Tears are produced by the lacrimal glands to keep the eye moist and to wash away dust, dirt, germs, and other irritating substances. Tears are formed to keep the eye moist under normal conditions and also in response to an irritant (such as an eyelash in the eye) or emotion.

For a person to see well, he or she must produce enough tears to keep the eye moist, and have a drainage system for tears that functions properly. When tears cannot drain from the eye, they frequently build up around the eyeball and flow down the cheek or nose.