The crusty material that collects at the corners of your eyes while you sleep, often called “sleep sand” or “eye gunk,” has a medical name: rheum or gound. This accumulation is a common biological phenomenon that occurs when the eye’s natural protective mechanisms operate without the benefit of blinking. The eye continuously produces a mix of substances to keep its surface clean and lubricated, and this material simply dries out overnight. Understanding how this material forms and what it contains can help you distinguish between a harmless morning annoyance and a potential sign of an underlying eye condition.
The Natural Process of Rheum Formation
The human eye relies on the act of blinking throughout the day to distribute the tear film and wash away debris. Each blink sweeps away microscopic particles, old cells, and excess fluids through the nasolacrimal duct, or tear duct, which drains into the nose. When you are asleep, this cleansing action stops entirely, allowing the material being produced to collect along the eyelash line and in the inner corner of the eye.
The process of accumulation is aided by the change in the eye’s environment during sleep. Since the eyelids are closed, the tear film is not exposed to air, but the fluid components of the collected material still partially evaporate. This evaporation concentrates the remaining solids, causing the discharge to transition from a moist substance to the drier, crusty texture found upon waking. The material then consolidates into flakes or sticky strings at the junction of the upper and lower eyelids.
The Makeup of “Sleep Sand”
The crusty residue is primarily composed of mucus, oil, and epithelial cells. The mucus, or mucin, is produced by the conjunctiva, the clear membrane covering the white part of the eye and the inner surface of the eyelids. This mucin forms the sticky, stringy base of the rheum.
The oily component comes from the meibomian glands located within the eyelids, which secrete a lipid substance called meibum. Meibum is designed to coat the tear film and prevent its rapid evaporation, but a surplus can mix with the mucus and solidify. These biological secretions combine with dead skin cells exfoliated from the eyelid margins and environmental debris like dust. The final texture, whether dry and sandy or wet and sticky, depends on the ratio of water that has evaporated from the mixture overnight.
Identifying Abnormal Discharge and When to Consult a Doctor
While some amount of pale, whitish, or light cream-colored rheum is normal, a change in the quantity, color, or consistency can signal an underlying health issue. When the discharge becomes excessive, causing the eyelids to stick together and making it difficult to open the eyes, it warrants closer attention. This increased stickiness can indicate an infection or inflammation.
A significant warning sign is a change in the color of the discharge to yellow, dark yellow, or green, as this often suggests a bacterial infection, such as bacterial conjunctivitis, commonly known as pink eye. Other symptoms that accompany abnormal discharge are equally important, including pain in the eye, significant redness or swelling around the eye, and increased sensitivity to light (photophobia).
Conditions like severe dry eye, which causes the eye to overproduce compensatory mucus, or blepharitis, an inflammation of the eyelid margins, can also lead to an increase in crusty discharge. If you experience any of these specific changes or symptoms, consulting an eye care professional is recommended for an accurate diagnosis and appropriate guidance.