<P> Rheum ( / ˈruːm / ; from Greek : ῥεῦμα rheuma `` 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 - seeds , sleepy buds , sleepy sand , eye goop , cheese , or sleepy dust . </P>
where does the crust in your eyes come from
mucin discharged from the cornea or the conjunctiva