The Physiology of Crying and Variations in Tear Composition

While I enjoy science, I still really find it uncomfortable to put people in a room and play sad movies for them so they can cry and their tears are researched. Well, it is what it is, as it is just science.

You see, we humans are known to produce tears a lot but unlike animals who produce these tears as a result of irritation to their eyes, such as elephants made to produce tears by irritation from the Lobocraspis Griseifusa moth so as to be able to drink from it, humans produce tears as a by emotion. Even newborns would cry because of so many things after birth.

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Now, there are various theories about why babies cry initially, such as gasping from the first breathtaking air to the lungs being the cause of tears, baby hungry being the cause of first tears, cooler air from the atmosphere hitting their wet skin of the baby being the cause of tear, and so on but I like to think they arrive in this world with a simple message, "Hey, I'm here, and I need your attention!" Of course, that's a bit of humor, but the truth is, babies cry because it's their way of signaling to their caregivers.

But either way, we humans produce tears from emotional events, joy, laughter, sadness, emotional pity, fear, and so on but do you know that the chemical makeup of your tears varies depending on the emotion. We have seen that tears from endogenous depression are different from grief.

Now, let's delve into the fascinating world of tears themselves. Humans have not one but three different types of tears. First, there are basal tears, which consist of three layers: a mucus layer that touches the eyeball, an aqueous layer that acts as a defense against bacteria, and an oily layer that prevents the other layers from evaporating. These tears serve to lubricate, nourish, and protect the cornea, keeping our eyes comfortable.

The second type is reflex tears, a mechanism shared by most animals except amphibians and snakes. These tears are triggered by mechanical, chemical, thermal, or painful stimuli, serving as a defense against irritants like chemicals or foreign bodies.

Lastly, we have psychogenic tears, often referred to as emotional tears. These are unique to humans and are controlled by the prefrontal cortex and the anterior portion of the limbic lobe, regions associated with emotions

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Why do babies cry? Scientists suggest that infant crying is like an "Acoustic Umbilical cord." It prompts parents and caregivers to respond to their needs swiftly. Additionally, some researchers propose that infant crying can increase a mother's breast temperature due to elevated oxytocin secretion, facilitating milk release.

However, as we grow, our forebrains develop, and we transition from crying to speech as a more sophisticated means of communication. It's understandable why individuals might cry when unable to express themselves verbally.

What's intriguing is that the chemical composition of tears from emotional experiences differs significantly from that of irritant-induced tears. Studies have shown that emotional tears contain 24% higher protein concentrations than irritant-induced tears. These tears fall more slowly on the face, contain more stress hormones, and natural painkillers. Tears, in general, consist of water, oils, mucus, antibodies, and unique proteins, making them far more complex than one might imagine.

So, the next time you find yourself shedding tears while chopping onions, remember that those tears have a different chemical makeup compared to the ones born of deep emotions. It's just one more testament to the intricate and wondrous world of science.

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Reference

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https://journals.sagepub.com/doi/10.1177/1049732316673342
https://www.aao.org/eye-health/tips-prevention/facts-about-tears
https://www.medicalreport.kr/news/articleView.html?idxno=39724
https://jps.biomedcentral.com/articles/10.1007/s12576-019-00729-x
https://pubmed.ncbi.nlm.nih.gov/7294117/