Facing forward into a gust of wind or looking down at the onion on your cutting board, tears might spring to your eyes. Trying to stifle a yawn or control a big bout of laughter, tears may build up and run down your cheek.
These are called reflex tears. As the name implies, reflex tears can spout up in an instant. They are made up of the lubricating film that covers your eyes. This film has three layers, including a lipid layer from oil glands, a water solution from the lacrimal glands around the eyes, and a secretion of mucous. This coating keeps your eyes moist, and then drains through the tiny pores at the corner of your eyes.
This film can well up whenever we come into contact with irritants—like when acid from fresh cut chilies or some other aggravating substance lands on your cornea or gets into your mouth.
Reflex tears can also come from muscle tension on our tear glands. This can happen during coughing or vomiting or yawning. All these reactions cause your facial muscles to contract. That increases the emission of tears, but also dams up the tiny pores at the corners of our eyes and prevents the tears from draining.
Tearing up while laughing is a special case. This might come from too much muscle pressure as well. Though, it’s likely that crying while laughing is partially a psychological reaction to an increase in emotion.Whatever the cause, reflex tears contain antibodies and enzymes that protect you against infection and keep your eyes healthy.