(HealthDay News) — Eye gunk, known medically as rheum, is the crust that forms in the corners of your eyes when you wake up in the morning.

Sleep crust is a mix of mucus, skin cells, oils and tears shed by the eye during sleep, says the University of Utah.

While white or cream colored gunk is normal, yellow or green is not, and can be a sign of conjunctivitis or a chronic eye condition.

The school says you should see an ophthalmologist if your eye gunk is discolored.

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