Tears are a weird phenomenon. They serve a fundamental role in the human’s fight against disease. Their emotional function has baffled the greatest minds.  And no other animal sheds tears of sorrow or joy apart from humans. But what is the purpose of this strange fluid? How do some mere drops of water add to the immense immune system and how does it all come together and make the tear that we wipe from our cheeks?
Tears have a multifaceted purpose; they serve both the immune and emotional system. Let’s consider the role of tears in the immune system first. Here, two types of tears are secreted: basal tears and reflex tears. These tears are released by many animals. Basal tears are vital for eye function. They keep it moist, prevent dry spots that interfere with vision and provide cells on the layer of the eye ( the endothelium) with vital nutrients that compensates for the eye’s lack of blood vessels.
Basal tears are secreted all the time.  Whenever we blink ( around once every five seconds ), the fluid is spread across the surface of the eye. Producing it are the lacrimal glands. Our tears also contain natural antibiotics called lysosomes  – they help keep the surface of the eye healthy by fighting off bacteria and viruses. This water is really a saline solution containing minerals and nutrients for a healthy eye. Other glands in the eye are producing oil (called meibomian glands) . Oil is an extremely important component of a tear. The denser oil sits above the saline solution and prevents both evaporation and leakage from the eye. It is these glands that sometimes malfunction and lead to the common disorder ‘dry eyes’. Dry eyes is referred to as Keratoconjunctivitis sicca and is very common. The lack of meibomian gland secretion can mean the tears are not enveloped in a coat, leading to them spilling onto the face. It also leads to a dry cornea between blinks and the eye becomes prone to irritants.
Fighting off such irritants are reflex tears -reflex tears are secreted whenever a foreign stimuli troubles the eye. Whether this is dust particles or irritating vapours, the eye tries to wash it away through these tears. This is why when something is in our eye, we often tear up. We react to bright light through this mechanism too, in order to protect the retina. When the retina is exposed to bright light, the eye constricts the pupil  to decrease the entry of light and produces reflex tears to act as a shade.
The last type of tear is what we are all familiar with: emotional tears.  These tears are produced by the human body when we experience emotional stress. When we laugh intensely, these tears are released. When we are reminded of a depressing memory, these tears are released. When we are in physical pain, these tears are released. A chain reaction occurs in the human body to cause this…
When an emotional situation arises, our limbic system (the part of the brain involved with emotion) sends a message through a neurotransmitter called acetylcholine  to the lacrimal glands to increase tear production.  The chemistry of emotional tears suggests that they contain increased levels of prolactin, adrenocorticotropic hormones and other stress hormones. Their release helps cope with the situation. Though this is just a theory, it is likely that the chemical make-up of an emotional tear vs basal and reflex tears makes it an effective expression of emotion. Some research  is being done that is proposing that the particular reason of a tear’s release plays a part in its chemistry – whether that is joy, excitement, sorrow, pain or irritation.
But emotional tears aren’t simply a biological reaction to some stimuli. They hold a deeper meaning that serves a psychological purpose. If it was simply a way to reduce stress that some memory or circumstance has induced, why is it that babies – who haven’t even developed lacrimal glands and are unable to produce visible tears – are crying all the time? Why does crying just make us feel better? Many psychologists believe that crying elicits help and support from those around us. It makes us vulnerable and makes tearing up a form of desperate communication. Yes, it reduces our heart rate, releases stress hormones and calms us down, but crying is in fact a coping mechanism.
The value of crying may be more about the social response it prompts than its physiological effects.Lauren Bylsma, PhD, University of Pittsburgh.
Crying is a deceptively simple concept- with its many subtleties it is actually an extremely complex mechanism. Tears protect our eyes: the lens through which we experience the world and therefore they are arguably one of the most significant protective systems that guard the body. Crying is also an emotional response but how it plays a part in this is still a mystery. What is clear however is that tears are more than a saline solution that nourishes the eye, they are a signal to everyone around us, they are a means of conveying sentiment. After all, it is humans who cry – and animals who merely produce tears.
- NCBI “The Riddle of Human Emotional Crying: A Challenge for Emotion Researchers” (2019) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6402489/
- Cleveland Clinic “The Tear System” (2020) https://my.clevelandclinic.org/health/diseases/17540-tear-system
- Genome “Lysosomes” (2020) https://www.genome.gov/genetics-glossary/Lysosom
- Wikipedia “Pupillary response” (2020) https://en.wikipedia.org/wiki/Pupillary_response
- AAO “All About Emotional Tears” (2017) https://www.aao.org/eye-health/tips-prevention/all-about-emotional-tears
- Wikipedia “Acetylcholine” (2020) https://en.wikipedia.org/wiki/Acetylcholine
- The Independent “Why do we cry? | The science of tears” (2014) https://www.independent.co.uk/life-style/health-and-families/features/why-do-we-cry-the-science-of-tears-9741287.html
- Smithsonian “The Microscopic Structures of Dried Human Tears” (2013) https://www.smithsonianmag.com/science-nature/the-microscopic-structures-of-dried-human-tears-180947766/