Rheum is a thin mucus that is naturally discharged from the eyes, nose, or mouth, often during sleep. It is a combination of mucus, tears, and skin cells. Healthy rheum is clear or light yellow and may be hard, sludgy, or thin after sleeping, but should not be noticeable during the day. However, if the mucus is very thick, green, dark yellow, or occurs with pain or redness in the eyes, it could be a sign of an eye infection.

Rheum from the eyes is particularly common, and dried rheum near the eyes is commonly called sleep, sleepy-seeds, sleepy buds, sleepy bugs, sleepy sand, sleepy winks, eye boogers, Sandmans sand, eye goop, sleepy dust, sleepies, eye gunk, eye crust, sleepy men, crusties, dozy dust, eye globs, or sleepy dirt. When an individual is awake, blinking of the eyelid causes rheum to be washed away with tears via the nasolacrimal duct. However, the absence of this action during sleep results in a small amount of dry rheum accumulating in the corners of the eye.

If an individual has more rheum than most, they may be suffering from one of a few different conditions. Conjunctivitis (pink eye), chlamydia, infection of the eyelid (blepharitis), and more can all cause an excess of rheum, especially in the eyes. In the case of allergic conjunctivitis, the buildup of rheum can be considerable, preventing the patient from opening one or both of the eyes upon waking without prior cleansing of the eye area.

Although its tempting to rub your eyes with your hands in the morning, its never a good idea, as germs on your hands could lead to an eye infection. The best way to remove rheum is to use a warm, damp washcloth to gently wipe the eyes.