What are eye crusties made of?

What are eye crusties made of
Credit: American Chemical Society.

The substance that builds up in the corners of your eyes as you sleep has a variety of colloquial names:

Eye crusties, sleep, eye dust.

But why does it appear every morning? And what is it actually made of?

In this video, Reactions explains the chemistry of eye crusties:

Reactions is a video series produced by the American Chemical Society and PBS Digital Studios.

The American Chemical Society, the world’s largest scientific society, is a not-for-profit organization chartered by the U.S. Congress.

ACS is a global leader in providing access to chemistry-related information and research through its multiple databases, peer-reviewed journals and scientific conferences. ACS does not conduct research, but publishes and publicizes peer-reviewed scientific studies.

Its main offices are in Washington, D.C., and Columbus, Ohio.

Source: American Chemical Society.