping, even though you were knocked out for hours. Your vision isn’t quite clear as you squint at the clock, so you instinctively rub at the corners of your eyes. When you pull your fingers away, you probably aren’t surprised to find small, gooey, crusty, yellow or green “sleep crumbs”.

There are certain things our body does that we eventually get used to, but this bizarre phenomena of our eyes deserves a bit more attention!

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What the Heck Are Those Crusty Crumbs?

Depending on how old you are, or what part of the world you live in, you may refer to those crumbs as “eye boogers”, “sleep”, “eye crusties”, “sleepies”, or “rheum”, which is the formal scientific name for any type of discharge from the eyes, nose, mouth, or ears. While leaking mucus from these orifices doesn’t sound particularly health, it’s actually completely natural, and rather harmless.

More specifically, rheum from the eye is called “gound”, and the trend of strangely named words continues! Gound is a combination of dust, skin cells, and blood cells that blend with mucus and and a material called meibum. The mucus comes from the cornea or conjuctiva, while the meibum is released from meibomian glands.

Credit: Alila Medical Media/Shutterstock

Credit: Alila Medical Media/Shutterstock

Essentially, when we sleep, our eyes behave much differently than they do during the day. We always have rheum in our eyes, but our continuous blinking while we’re awake clears away this mucus and eliminates it from our eyes via the nasolacrimal duct. However, when we’re sleeping, the rheum begins to accumulate along the edges of the eyelids, and the corners of the eye.

Our eyes have three layers, the glycocalyx layer (composed of mucus), which covers the cornea and provides a base for the second layer, which is our tear solution layer. That second layer is crucial to our vision and eye health, as it keeps the eyes lubricated and eliminates foreign objects in the eye. The final layer is made of meibum, primarily composed of fatty acids and cholesterol.

Essentially, rheum is a mixture of these layers (including normal tears) that blends when the muscles of the eye relax. The green, yellow, or whitish color of the “sleep” in your eye comes primarily from meibum, which is a clear fluid when a human’s body temperature is normal.

At night, when our muscles are relaxed, the meibum gland is less able to contain itself, so more of this material is released. Furthermore, as our blood flow diminishes and body temperature drops, that excess meibum can fall below its melting point (only a degree or two) and become a solid! Then… voila! Eye boogers!

Does it Serve Any Real Purpose?

In the morning, it seems to do little more than annoy us, but is there any value to the sleep that we wake up with every morning? Does that rheum and gound serve a real purpose for us?

Ensuring that your eye remains moist is one of the most important functions of the tear ducts and the various layers covering your eye. At a very basic level, meibum prevents us from crying constantly, as it effectively prevents the tears from running down our cheeks by holding them in place. Not only does this keep us from looking like we’re constantly upset, but it also maintains a hydrated surface of the eye.


Every time we blink, a bit more meibum is spread across the eye surface (where meibum is already being secreted). There, it mixes with liquid tears to form the “tear film”. This protects the eye in a coating of liquid, but is very fragile. This coating can quickly break down if you consciously prevent yourself from blinking. When this tear film dissolves, it exposes the cornea to air, as well as any other particles that could scratch or tear that delicate tissue.

Meibum, the primary ingredient in “eye boogers”, is a crucial part of our eye health, and something that is far too often overlooked. We may think of the little crusties as annoying, or maybe even disgusting (particularly when they’re still a bit gooey), but we wouldn’t be able to see or experience the world nearly as well without it.


Next time your eyes are dry, try blinking a few times to get that meibum mixture back in action, and never take the “sleep” in your eyes for granted again!

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About the Author

John Staughton is a traveling writer, editor, publisher and photographer who earned his English and Integrative Biology degrees from the University of Illinois. He is the co-founder of a literary journal, Sheriff Nottingham, and the Content Director for Stain’d Arts, an arts nonprofit based in Denver. On a perpetual journey towards the idea of home, he uses words to educate, inspire, uplift and evolve.

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