The substance commonly known as “sleep sand,” “eye crust,” or “sleepies” has a formal name: rheum. This natural discharge gathers at the inner corners of the eyes or along the lash line, typically noticed upon waking. Rheum is a normal physiological byproduct of the eye’s constant, protective self-cleaning mechanism. The production of this material is a healthy sign that the ocular surface is successfully clearing away foreign particles and cellular debris. The amount of rheum produced can vary slightly from person to person and night to night.
The Components of Rheum
Rheum is a complex mixture. A primary component is mucus, or mucin, secreted by the conjunctiva, the clear membrane covering the white of the eye and lining the eyelid. This water-soluble material serves a protective function by trapping small contaminants, such as dust, pollen, and environmental irritants. The discharge also contains meibum, a natural, fatty oil produced by the meibomian glands within the eyelids. This oily substance is essential for maintaining the tear film’s stability and preventing its rapid evaporation. Rheum further incorporates exfoliated skin cells from the eyelid and lash line, along with airborne debris collected by the tear film.
Why Does Rheum Accumulate During Sleep?
During waking hours, the eye continuously produces rheum components, but blinking prevents accumulation. The average person blinks between 15 and 20 times per minute, and each blink acts like a windshield wiper, spreading the tear film smoothly across the eye’s surface. This constant movement flushes the debris-laden tear fluid towards the nasolacrimal ducts, which lead to the tear drainage system inside the nasal cavity. The lacrimal system actively drains this fluid, preventing buildup during the day.
When a person falls asleep, this natural flushing mechanism abruptly stops. Since blinking ceases, the protective components secreted by the eye remain on the ocular surface. The watery part of the tear film then evaporates, leaving the mucus, oils, and cellular matter behind, especially at the inner corner near the drainage point. These remaining, concentrated substances pool, dry, and solidify into the characteristic crusty or sticky rheum.
Identifying Concerning Eye Discharge
While a small amount of clear or light-colored rheum is normal, certain changes signal an underlying medical problem. Discharge that is thick, sticky, or excessive often indicates an issue beyond typical overnight accumulation. A significant change in color to yellow, green, or gray suggests a bacterial infection, such as bacterial conjunctivitis (pink eye). This discharge may become pus-like (purulent), sometimes substantial enough to seal the eyelids shut upon waking. Viral infections often produce a thinner, more watery discharge that may contain a whitish or light yellow component. Any accompanying symptom, such as persistent eye redness, pain, increased light sensitivity, or blurred vision, warrants consulting a healthcare professional.
Proper Hygiene for Eye Crusts
When removing normal rheum, thoroughly wash your hands first to prevent introducing germs to the eye. Resist the urge to rub the crust away with bare fingers, which can irritate the delicate eyelid skin. Instead, soak a clean washcloth in warm water and gently apply it as a compress over the closed eye for a few moments. The warmth helps to soften and loosen the dried material before wiping it away. Wipe gently in a direction moving away from the eye itself, using a separate, clean section of the cloth for each eye to avoid cross-contamination.