Why Do We Get 'Sleep' In Our Eyes? According to a Huffington Post article:

 "The crusty stuff is actually made up of a bunch of different materials, including discarded cells, mucus and debris (including bacteria, bits of oil from the eyelids, and dust), that are collected as the eyelids sweep across the eye, explains Dr. Ivan Schwab, M.D., a professor of opthalmology at the University of California Davis School of Medicine and a member of the American Academy of Ophthalmology."

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