system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: what is the crust in your eyes when you wake up? Do some people get more or less? Why?
gpt
It's mostly salt and other parts of the tear liquid. Your body constantly covers your eyes with tears to keep them moist. Normally we blink to disperse that liquid. When you sleep you might produce more tears than you need to keep the eyes moist and some leaks out from underneath your eyelids. What is called sleep is what remains on your skin after the leaked tears dry out.