“Sleep dust,” also known as “eye gunk” or “sleepies,” is a common physiological occurrence that most people experience upon waking. The scientific term for this eye discharge is rheum. This material collects in the inner corners and along the lash line of the eyes while a person is asleep. The presence of a small amount of rheum is a normal sign of healthy eye function and the body’s natural cleansing process.
The Composition of Eye Discharge
The crusty material found in the morning is a concentrated mix of substances that form the eye’s protective tear film and various debris. A major component is mucus, or mucin, which is produced by the conjunctiva, the clear membrane covering the eye and inner eyelid. This mucus helps to lubricate the eye and capture foreign particles, such as dust and airborne allergens.
Another ingredient is meibum, an oily substance secreted by the meibomian glands near the eyelashes. This oil forms the outer layer of the tear film, which prevents the watery tear layer from evaporating too quickly. The accumulation of rheum also includes exfoliated dead skin cells and environmental debris. The final consistency of the rheum, whether wet or dry and crusty, depends on how much liquid content has evaporated overnight.
Why It Accumulates During Sleep
The reason for the morning build-up is the lack of a flushing mechanism while the eyes are closed. During the day, the action of blinking continuously washes away debris and excess tear film components. This motion directs the material toward the tear ducts, which drain into the nasal cavity.
When a person sleeps, the eyelids remain closed, and the blinking action stops. This cessation of flushing allows the debris-laden mucus and oil to gather in the corners of the eye and along the lashes. As the liquid portion of this collected material evaporates over several hours, the remaining solids dry out and form the characteristic crusty residue.
Distinguishing Normal Sleep Dust from Infection
Normal rheum is harmless and appears as a small amount of white, clear, or light cream-colored material that is dry and crusty or slightly sticky. A change in the quantity, color, or texture of eye discharge can signal an underlying health issue. Signs that warrant medical attention include an excessive amount of discharge, especially if it makes the eyelids stick together and is difficult to open in the morning.
Discharge that is thick, gooey, or changes color to green, yellow, or gray may indicate a bacterial infection like conjunctivitis (pink eye). Other concerning symptoms include eye pain, blurred vision, increased sensitivity to light, or redness and swelling around the eye. Conditions such as blepharitis or severe dry eye can also cause an increase in crusting.