Why do we sometimes cry when we laugh?

Weeping with laughter, sobbing in sorrow: Our bodies react similarly when emotions run high. A few scientists have explored the phys­ical pathways of emotional tears, but none have categorically stated why these tears exist. Tom Lutz, author of Crying: The Natural and Cultural History of Tears, notes Darwin published snapshots of laughing and crying people to demonstrate that the same expression accompanies both behaviours. ''Some tears are squeezed out of the ducts simply because the face is scrunched up,'' explains Lutz. ''But tears also accompany the body's return to homeostasis after extreme excitation. So after a big laughing jag, tears are a sign that the body is returning to normal.''

What tears are made of, however, may offer further clues about why we cry. Unlike tears that well up when you chop onions, emotional tears are unusually rich in protein-based hormones that spike when you're stressed. This fact led one US biochemist to theorise that releasing tears – and thus the hormones in them – may be the body's attempt to reduce stress. Regardless of its cause – be it pleas­ure or pain – people do tend to feel better after a good cry.

~Reader's Digest