Waking up with a crusty substance collected at the corners of the eyes, often called “sleep crust” or “sand in the eyes,” is medically known as rheum or gound. This accumulation is a normal, protective byproduct of the eye’s continuous self-cleaning process. The presence of a small amount of this matter each morning indicates that your eyes effectively cleared away debris and waste while you slept. Understanding the composition of this discharge and the mechanism of its accumulation helps demystify this universal experience.
What Sleep Crust Is Made Of
Sleep crust is a combination of substances found in the tear film that constantly bathes the eye’s surface. The primary ingredient is mucin, a thin, watery mucus produced by the conjunctiva (the clear membrane covering the white of the eye and lining the eyelids). Mucin lubricates the eye and captures foreign particles or waste.
Another component is meibum, an oily substance secreted by the meibomian glands along the eyelid margins. This oil prevents the evaporation of the watery layer of tears and contributes to the discharge’s sticky consistency. These natural secretions mix with shed epithelial cells (dead skin cells from the eye and eyelid surfaces) and environmental debris like dust, creating the final product that crusts overnight.
The Nighttime Mechanism of Accumulation
The material appears upon waking because of the difference between the eye’s daytime and nighttime activity. While awake, blinking acts as a natural windshield wiper. The average person blinks 10 to 20 times per minute, spreading the tear film and washing away accumulating rheum down the nasolacrimal duct (tear duct) in the inner corner of the eye.
Once the eyes close for sleep, this continuous flushing mechanism ceases entirely. The production of the watery component of tears also slows down significantly, allowing mucus, oil, and debris to pool. This mixture collects in the inner and outer corners of the eyelids. As the liquid evaporates over several hours, the remaining solid components dry and harden, forming the characteristic crust, which can be dry and crumbly or sticky and wet.
When to Worry About Eye Discharge
A small amount of dry, white, or pale cream-colored morning rheum is normal. However, a change in the volume, color, or consistency of eye discharge can signal an underlying problem. Normal sleep crust should be easy to remove and not accompanied by other symptoms. If the discharge becomes excessive, persistent throughout the day, or causes discomfort, it warrants attention.
Bacterial Infections
Discharge that is thick, gooey, and distinctly yellow, green, or gray often indicates a bacterial infection, such as bacterial conjunctivitis. This discharge is frequently purulent (containing pus) and can cause the eyelids to stick together tightly upon waking.
Viral Infections and Other Conditions
Viral infections, such as viral conjunctivitis, typically produce a more watery and clear or slightly white discharge, though the volume can be substantial. Other conditions, including blepharitis (inflammation of the eyelids) or severe dry eye, can also lead to abnormal crusting and discharge. Symptoms like eye pain, redness, light sensitivity, blurry vision, or swelling of the eyelids alongside the discharge are warnings that the eye is struggling. If these symptoms are present or if the discharge requires repeated cleaning throughout the day, consult a healthcare professional.