<P> Rheum (/ ˈruːm /; from Greek: ῥεῦμα rheume "a flowing, rheum"), also known as gound, is thin mucus naturally discharged from the eyes, nose, or mouth during sleep (cf . mucopurulent discharge). Rheum dries and gathers as a crust in the corners of the eyes or the mouth, on the eyelids, or under the nose . It is formed by a combination of mucus (in the case of the eyes, consisting of mucin discharged from the cornea or the conjunctiva), nasal mucus, blood cells, skin cells, or dust . Rheum from the eyes is particularly common . Dried rheum is commonly called sleep, sleepy sand, eye goop or sleep dust . </P> <P> When the individual is awake, blinking of the eyelid causes rheum to be washed away with tears via the nasolacrimal duct . The absence of this action during sleep, however, results in a small amount of dry rheum accumulating in corners of the eye, most notably in children . </P> <P> A number of conditions can increase the production of rheum in the eye . In the case of allergic conjunctivitis, the buildup of rheum can be considerable, many times preventing the sufferer from opening the eye upon waking without prior cleansing of the eye area . The presence of pus in an instance of heavy rheum buildup can indicate dry eye or conjunctivitis, among other infections . </P>

Why do we get stuff in our eyes when we sleep