First off, it's worth noting that tears, which consist of fatty oils, water, and mucus, have an important function — to keep the surface of our eyes smooth and to protect them from irritants and anything else that might cause an infection, according to the National Eye Institute (NEI).
The lacrimal glands, which are tucked just under your eyebrows, produce water and water-soluble proteins that help nourish your eyes. A mucus-based layer attaches to the water in your eyes to keep them moist, too. This mixture spreads across the eyes when you blink, but it also creates tears whenever you cry or yawn.
As Zeba A. Syed, M.D., a cornea surgeon and assistant professor of ophthalmology at Wills Eye Hospital, explained to Self, "When your eyes tear up, the watery layer is overproduced."
