The medical name for “morning sleep” or eye crust is rheum, he says Ashley Hayden, MDa board-certified eye surgeon and co-founder of GentleDrop. “It’s made up of normal biological material found around the eye, including mucus, dry tears and shed skin cells,” she adds. The reason we don’t accumulate it while we’re awake is because we shut it down intermittently, but at night, that cleaning system isn’t active.

Eye crust can look a little different for everyone, he adds Sonia Kelley, OD, MSan optometrist and eye health expert with EyeBuyDirect — can be yellow, crusty, clear, sticky, or thin and watery.

Excess eye crust can form for a number of reasons and can sometimes signal an eye health problem.

Dry weather

If you live in a dry climate or when cold weather makes your skin feel especially dry, that could be responsible for the mucus build-up, says Dr. Hayden. Chronic dry eyea condition where the eye doesn’t lubricate itself naturally, can also be exacerbated by these conditions, Dr. Kelley adds. “This can lead to a sticky, stringy mucus residue and discharge on the surface of the eyes,” she says.

Blepharitis

“Blepharitis is when the eyelids become inflamed and you see a frothy yellowish-white discharge. It’s often due to blocked oil glands, skin conditions, or mites,” says Dr. Kelley.

Meibomian gland disease (MGD)

MGD is a condition caused by blockage of oil glands (also called Meibomian glands), or glands that irregularly produce the lubrication the eye needs, Dr. Hayden explains. “This is due to low-grade inflammation of the oil gland, which results in thick, dirty secretions instead of the more normal viscous oil,” she adds.

Allergic reactions or infection

Infections like pink eye or allergic reactions can also trigger excessive eye debris. “In this case, one would notice excessive or abnormal discharge—changes in amount, color, or consistency,” says Dr. Kelley.

Treatment for crusted eyes depends on its cause, but some general tips from experts are:

Try warm compresses: “For mild blepharitis and MGD, there are a variety of effective home remedies,” says Dr. Hayden. “We recommend starting with warm compresses in the morning and before bed to help loosen up the Meibomian glands.”

Keep the eye area clean: An over-the-counter eyelid scrub or gentle cleansing of the lash line with baby shampoo helps, adds Dr. Hayden. It’s also essential to remove eye makeup at night and regularly replace products like mascara and eyeliner, which can harbor bacteria.

Do not sleep under a fan: If you put the fans to sleep, try to point it away from your face. “Air movement can cause tears to evaporate quickly overnight, leading to symptoms the next day,” it says Jovi Boparai, MDan ophthalmic surgeon and co-founder of CorneaCare. To supplement the drying of the room, he recommends sleeping with a cool mist humidifier in the room.

Remove the contact lenses: If your lenses aren’t meant to be worn in, be diligent about removing them and wash your hands before doing so, says Dr. Kelley.

While we all deal with crusty eyes, it can be a sign of something serious. “If your eyes are closed in the morning and you can’t open them, please call an eye care provider,” says Dr. Hayden, because it could be a sign of infection.

It’s normal to see some stuffiness when you have a cold or sinus problems, however, “you shouldn’t have red or irritated eyes,” adds Dr. Hayden. “Crustaceans should also not affect your vision. If you experience a change in vision or eye pain, please call your local ophthalmologist or optometrist.”