All mammals produce tears round the clock to make sure their eyes don’t dry out and in response to irritation, but “psychic” tears—the type produced as part of an emotional response that lead to crying—are exclusive to humans. They even have a different chemical makeup, which includes leucine-enkephalin, an endorphin and natural pain killer. Hence, that feeling of having had “a good cry.”
Crying begins in the limbic system, which is the part of our brains that manages emotion through the autonomic nervous system and controls involuntary responses. That system is divided into two parts: sympathetic, which produces aggressive responses; and parasympathetic, which helps us process our emotions and ultimately rest. “Crying will often begin as part of a sympathetic response—‘I can’t have that cookie’ or ‘I want more screen time’—but the full-on waterworks only arrive as part of a parasympathetic response,” says Deborah MacNamara, a developmental science expert and clinical counsellor. “So by the time a child is sad-sobbing, their brain has shifted from pursuit to sadness, and it has already processed the futility of the outcome they were hoping for.” Then the brain moves toward acceptance and adaptation, she explains.
The actual waterworks are the product of our lacrimal gland, which sits beside each eye and is both secretory (meaning it creates tears), and excretory (meaning it gets rid of them). Or at least that’s what it does when you’re not having a heightened emotional experience. When we cry, our eyes are like the doorman at an extremely packed nightclub who gets trampled while trying to let people out one by one. Some impatient clubbers even take the back exit (a.k.a. your nasal cavity), as tears mix with mucus and produce a runny nose.
For parents whose hearts break a little every time the sad tears start flowing, it can be helpful to understand that the tears are a signal the process of healing is underway. MacNamara says those those early, sputtering tears are a response to anger and frustration—she likens them to an engine revving and getting caught before it can slide into gear. Whereas what Oprah might call the “full-on ugly cry” means the transition has occurred. This sort of sob fest even has an evolutionary purpose, as it signals to the people nearby that a child is in need of comfort.