The type of crying that we are most familiar with is the shedding of tears as an emotional response. Why we release tears when we feel grief, hurt or joy still confounds the scientific community, but several observations have been made.
Emotionally charged tears contain several protein-based hormones produced at times of stress—specifically prolactin, adrenocorticotropic hormone and leucine encephalin. The altered chemical composition of these tears have led scientists to speculate that crying is the body’s method of ridding excess stress hormones. Otherwise, stress hormones would reach harmful levels within the body. Indeed, this explanation fits well with the anecdotal knowledge that crying allows us to feel better.
More recently, researchers observed that emotional tears could also serve an evolutionary purpose. Excess lacrimal fluid disables the fight-or-flight response when it blurs our vision. By revealing our vulnerability, crying could be seen as a signal for defeat or submission, thereby eliciting mercy or sympathy from an attacker. Similarly, such a show of weakness can evoke pity and help one gain support from a larger community.
So why do we cry? Observationally, we cry because we have something in our eyes, or because we are part of a species that, through evolution, recognizes certain social cues. But more importantly, crying is a form of human expression.