What are human tears made of?

According to St Luke's Cataract and Laser Institute, human tears consist of three different layers: mucous, water and oil. Every time the eye blinks the eyelids spread a tear film over the surface of the eyeball.

The meibomian glands produce the oily layer, which lines the edges of each eyelid. The lacrimal glands produce the watery part of the tear film. The lacrimal gland is located under the orbital rim below the area of the eyebrow. The microscopic goblet cells situated in the conjunctiva produce the mucous for the eyes. Blinking motions caused by the eyelids carry tears into drains at each corner of the lower and upper eyelids.