Tears of joy, tears of sadness, tears of frustration or tears of pain - humans are thought to be the only animals that cry tears of emotion. CrowdScience listener Lizzy wants to know: why do we cry for emotional reasons? What is its evolutionary benefit? And why do some people cry more than others?

It turns out that humans cry three types of tear: basal, reflex and emotional. The first kind keeps our eyes nice and lubricated and the second flushes out irritants such as fumes from the pesky onion, but the reasons for emotional tears are a bit harder to pin down.

Using a specially designed tear collection kit, presenter Caroline Steel collects all three kinds of tears. With them safely stashed in tiny vials, she heads to the Netherlands, to Maurice Mikkers’ Imaginarium of Tears. Looking at her crystallised tears under a microscope will hopefully unveil a mystery or two.

Marie Bannier-Hélaouët, who grew tear glands for her PhD, explains how the nervous system processes our emotions into tears. But why should we cry for both happiness and sadness, and for so many other emotions in between? Ad Vingerhoets, Professor of Clinical Psychology at Tilburg University, suggests we cry for helplessness - our bodies do not know how to process such intensity of feeling.

But do these tears bring relief? Lauren Bylsma, Associate Professor of Psychiatry at the University of Pittsburgh, has been studying heart rates during crying episodes to find out. With her help, we also explore if women do in fact cry more than men, and why that might be.

Presenter: Caroline Steel

Producer: Eloise Stevens

Editor: Ben Motley

Photo: Fisheye woman having a cry - stock photo Credit: sdominick via Getty Images)