Crying is one of the most human things we do. We cry when we’re heartbroken, joyous, or overwhelmed. Sometimes, tears come when we don’t expect them — like when a favorite song reminds us of a long-lost friend or a nostalgic movie scene stirs up memories of childhood. Yet, despite how universal it is, the science behind crying remains something of an enigma.

Countless species produce tears to protect and lubricate their eyes, but none cry for feelings of sadness, frustration, or awe. Why do humans shed emotional tears? Over the years, scientists have unraveled parts of this mystery, but much of it remains hidden in the folds of our biology and evolution.

The Types of Tears and Their Origins

Crying has long captivated human curiosity. Ancient texts from the Old Testament describe tears as a physical transformation of a weakened heart into water. The Greeks believed the mind triggered tears, while 17th-century theorists imagined emotions heating the heart to produce vapor that condensed near the eyes.

It wasn’t until 1662 that Danish scientist Niels Stensen traced tears to the lacrimal gland. But even with this anatomical breakthrough, the purpose of tears remained murky. Charles Darwin famously called emotional tears “purposeless,” dismissing them as little more than an odd evolutionary quirk.

Centuries later, scientists are still debating Darwin’s conclusion.

Every tear serves a purpose. Most of the time, our eyes release basal tears, a constant, invisible flow that keeps our eyeballs moist and functional. Then there are reflex tears, the ones that flood our eyes when we chop onions or get poked in the eye. These tears come from glands near our eyebrows and flush out irritants.

But emotional tears are different. Humans alone produce them when they’re moved or distressed. Structurally, these tears aren’t far removed from their reflexive and basal counterparts. They’re mostly water, with oils, mucus, antibacterial proteins, and electrolytes. Yet the trigger comes from somewhere else — parts of the brain associated with our deepest feelings.

When we cry, other parts of the brain activate the cells in the brainstem responsible for tear production. This connection hints at how intertwined our emotional tears are with the human brain. Unlike reflex tears, which follow a clear irritant like dust, emotional tears often emerge from a storm of feelings — grief, joy, or even frustration.

Crying Through the Ages

Crying starts early, but not in the way you might expect. For weeks after birth, infants cry vocally but shed no tears. The iconic image of a newborn bawling with streaming eyes only comes later, when their tear glands mature. Scientists believe this evolution was about survival. A wailing baby ensures its parents’ attention.

Why, then, did humans begin shedding liquid tears during emotional distress, unlike other animals? One theory suggests that scrunching the face to cry may physically stimulate tear glands. Another explanation posits that tears offer a quieter way to communicate. While a baby’s cries can echo through a house, tears let adults signal distress more subtly, without alerting predators.

As we age, the reasons we cry evolve. Physical pain may trigger tears when we’re young, but as we grow, emotional connections take center stage. Sometimes, crying may act like a social glue. Whether it’s homesickness, heartbreak, or grief, these tears tie us to others.

“Tears signal to yourself and other people that there’s some important problem that is at least temporarily beyond your ability to cope,” explains Jonathan Rottenberg, a psychologist at the University of South Florida.

The Social and Personal Side of Tears

The reasons we cry — and how often — vary widely. One of the strongest predictors is gender. Globally, women cry roughly two to three times as often as men. This disparity begins in adolescence, shaped by social expectations and possibly hormones. While testosterone may suppress crying, societal norms also teach boys to “be tough.”

Empathy and personality also play a role. People who are highly empathetic or more neurotic are likelier to cry, as are those who are sleep-deprived or have had a drink.

Despite stereotypes, crying has its benefits. Many people feel a sense of relief after shedding tears, especially when crying leads to support.

Social reactions make a difference, too. Crying can be a signal to others when help is needed. Supportive responses — like a hug or kind words — can amplify the catharsis of tears.

Darwin may have dismissed crying as purposeless, but as researchers dig deeper, they’re discovering just how crucial tears are to the human experience.