A person's eyes produce mucus or pus known as rheum that leaves behind what are colloquially called eye boogers.
When mucus dries in the eyes, it can leave behind this sludgy substance. Some people refer to it as having "sleep" in the eyes.
Mucus helps protect the eyes from specks of dirt, harmful chemicals, and other foreign materials. Eye boogers are harmless, but changes in discharge from the eyes can give clues to health concerns someone may have.
What are eye boogers?
Woman outside jogging wiping eye boogers away.
Although buildup of mucus in the eyes is often harmless, it may sometimes indicate changes in health.
Eye boogers refer to a buildup of mucus in the eyes.
During the day, each time a person blinks, the eyes flush away the secretions of rheum they have produced. Since the eyes produce this mucus in such small quantities, most people never notice it.
At night, when a person does not blink, the mucus can build up. Sealed eyelids allow it to build up along the eyelashes and in the tear ducts.