Emotional, Irritated, Faking It—Why Do Humans Cry?
Humans seem to be the only animals who produce one of three different types of tears. Can you guess what it is? Let’s look at the science behind crying.
You hear some bad news, your friend tells you a really good joke, or you enter a smoky room. All of these events might leave you crying, but all tears are not created equal. The tears our eyes produce actually vary in composition depending on the occasion.
Let’s dig into how our eyes produce tears, the kinds of tears our eyes produce, and why we cry at all.
How are tears made?
Healthy eyes have small organs called lacrimal glands that sit right above the eye and secrete tears when triggered. When tears are produced, blinking then moves them across the surface of the eye before they’re carried away by our tear ducts.
Those tear ducts (also called nasolacrimal ducts) drain into our nose. So when you cry a lot, the tears mix with the mucus in your nose. And if you cry even harder, not all those tears can fit in the drainage system. Instead, they fall out onto your face to make you a snotty, teary mess. Fun!
Since newborn babies don’t yet have fully developed lacrimal glands, they can cry without actually producing any tears.
According to the American Academy of Ophthalmology, we make 15-30 gallons of tears each year. That may sound like a lot, but don’t worry, you won’t run out.
Different kinds of tears
Our eyes make three kinds of tears, each with their own composition or biochemistry.
Basal tears
First up, we make around half a teaspoon each day of something called basal tears. These are the tears responsible for lubricating our eyes so they don’t dry out. Basal tears have three layers:
- An inner mucus layer that keeps them attached to your eye
- An aqueous layer that protects your cornea (and also has some germ-fighting enzymes)
- An oily outer layer that keeps the surface of your eye smooth
Our eyes naturally get drier as we age, and there is a test called the Schirmer test to check that your eyes are producing enough basal tears. In the Schirmer test, if you place a piece of paper at your lower eyelid, 15 millimeters of the paper should be wet after five minutes. Certain activities can increase dry eye, like staring at a computer screen for long periods of time.
Reflex tears
Your eye produces reflex tears in response to an irritant. Ever find yourself crying as you chop an onion? Those are reflex tears. When syn-Propanethial-S-oxide, the gassy chemical irritant produced when you chop onions, hits your eyes, it sends a signal to your lacrimal glands to produce reflex tears to flush out the irritant.
Ever find yourself crying as you chop an onion? Those are reflex tears.
Reflex tears are mostly water since their main job is to wash away invaders, but they’re also suspected to have antibodies that help kill bacteria. Other things that inspire reflex tears can be strong smells, bright lights, dust, chemicals like chlorine, and, again, too much screen time.
Emotional tears
You watched a sad movie on Netflix and now you’re sobbing on the couch. It’s probably no surprise that these tears are called emotional tears.
Emotional tears well up when we experience strong feelings like sadness, fear, or even joy. These are the least-understood type of tears, and they’re still an area of active ophthalmology research. What makes them so mysterious? Well, for starters, they seem to be the only kind of tear that is unique to humans. There is evidence that other animals can feel emotions like empathy, so why are we the only ones that cry?
What makes emotional tears so mysterious? For starters, they seem to be the only kind of tear that is unique to humans.
Emotional tears also appear to be more easily triggered—and by a broader range of emotions—as we get older. Some researchers suspect the evolutionary reason for emotional tears may be the fact that they signal to others that you are sad (or fearful or happy). Sending these signals creates a connection between you and those around you, perhaps by signaling that you are in need. Those connections ultimately increase our chance of survival. There is also a clear advantage to your tears if other people help you solve your problem when they see you crying.
There is also some evidence that emotional tears may help us chemically. Emotional tears have higher levels of adrenocorticotropic hormone, a type of hormone we release in stressful situations, and Leu-enkephalin, an endorphin and natural pain killer.
Do our tears carry away these chemicals in order to release stress and help us stabilize our mood? More research is needed to answer these questions.
Do women cry more than men?
While claims that women are “more emotional” are often dubious, there does seem to be evidence that women cry more frequently than men. In one study of 7,000 people across 37 countries, women self-reported crying emotional tears 30-64 times every year. Men in the study reported crying only 5 to 17 times each year.
Interestingly, these gender differences were more pronounced in countries with cultural norms that allowed for more freedom of expression, described by the study authors as “wealthier, more democratic, and feminine.”
Testosterone, usually found at higher levels in men, might also inhibit crying. One study showed women with higher levels of testosterone, and lower levels of prolactin, a protein known for enabling female mammals to produce milk, cried less than women with the opposite.
What are crocodile tears?
Tears that are insincere or fake are colloquially referred to as crocodile tears. The name comes from a piece of lore that says crocodiles will pretend to cry so their prey will investigate and get into chomp-down range. The phrase “crocodile tears” exists in several languages. It’s an old term that’s based in Latin.
But there is also a real medical condition called crocodile tears syndrome. It afflicts people who cry when they eat or sometimes just think about eating. Some research suggests a person who has broken bones in their face or who is recovering from Bell’s Palsy may be more likely to experience crocodile tears. Nerves in the face that need repair can get reconnected incorrectly so that the tear glands get triggered by the smell of food instead of the salivary glands.
There are physical, emotional, and even evolutionary reasons for crying. So next time you feel the tears welling up, let it out.
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About the Author
Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.
