Science Questions

Why do we cry?

Sat, 8th May 2010

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Joe DeLuco, Anthony Byrne, John France, Andy Leonard and Emz Bamber. asked:

Why do we cry? What it it's purpose and how has it evolved in humans? Why do some people laugh and cry at the same time? Is it also possible to biochemically distinguish crocodile tears from real tears?


Its obviously a very highly evolved behaviour because we are the only animals that do it.  Other animals, although this is possibly disputed by some scientists, don't appear to cry.  Its thought that you cry in response to a stimulus, some scientists thought it might be to do with the build up of stress and hormones - a hormone called adrenocorticotropic hormone might actually be released through the tears.  So when you're in a stressful or unhappy situation, you actually release this hormone and get it out of your body through your tears.  There is evidence for certain hormones found in your tears, things like the hormone prolactin, other things like potassium and manganese.  And so, tears produced when you're crying for emotional reasons actually have more of these things in than tears that are just lubricating your eyelids.  So perhaps, you might be able to tell if someone is just faking it or just the got onions out by measuring these hormones in their tears. 

Interestingly, another thing about crying, women do cry more than men.  Its thought to be to do with certain hormones that are only found in women.  As studies showed on average that men cry about once a month, women cry about five times a month on average.  (More around the time of the month ladies.)

The other interesting thing about crying is that it may well have evolved as a communication signal to say, I'm really unhappy and I need a cuddle or I'm really upset.  I'm really angry.  I'm really stressed.  Because obviously, people can see your tears and respond to them, so it may well be some kind of signal - showing that you're vulnerable, that you're unhappy - that other people can respond to.


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Joe DeLuco asked the Naked Scientists: My question is about crying, specifically tears...why do we shed tears be if for pain, joy or even a mushy movie? What do you think? joedeluco, Sat, 8th May 2010

I'm not really sure why that happens. I don't really cry very often any more but I did when I was younger. I have been seriously choked up before because of a movie but I'm not sure what causes that reaction. I think its built into our psychology. Actually, it might be healthy to clear out the tear ducts every once in a while. aaron28, Sat, 8th May 2010

Studies show that the chemical make-up of tears is different depending on the emotional response. I suspect that why we shed tears differs for this reason.

JnA, Sun, 9th May 2010

SWAG Biwy, Wed, 27th Feb 2013

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