Have you ever wondered why we cry? If so, you are not alone. People have asked this questions for hundreds of years.
One major breakthrough occurred in the 17th century when a Danish scientist discovered the lacrimal gland. The lacrimal gland is responsible for producing the watery or aqueous component of our tears. The tear film also contains a mucus component produced by goblet cells on the white part of the eye and an oily component produced from the meibomian glands at the edge of our eyelids. These 3 components are joined by enzymes, lipids, metabolites and electrolytes to make up the tear film that coats and lubricates our eyes.
Before we get into why we cry, we will first quickly break down the different types of tears and the 3 main components of the tear film.
3 Main Types of Tears
• Basal Tears – These are the natural tears that continually lubricate the surface of the eye. They provide nourishment and protection to the cornea. A stable tear film is also critical to have crisp, clear, consistent vision.
• Reflex Tears – These are the tears that are produced as a response to a physical trigger. This trigger may be cigarette smoke, the fumes from cutting an onion or getting a foreign body in the eye. They are an important part of our body’s defense against infection.
• Emotional Tears – These tears are produced due to an emotional stimulus such as sadness, joy or fear. It is thought that these tears are unique to humans.
3 Layers to the Tear Film
• Mucus Layer – This is the inside layer that helps the tear film stick to the eye.
• Water Layer – This is the largest component of the tear film and keeps the eye from drying out as well as repels bacteria.
• Oily Layer – This is the outer layer that provides a smooth surface to the tear film while preventing the tear film from evaporating.
Emotional tears were once thought to be without purpose by great minds such as Charles Darwin. However, it is now thought that emotional tears are an important part of social bonding and promote helpful behavior amongst humans.
It is thought that emotional tears developed as a form of vocalization to garner attention or care. Newborns are unable to produce tears, but are able to audibly cry to get needed attention and care. As children develop, they begin to develop tears to accompany this audible cry. These tears are triggered from physical pain and emotions such as sadness.
As we get older, the trigger to produce tears from physical pain lessens. On the contrary, the emotional triggers broaden to include joy, empathy, sympathy and compassion. Thus, as we age the value of crying may evolve from the physical response it generates that increases our chance of survival to a social response that allows us to feel better as a result of emotional or psychological support.
Crying frequency and intensity varies greatly from person to person. It is well accepted that women tend to cry about four times more frequently than men. Their crying also tends to be more intense than that of men.
When we produce emotional tears, the synergistic working of two systems is required. The limbic system, which is a network of structures within the brain that responds to emotional triggers, sends signals to the lacrimal system to produce tears.