This is an article from Curious Kids, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky!
Why do tears come out of our eyes when we cry? – Grace, age 9, Melbourne
Hi Grace, thank you for a great question.
We cry, or make tears, for three reasons. First, we need tears to keep our eye healthy, so you can say that our eyes cry a little bit all through the day. These types of tears usually don’t come out of our eyes.
Tears do come out of our eyes when we are emotional – either very sad or happy – or when our eyes are irritated by something, like a bit of dust that gets into our eyes or when we cut an onion.
Tears are needed for our eyes to work properly. Your eye has special parts – called glands – that make tears all day. Normally they only produce a tiny amount of tears – less than half a teaspoon per day. Tears are mostly water and a little bit of salt, but they also have some oil, mucus and chemicals called enzymes that kill germs.
A small amount of oil in tears stops them from evaporating or leaking out of our eyes. If we didn’t have oil in our tears, it would make our eyes really dry and sore.
When you blink, the eyelid spreads the tears around your eye and mucus helps the tears stick to the eyeball. Any tears left over drain through a special drainage system that goes through to your nose.
When we cry – and I hope you don’t cry too often – we make more tears than the eye can hold. This is because the largest tear gland can switch on and produce a lot of tears at once, just like a little fountain.
The part of the brain that switches on the “tear fountain” receives signals from the part of your brain that controls your emotions.
When this happens, the eye can produce more than half a cup of tears in minutes. This is way too much for the eye to hold and our drainage system goes to work. Remember that this drainage system goes to our noses? That’s why when you cry you may notice your nose starts running. These are these extra tears.
If you cry really hard, then there are far too many tears even for that drainage system to remove, so the tears start falling out of our eyes.Teresa Trimm/flickr, CC BY-SA
Psychologists believe that crying because of emotions is something only humans do. Most of us cry sometimes because we are really sad. Some of us also cry when we are happy.
We haven’t figured out exactly why we cry when we are emotional, but we do know that the chemicals found in emotional tears are different to normal tears. Some scientists believe that these chemicals may help us feel better after we cry.
There are also some strange conditions that can make people cry. Some people cry when they eat or even just think about food. This is called “crocodile tears syndrome”. It is named after a legend that said crocodiles pretend to cry to trick their prey into coming closer to them.
Crocodile tears syndrome may happen after someone has been in an accident and broken some bones in their face. As the face heals, some body parts called nerves repair themselves in the wrong way. Nerves that made your mouth water when you smell good food get mistakenly connected to the tear gland instead. Afterwards when that person eats or smells something delicious that makes their mouth water, they start to cry.
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Michelle Moscova does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
Authors: Michelle Moscova, Senior Lecturer in Anatomy, UNSW